LECTURE NOTES
ON
NATURAL RESOURCE MANAGEMENT
Compiled by
Dr.P.Thyagarajan, Ph.D.,
Professor of Soil Science (Retd.)
Tamilnadu Agricultural University, Coimbatore.
&
Guest Faculty
State Forest Service College, R.S. Puram, Coimbatore.
STATE FOREST SERVICE COLLEGE
COIMBATORE
2008
1
JOSE T.MATHEW I.F.S
PRINCIPAL
STATE FOREST SERVICE COLLEGE
Coimbatore
Date :.............
FORWARD
The natural resources viz. land, water and vegetation are the utmost
needs for a better livelihood. Livelihood is a combination of resources used
and the activities undertaken in order to live comfortably. The precious and
vital resources are currently facing multiple crisis driven by ruinous
successive droughts, crashing commodity prices and deteriorating farm
incomes, natural calamities like earthquake, tsunamis and anthropogenic
climatic change. Natural Resource Management seeks to increase agriculture,
forestry and wild life productivity through adoption of practices that sustain
the long term ecological and biological productivity. Inefficient and over
utilization of these natural resources lead to their degradation and exhaustion
resulting in poverty and food insecurity. Poverty is a threat to prosperity
anywhere and everywhere.
Agricultural sector and forestry sector in India are undergoing a
continuous transformation since independence. But the objectives of these
sectors, which are primarily concerned with conservation of land resources,
remains stable and constant, but the strategies adopted to achieve this, is
undergoing continuous changes. Traditional soil management practices
should be replaced with modern and scientific soil health management
technologies. Conservation and management of natural resources involves
rational utilization of land and water resource for optimum production of
vegetation without causing any hazard or deterioration of natural resources,
thereby enhancing the life span of the resources. For this rational land
allocation to forests and wildlife is important.
Considering these aspects, the Forest Officers of this State Forest
Service College are given theoretical and practical training / lectures so as to
enable them to adopt better natural resource management strategies. The
lectures offered by Dr. P. Thyagarajan, professor of Soil Science (Retd.) from
Tamil Nadu Agricultural University, Coimbatore and Guest Lecturer of State
Forest Service College, Coimbatore for the forest officers have been compiled
by him into a booklet form. This booklet is found to be noteworthy,
praiseworthy and extremely useful for their project implementation in the
forest and thereby to manage the natural resources.
I congratulate the course teacher. Dr. P. Thyagarajan for his best and
unstinting efforts in bringing out this booklet containing the course reading
materials.
PRINCIPAL
STATE FOREST SERVICE COLLEGE
Coimbatore
2
CONTENTS
Page No.
PART A- GEOLOGY & SOIL SCIENCE
SECTION A - GEOLOGY
4
SECTION B – SOIL SCIENCE
41
PART B- LAND USES & WATERSHED MANAGEMENT
SECTION C - HYDROLOGY
91
SECTION D - WATERSHED MANAGEMENT
121
SECTION E - WASTE LAND MANAGEMENT
155
3
PART A- GEOLOGY & SOIL SCIENCE
SECTION A - GEOLOGY
Type of rocks:
Geology deals with the study of the earth, composed of minerals,
rocks, fossils etc., and the various processes acting upon it. It has been
divided in a number of branches.
1. Physical geology or Dynamic geology
Deals with the physical features of the earth surface. Also deals with
the geological agents viz., earthquake, volcanoes, springs, winds, frost,
glaciers, rivers, underground water, mountain etc act upon the earth surface.
2. Structural geology
Deals with the structures that have been formed on and inside the
earth. Study of the architecture of the earth surface.
3. Mineralogy
Deals with the study of minerals, which are solid part of the universe.
Aggregates of minerals are rocks.
4.Petrology
Deals with the study of rocks.
5. Stratigraphy
Deals with the succession of rocks formations. Study of geological
history of the earth from a study of rock beds which lie here and there on the
surface of the globe.
6. Palaeontology
Study of fossils of ancient animals, plants and microorganism
(fossilalogy). A remnant or impressions of animals or plant preserved in earth.
Fossilize turn into fossils or petrify. Fossils help in understanding the evolution
of the earth.
7. Economic geology
Deals with the economically viable minerals.
Introduction
The earth and the heavenly bodies in the sky make the universe. The
universe is a vast space in which the sun, the nine planets moon (Satellite),
meteoroids, stars, galaxies, nebulae, asteroids and every thing else exist. The
4
universe or the cosmos includes every thing from the smallest subatomic
particle to the mightiest system of stars i.e., the earth and the heavenly bodies
in the sky make the universe.
The exact age of the universe as estimated recently by NASA is 13.7
billion years after the theoretical big bang theory or evolutionary theory. Other
theories regarding the origin of the universe are ‘Steady State Theory’ and
‘Pulsating theory’.
Like wise there are many theories for the origin of the earth.
1. Evolutionary or natural theory.
a. The gaseous or nebular hypothesis of Kant.
b. The nebular hypothesis of Lap lace
2. Cataclysmic or catastrophic theory
a. Planetismal hypothesis of Chamberlin and Moultan
b. The tidal theory of Jeans and Jeffreys
c. The binary star hypothesis of Russell
d. The supernova hypothesis of Hoyle and lyttleton
e. The inter- stellar dust hypothesis of otto schimdt.
The age of the earth is 4600 million years old. There is a theory that
the gaseous mass that separated from the sun condensed due to continuous
cooling and became the spherical earth overtime. The organization of the
molten earth into various layers having different densities is called
differentiation.
The chronology of the earth history has been divided in to two major
divisions in the geologic time scale. They are highly unequal in their duration.
a. Cryptozoic eon or Precambrian eon.
•
Is 3900 mi yrs duration, during the period, the earth had completed the
process of gathering together most of its rocky substances i.e., around the
world, a great tracts of igneous, metamorphic, and sedimentary rocks
occurred. i.e, inorganic evolution.
b. Phanerozoic eon
•
Is 600 mi yrs duration i.e., period with identifiable life forms developed and
proliferated during the eon- organic evolution.
The organisation of molten earth in-to various layers having different
densities is called differentiation. As a result of differentiation the earth was
5
divided into three major layers viz., crust, mantle and core. A. core83%, B.
mantle 16%, C. crust 0-5 % (fig).
The layers of the earth crust are distinguished by their
a. thickness and depth
b. density and temperature
c. Metallic content and rocks.
The most abundant continents of the earths crust are igneous rocks.
The top most layers of the earth which forms the crust of the earth is the
lightest layer. The outer crust of the earth is made up of continents. These
continents are mainly composed of sedimentary rocks.
There are two types of crust
1. Continental crust
2. Oceanic crust
The continental crust is thicker below the mountains than below the
plains. The continental crust is largely granites and supports the continents. It
is an average of 32km to 40km thick although it can be more than 60km thick
at mountain ranges. The oceanic crust is made largely of basalt and gabbaro
and is 5-16 km thick. The main part of the crust consists of igneous rocks, the
rest consists mostly of sedimentary and metamorphic rocks (Fig).
6
3%
3%
3% 2%
4%
5%
8%
45%
Oxygen
Silicon
Al
Fe
Ca
Na
K
Mg
Others
27%
The graphic presentation of the percentage of element
in the earth crust.(fig)
Rock as the members of the earth crust.
The earths atmosphere consists of gases completely enveloping to a
height of about 150km. The hydrosphere includes sea, lake, stream and
underground waters. Lithosphere is the hard crust of the earth consisting of
rocks and rock minerals. Rock plays an important part in geography. They
influence the different types of land forms and various types of minerals are
associated with them. They are used for construction and several other
purposes. Agents of weathering i.e., disintegration and decomposition of
rocks and rock minerals followed by pedogenic factors and processes change
them into soil, which is the basis of both plant and animal life.
A rock is any mass of the harder portion of the earth crust. Rocks make
up most of the solid materials of the lithosphere. The substances of which
they are made are called minerals. A rock has no definite chemical
composition. It is usually a mixture of various materials. Where rocks contain
compounds of metals of sufficient value to be mined, they are called ores.
Ores are often found in mountainous districts where folding or fracturing has
brought ore bearing rocks to the surface. Ores often occur in veins or seams
that may vary from a few inches to many feet in thickness. The rock structure
can be seen in railway and road cuttings, in quarries and other excavations, in
mines, wells and borings.
7
The continental part of the earth's crust is composed of many different
kinds of rocks. A rock is any mass of the hard portion of the earth's crust.
Rocks make up most of the solid materials of the Lithosphere.
A rock is any mass of natural deposit, which forms the solid part of the
earth's crust. As such a rock may be hard like Granite or soft like Clay and
Sand. It may be porous; like Chalk or non-porous like Granite, Slate & Clay.
The porous rock permits water to penetrate through them, while the nonporous rocks are impermeable to water. It must be borne in mind that a rock is
not a chemical compound, but a conglomeration of a large number of
minerals, although these minerals are formed in their turn by the aggregation
of a large number of chemical elements. A rock may be defined as an
aggregate or assemblage of one or more minerals. The lithosphere is
composed of more then 90 elements, but only 14 form the bulk of earth's
crust. They are O2, H2, C, P, S, CI, Si, AI, Fe, Mn, Mg, Ca, K & Na. with; a few
exceptions. These elements are combined in the form of minerals. The
minerals occur as separate bodies or as natural aggregates called Rocks.
Rocks are aggregates of minerals and the basic units constitute the earth's
crust. The commonly found minerals in the rock are feldspar and quartz. The
metal compound of rocks is known as 'Ores'.
Many rocks are composed; of only one type of mineral called monomineralic rock. In such cases, the rock is also known by the name of the
minerals. But a rock composed of various types of mineral is only known as a
rock. These minerals were present in the earth when it was in molten or
gaseous condition and crystallized in the form of rocks as the earth cooled.
Granite contains crystals of feldspar and mica. Set in hard-mass quartz. Many
decomposed fragments of all types of rocks form the stony sub soil which lies
over the underlying rocks. These rocks throw light on the past history of the
earth and form the basis of the present landscape.
Depending upon their genesis and structure i.e. origin and mode of
formation, occurrence and physical properties, three main groups of rocks are
recognised.
1. Igneous: - cooled molten rock.
2. Sedimentary: ... sediments deposited in water and consolidated (made into
hardened mass of rock).
3. Metamorphic: - igneous or sedimentary rock changed by heat or pressure
(hardened or changed mineral orientation) or chemical solution.
Rocks that are derived from igneous rocks are called ortho
metamorphic rocks. E.g. Gneiss, schist. Rocks that are derived from
8
sedimentary rocks are called Para metamorphic rocks. E.g. Marble, slate,
Quartzite.
Types of rocks:
Rocks are composed of minerals. Some of the rocks are;
monomineralic. E.g. Dunite or Olivine rock is made up of one mineral, But
most of them contain two or more minerals.
Primary rocks are those which are supposed to be formed first in the
earth's crust. eg. Igneous rock. Secondary rocks are those which have formed
due to weathering and compaction, or metamorphosis of primary rocks. e.g.
Sedimentary and Metamorphic.
Rocks
Igneous Rock
Sedimentary Rocks
Metamarphic Rocks
Hydro (water)
Formed
Formed
Formed
Extrusive
Intrusive lava or voleanic mechanically chemically organically
or clastic
e.g. Gypsum e.g. peat
rock
rock e.g. shale
Limestone coal
Dynamo
(pressure)
Thermal
(Temp.)
Plutonic Dyke or
rock
Hypalyssal
rock
Dynamothermal
(Pres & heat)
1. Igneous rock:Are formed by the cooling solidified and crystallization of molten earth
materials called Magma from the interior of the earth. Magma is complex, very
hot solution of silicates containing water and several gases. It originates in the
deep interior of the earth's body in the upper mantle. Magma moves upward
by melting away the overlying rocks and by forcing them aside. This process
is termed as 'intrusion'.
•
Also called as primary rock or king of rocks or parent rock because it is
from these that the other rocks have been derived.
•
Ancestors of all other rocks and make up 85% or more of earth's crust.
•
Magma that reaches earth's surface and then solidified is called 'Lava'
e.g. Feldspar, granite, basalt, gablaro, pumice, scoria.
9
•
Platinum, diamond, iron, silver, gold, copper, manganese, lead and
zinc are found in igneous rock. Fossils, coal and petroleum are never
found in igneous rocks.
•
Igneous rocks are generally hard and water percolates through them
with difficulty along the joints.
•
Since water does not percolate easily these rocks are less affected by
chemical weathering.
•
These rocks are non-fossiliferous.
•
Most of the igneous rocks consist of silicate minerals.
Igneous rocks are formed due to the cooling and solidification of molten
materials of the earth's crust. The rocks of the earth are in molten stage at a
depth ranging from 16 to 20 km and are known as Magma.
The chief characteristics of igneous rocks are that they are found in
masses and not in layers. So they are called 'unstratified rocks'. These rocks
now appear on the earth's surface over small areas e.g. Brazil, Table land of
Africa, Western Australia, N.E Canada and the Deccan of central India. The
black soil of Deccan also called the Deccan Trap consists of Basalt rocks.
The different types of igneous rocks have got different elements in
varying proportions. Roughly they may be said to conform to anyone of the
following four consumptions:
1. Peridotite is the crystalline rock consisting of Ferro magnesium,
silicates and oxides. Peridotite shell refers to the mantle of the earth.
2. Basalt, diorite and tachyite: the names given respectively to the
crystalline, semi-crystalline and glassy forms of a rock which consists
of lime, Ferro magnesium silicate and reduced proportion of iron
oxides.
3. Alkali rocks- in which alkalis predominate in place of alkaline earth and
Ferro magnesium silicates. Its various forms are; Diorite, Porphyrite
and Andesite.
4. Silicon rocks- contain more of silica but less of iron, lime and
magnesium. Tonalite is the crystalline form of this type quartz
Porphyrite is the semi crystalline form and dacite is glassy.
But the commonest classification of igneous rock according to their
chemical composition is into 1) Acidic igneous rock and 2) Basic igneous rock.
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1. Acidic igneous rocks:
•
They; are light rocks contain 65-80 % SiO2 and 20% divided over AI,
alkalis, iron oxide, magnesia and lime.
•
belong to the portion of the earth known as SIAL, they contain less of
the heavier minerals like Fe and Mg. pale in color, contains feldspar
(aluminum silicates of Na, K & Ca)
•
Compact and massive hard and resist weathering.
•
On disintegration form coarse sandy soil, low fertile soil is formed.
•
High mountains are formed of acid igneous rocks. E.g. Granite,
syenite, diorite.
2. Basic Igneous Rocks:
•
Contains less than 40% SiO2 ,40% Magnesia(MgO) and 20% iron
oxide, Little lime, Little AI, and no alkalis.
•
They are dark colored due to the predominance of ferro-Magnesium.
•
They are relating to the portion of SIMA. They are soft and weather
easily eg. Gabbaro, Basalt, Peridotite, Dolesite. The molten lava flows
and spreads to far of distances and plateaus and formed from these
rocks.
•
On disintegration form fine texture soil, high fertile soil with favourable
chemical characteristics.
•
The common igneous rocks found in India are the granites (acidic) and
basalt or the Deccan trap (basic).
•
Feldspars and ferro magnesium minerals which form the bulk of most
of the igneous rocks are very much susceptible to decomposition. Ores
of metals valuable to man are often associated with igneous rocks.
Classification on the basis of situation:
(Mode of occurrence)
On the basis of mode of occurrence, igneous rocks are classified into
two major groups.
a) Intrusive Rocks: (Plutonic Rocks)
When the rising Magma is cooled and solidified below the surface of
the earth they are known as intrinsive rocks. Sometimes the molten matter is
not able to reach the surface and instead cools down very slowly at great
11
depths. Slow cooling allows big sized crystals to be formed. Granite is a
typical example. These rocks appear on the surface only after being uplifted
and denuded. Denudation or earth movements may bring plutonic rocks to the
surface when they often form infertile areas, Such as Dartmoor - England.
They are also called plutonic rocks e.g. Granite. They are found as batholiths,
laccoliths, lopoliths, phacoliths, sills, dykes, and necks. They result from the
cooling of magma very deep inside the earth. Due to very slow cooling at the
great depth large grains are developed e.g. Granite, coarse grained dolerite.
The cooling is slow because of great heat at depths and crystals formed are
large. Intrusive rocks are formed deep underground where Magma is forced
into cracks or between rock layers to form structures such as sills, dykes and
batholiths. The magma cools slowly to form coarse grained rocks such as
gabbaro, pegmatite.
b) Extrusive igneous rocks: (lava or volcanic rock)
Extrusive rocks are formed above the earth’s surface from lava
(magma that has been ejected in a volcanic eruption). The molten lava cools
quickly producing fine grained rocks such as rhyolite, and basalt. These are
formed by rapid cooling of the lava thrown out during volcano eruptions. Rapid
cooling prevents crystallization as a result such rocks are fine grained. Basalt
is a typical example. The Deccan traps region in Peninsular region is of
basaltic origin.
2. Hypabyssal or Dyke rocks:
These rocks occupy an intermediate position between deep seated
bodies and surface lava flow. They are formed when magma cools and
solidify beneath the earth surface. They take different shapes and forms
depending upon the hallow places in which they solidify. These deep seated
intrusions are known as plutonic rocks. Highly coarse grained granite is a
typical example of plutonic rocks. The granite of various colors - grey, red,
pink or white is found on the deccan plateau of south India. In Madhya
Pradesh, Chota Nagpur, Rajasthan and in parts of the Himalayas. During its
molten state within the earth, it contained water, steam and various gases,
Which escaped on solidification of the material It is used largely as a building
stone and many ancient monuments like temples are made of granite rocks
(Granite City - Abrdeen, Scotland).
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b. Discordant intrusive body:
The intrusive rocks are characterized by the development of a variety
of forms depending upon their exact mode of formation and relation with the
surrounding country rocks. If an intrusive mass happens to cut across the
structure of the pre-existing rocks of the country, it is said to be discordant
body. The intrusive igneous body cut through the bedding or foliation of the
country rock. (Foliation refers to parallel orientation of platy minerals or
minerals banding in rocks). It is said to be unconformable that is in which
parallalism bedding or structure is absent. Discordant is the term used for
describing an igneous rock which shows cross cutting relationship to bedding
or foliation.
D - Discordant body within the country rock (ordinary rock)
c. Concordant intrusive body
Intensive mass happens to run parallel to the structures of the country
rocks in which they occur it is said to be concordant body (fig).
C - is the concordant body with the country rock.
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Intrusive body is lying parallel with the bedding structure that is
structurally conformable. Concordant rock bodies necessarily run parallel to
the structures of the country rocks in which they occur. If the country rocks be
made up of sedimentary beds, a concordant mass should run parallel to the
bedding planes while a discordant body must penetrate through them. In case
of metamorphic rocks, forming the country rocks the concordant body must
run parallel to the foliation or lineation of the country rocks while the
discordant masses should cut them through. (lineation refers to anyone
dimensional feature in a rock or shown on a rock surface). If the pre-existing
country rock itself is made up of igneous rocks all other subsequent bodies of
igneous origin in that region are likely to be discordant in nature, since the
igneous country rock does not ordinarily exhibit any characteristic feature to
which the later injection may run parallel.
2. Extrusive Igneous rocks: (Volcanic rocks)
The extrusive rock bodies like the lava flows come upon the surface
and appear to have spread themselves in the form of sheets.
Extrusive or volcanic rocks 1 and 2 lava flows.
Volcanic rocks are formed in the surface either by the consolidation of
the lava or by the accumulation of volcanic fragments. This igneous rocks are
formed by the cooling and solidification of molten lava on the earth surface
Eg. Bassalt, Gabbaro, andesite trachyte, Rhyolite, Obsidian
These are generally fine grained or glassy because of quick rate of
cooling of lava. The extrinsive igneous rocks are divided into two sub groups.
14
I. Explosive eruption type or Central Eruption type
Volcanic materials of violent volcanoic eruptions include bombs eg. Big
fragments of rocks, lapilli (Pea sized fragments) and volcanic dust and ashes.
II. Quiet eruption type or Fissure eruption Type
In this lava appears on the surface through cracks and fissures and
their continuous flow form extensive lava plateaus volcano.
E.g. Deccan plateau, Columbia plateau (USA)
The Laki fissure eruption in Iceland 1783
Quiet volcanoes discharge liquid basic lava with little gases and no
solids. This lava is basaltic in composition containing little silica, hence gives
rise to dark coloured basic rocks. The cone of quiet volcano is very gentle,
because the molten lava flows and cover extensive areas forming traps.
E.g. Deccan Trap.
Sedimentary rock
Sedimentary rocks make up only almost 5% of the volume of the earths
crust. These rocks are so important that they spread over 75 % of the present
area of the land.
Earth’s
crust
5%
Sedy. rock
95%
Igneous +
metamorphic
rock
Sedimentary rocks or secondary rocks or county rock or soft rock are
those which have been formed by the agency of the water, wind and ice.
These agents break and erode the igneous rock, transport these broken rock
fragments and deposit them at other places. Sedimentary rocks are formed
w\hen sediment becomes compressed and cemented together in a process
known as Iithification. The deposit of the material often occurs in the form of
15
layers or strata and therefore they are known as sedimentary rocks or
stratified rocks. The sediments is usually deposited in layers one over the
other. The weight of the upper layers hardens the underlying layers. These
layers become hardened, stratified and consolidated. Sedimentary rocks often
contain alternate layers of sand clay and silt which are deposited by water and
the layers become compressed and consolidated by the cementing action of
silica. The unconsolidated loose deposits such as sand are also sedimentary
rocks.
Sedimentary rocks are prone to folding and faulting. Due to
compressional and tensional forces. In sedimentary rocks each layer exhibits
differences in composition, texture, hardness, cohesion or color. Single layer
is called bed, stratum or sediment.
The plane of function of two successive layers is called bedding plane
or divisional planes. A single layer is bounded be two bedding planes.
Thickness of individual beds may vary from many meters down to few mm. If
the bed is very thin (in mm) it is called Lamina. Bed or stratum also refers to
the smallest litho stratigraphical division,
Bed
Bedding plane
Bed
Most of he sedimentary rocks are permeable and porous but a few of
them are also non porous such as clay. Shale is the most abundant
sedimentary rock.
The sedimentary rocks are non crystalline have fossil of plant and
animals - water enters through the rocks due to their porous naturecompressed of all sizes of particles fine, small and big- much sifter than
igneous and metamorphic rocks- because they are soft rocks. These are
easily eroded.
Classification
1. Mechanically formed sedimentary rocks- clastic rocks.
2. Wind deposited sedimentary rocks- Aeolian rock e.g. Loess
3. Glacial deposited sedimentary e.g. Moraines, sand and gravels and
bouldery clay or silt.
4. River deposited sedimentary rock- Riverine rock e.g. Clays, alluvial
occur in flood plains.
Alluvial, glacial and Aeolian deposits from the unconsolidated
sedimentary rocks.
16
Lakes deposited sedimentary rock.
Lacustrine rock. E.g. silt (unconsolidated lacustrine rocks)
The western ghat range is said to have been formed due to differential
erosion of Deccan plateau made up of lava flows hence consist of
sedimentary rock.
The Himalayas is made up of sedimentary rocks since they contain sea
fossils young told mountains.
The Eastern Ghats on the other hand, represents the remnant of a very
ancient plateau made up of metamorphic rocks.
The Vindhyan range of mountains is made up of sedimentary rock.
Old told mountains are pennines chain (England), Applachian (North
America) cape range of south Africa, Great Dividing range of Australia.
By compaction - sand stone (from sand)
By cementation- shale from clay
Conglomerate and breccia
Conglomerate – this is formed due to consolidation of rounded pebbles
or special bodies or gravels with some cementing materials which may be due
to silica, iron oxide, or calcium carbonate.
Breccia
This is composed of angular fragments of disintegrated rocks by some
cementing material. They are formed from the material such as tallus or scree
accumulating at the foot of slopes in semiarid, desert or cold regions and this
is due to mechanical disintegration.
Chemically formed sedimentary rocks (non clastic rocks)
Rock salt (Nacl) by Gypsum
Nitrates and potash
17
The rocks which are either mechanically or chemically formed are
called inorganic sedimentary rocks because they are mainly formed of mineral
matter.
Organically formed sedimentary rocks (Non-clastic rocks)
a) calcareous sedimentary rocks- formed from the skeletons of sea
organism (oysters, mollusks cockIed etc.) chalks, talc, dolomite, lime stone,
aragonite (CaCO3) siderite (FeCO3) magnesite (MgCO3).
b) Carbonaceous sedimentary rocks - formed due to decomposition of
dense swamp vegetation below the surface and seafloor
c) E.g. coal. Peat lignite petrol, rock oil
The sedimentary rocks contain fossils. These fossils are the petrified
remains of animal and plant life that lie enclosed between the two layers.
These formation fossils throw interesting light on the place and time of their.
Sedimentary rocks serve as sources for many ores, buildings stones
(Sand stones), coal raw material for cement, petroleum reserves.
Conformity and unconformity
Sedimentary rocks are laid down in layers called seds or strata. Each
new layer is laid down horizontally over older ones. There are normally some
gaps in the sequence called unconformity. These represent periods in which
no new sediments were being laid down or when earlier sedimentary layers
were raised above sea level and eroded away.
Conformity
Strata deposited during a period of sedimentation are conformable or
concordant when the stratified deposits occur as regularly and continuously
laid beds, a layer after layer, without any change in the general parallel
arrangement. The structure then produced is known as conformity or
conformability.
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Unconformity
When the beds after one period of sedimentation, have been lifted up
deformed, eroded and again submerged to serve as the floor for a new
deposit the new series of strata will be lying unconformably or discordantly
upon the old series. Then the structure produced is known as unconfermity.
Unconformity indicates that there is no connection between the sedimentation
of the first and the second period and that there were deposited in two
independent seas or layers during two different periods
(unconformable )
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Overlap
When the upper beds of the sedimentary formation extend over a wider
area than the lower beds of the same series, the structure then produced is
known as overlap. This structure is developed as a result of submergence of
land or invasion of the sea. The subsidence of a region below sea level is
known as a submergence of a land or transgression of sea. The retreat, of
sea is known as marine regression or an emergence of a land.
Metamorphic rocks
Metamorphic rocks are formed from the subsequent transformation of
igneous and sedimentary rocks under the influence of high temperature
thermometa morphism) and chemically active liquids i.e. water (Hydrometa
morphism) and gases. The changes occur in colour, hardness, structure,
texture and mineral composition in rock fragments of the pre-existing rocks
through temperature and pressure. The pre-existing rocks may be igneous,
sedimentary or even metamorphic rock and the process is called
metamorphism. Rocks that are derived from igneous rocks are called ortho
metamorphic rock
Egg. granite
- gneiss
Mica
- schist
Basalt
- slate
Rocks that are derived from sedimentary rocks are called Para
metamorphic rocks
Eg.
sandstone
- Quartzite
Limestone
- Marble
Shale
- slate
Peat
- coal
Slate
- Phyllite
Thermal metamorphism or contact metamorphism
20
The metamorphism caused by high temperature is called thermal
metamorphism.
The type of rock formed in this process is known as recrystallized rock.
Eg.
shale
- slate
Coal
- graphite, anthracite
Dynamic metamorphism or stress metamorphism
Rock changes taking place under high pressure is known as dynamic
metamorphism. The pressure force acts due to various reasons in the interior
of the earth as well as in the crust
Eg.
coal
- graphite
Most dynamic metamorphism is associated with fault (fractures alogn
which movement has occurred) zones where rocks are subjected to high
differential pressures. The metamorphic rocks resulting from true dynamic
metamorphism are called Mylonites and are typically restricted to narrow
zones adjacent to faults. Mylonites are hard, dense, fine grained rocks, many
of which are charaterized by thin laminations.
Regional Metamorphism
In this case(Recrystallized rock) masses of igneous or sedimentary
rocks lie buried deep in the ground. The pressure of the layers lying above
them and the high temperature produced there from effectively change them.
The mountain building movements bring above it a general flow in and over
them as a result, the rocks submerged are completely transformed and
become crystalline. Such rocks as were originally crystalline are recrystallized
and the whole thing becomes massive and compact. The earth movements
bring them underground and again it is the movement of the earth that bring
them back to the surface after they have been hardened and cooled. The
fossils of the original sedimentary rocks are destroyed by heat and pressure.
Hence, fossils are not likely to be found in these rocks.
The formation of metamorphic rocks takes place always in the solid
state. Valuable minerals such as gold and silver are associated with them.
Some rocks after metamorphism become harder than their original form.
e.g. marble from Limestone
Diamond from carbon
When already formed metamorphic rocks are again metamorphosed
they are known as remetamorphosed rock. Slate 150o-200oc phyllite.
21
When temperature and pressure affect a large area and change the
rocks, it is called regional metamorphism.
Eg. Sandstone - Quartzite
Rock Cycle
Weathering and erosion
deposited
Sedimentary rock
Igneous
Pressure + Temp +
Liquid
Melt under high temperature
Magma
Metamorphic
The global geological cyclic movement of lithospheric rock material in
the course of which rock is created, destroyed and altered through the
operation of internal and external earth pressures.
Secondary rocks are formed by physical disintegration and chemical
decomposition. Physical disintegration gives rise to detritus of coarse grains.
Decomposition produces mineral of flour like fineness. The amount of
transport also affect grain size – longer the transport, finer the grain size,
chemical decomposition includes oxidation, hydration, carbonation and
solution.
22
MINERALOGY
Mineralogy – that branch of geology which deals with the study of
minerals.
Nature is divided into three kingdoms via. Animals, vegetation and
minerals.
Minerals are naturally occurring elements and a compound making up
the solid part of the earth’s is crust. A mineral is a naturally, occurring
homogenous inorganic solid substances having distinctive physical properties,
usually a regular internal molecular structure and a more or less definite
chemical composition. Most of the minerals are crystalline.
The rocks that form the earth's crust are composed of aggregates of
minerals. Most of the minerals are crystalline. Some minerals lack a
systematic arrangement of atoms and do not have fixed compositions, these
are called Mineraloids and because they do not have crystal substances, they
are said to be amorphous (without form).
These minerals are specifically referred to the rock forming minerals.
Many minerals have a tendency to form crystals which are bounded by plane
surface arranged in a regular and symmetrical manner. Some physical
properties like cleavage, specific gravity or color are useful in the identification
of minerals, usually minerals are composed of two or more elements. But
some minerals have only one element for instance graphite, gold, sulphur
etc., are called one element minerals. Most of the minerals are oxides,
silicates and carbonates, coal and petroleum, though of organic origin, are
also included among minerals. Almost all minerals are solids. The only
exception being mercury, Water and mineral oil (petroleum).
Chemical composition
The most prominent and common elements forming the minerals and
thus the crust of the earth are:
Oxygen 48 - 50%
Silicon 24 - 25%
Alumina 14%
Potassium
Sodium
Calcium
Iron
Magnesium
Titanium
_____in varying percentage in different minerals
23
Minerals are formed due to fusion solution and sublimation form vapor.
The process of formation of a mineral may be magmatic, or sedimentary or
metamorphic.
Rocks are the mixtures of minerals. The properties of rocks therefore,
depend upon the mineral present in them. The rocks found in the earth's crust
are classified in to 3 groups i.e igneous, sedimentary and metamorphic.
Broadly the minerals may be classified as:
1. Minerals of economic value are found to be useful to society.
e.g. Hematite is mineral of economic value
2. Rock forming minerals-those minerals which are important only
in so far as they are consistent in the rocks. The mineral biolite
(Black mica) is a typical example of rock forming mineral.
The rocks forming the crust of the earth constitute the store house of all
kinds of minerals. The principal minerals in the earths crust are
Feldspar - 57.8%
Amphibole, Pyroxene – 16%
Quartz – 12.7%
Mica – 3.6
Accessory mineraly in varying amounts.
General Classification of Minerals
Metallic
Ferrous
E.g. Iron ore
Pyrite
Tungsten
Nickel, cohalt
Non-Metallic
e.g. Limestone
Nitrate
Potash
Mica
Non-ferrous
Gold, Silver,
Copper lead
Energy
E.g. Coal
Petroleum
Atomic minerals
E.g. Thorium
Bezyllium
Lithium
Classification of rock forming minerals or soil forming minerals.
The soil contains rock forming minerals either primary or secondary in
nature.
24
Relationship of minerals with soil
When most of the minerals undergo the process of weathering they
produce the important mineral nutrients essential for soil (like Ca, K, P, Fe,
Mg) form feldspar, mica, Hornblende etc. The important reactive part of the
soil viz, clay is derived from the clay minerals which is very important in the
life of soil in holding the nutrient moisture, gas etc.
Apatite minerals give out either organic or inorganic P though in small
quantities.
P – Apatite mineral
-Trace elements like Fe etc. from concerned minerals
K- Mica mineral
Ca – from calcite
Clay – feldspar
Mg – from Dolamite
Quartz, though resistant to decomposition on constitute 40-70% of soil
(sandy soil) and enhances the physical properties of soil for aeration,
drainage, percolation etc.
One type of classification of rock forming minerals is based on mineral
constituents in rocks.
1. Silicate soil forming minerals
Feldspar, amphiboles and pyroxene
2. non silicate soil forming mineral
Calcite, magnesite, gypsum, dolomite
Another classification - based on structure and composition of rocks.
1. Primary minerals
2. Secondary minerals
3. Accessory minerals ,
Primary minerals
Are those which crystallise directly form magma or lava at elevated
temperature and inherited from igneous and metamorphic rocks are of
primary origin.
Primary minerals found in the rocks are the original source of the
primary minerals found in soils. The most abundant are quartz and feldsar
with relatively small portions of pyroxene, amphiboles, olivines, micas etc. The
primary minerals in soil are mostly concentrated in the coarse fraction.
Feldspar forms the largest part of the soil forming mineral or rock forming
mineral. The soil forming mineral contributes as potential source of plant
25
nutrients. Feldspar and ferromagnesium minerals which form the bulk of most
of the igneous rocks are very much susceptible to decomposition.
Feldspar - chemically more active antydrous alumino slicates of K, Na
& Ca. ex. Potassium feldspar, sodium feldspar and lime feldspar. These are
hard, weather slowly or moderately but provide important nutrients and clay in
the weathered products.
1. Potash feldspar K20 Al203. 6Sio2 orthoclase
2. Soda feldspas Na20 Al203. 6Sio2 Albite, sodium rich plagioclase
3. Lime Felspan cao Al203. 6Sio2 Anorthite calcium rich plagioclase
2&3 are called plagioclasic feldspar or oligoclase.
Mica - muscovite - white or potassium mica
Biotite black mica or Fe-mg mica
This is the important source of K and clay.
Glitter in rocks or wet sand. Ferro magnesium minerals are generally
dark colored. Silicate minerals containing iron and magnesium and including
olivine and pyroxene.
Magnetite, chromite, microcline, olivine, pyroxene, plagioclase,
orthoclase muscovite, biotite amphibole, Hornblende, Quartz are common
constituents of igneous rocks of different types.
Primary minerals can further be divided in to essential minerals and
accessory minerals.
1. Essential minerals
Its presence is used in the definition or naming of rocks. Ex. Quartz,
feldspar, Mica.
2. Accessory minerals
Occur only in small quantities in soils and rocks its presence is not
used in naming of the rock, whose presence or absence does not affect the
characters of rock. Ex. Sphene, apatite, zircon.
Ex. Quartz and feldspar are the essential minerals of a granite rock
while zircon, sphene, apatite are the accessory minerals. An accessory
mineral in one rock can be an essential mineral in another rock.
Secondary minerals:
•
Results from the alteration of primary mineral
26
•
Are formed at low temperature reactions
•
Inherited from sedimentary rocks or formed in soils by weathering.
•
e.g.: calcite CaCO3; dolomite Ca Mg(CO3)2; quartzite silica cemented
sands clay- secondary mineral synthesized from the residual products
of weathering.
The particles <2microns (0.002mm) is arbitrarily called the clay fraction
which possesses colloidal particles.
A mineral primary in one rock can be secondary in other rock, for
example quartz is a primary mineral in a granite rock, but occur as a
secondary mineral when liberated as a result of alteration of several rock
forming minerals in basalt.
PROPERTIES OF MINERALS:
Each mineral is generally characterized with a set of qualities, some of
which are always distinctive and differentiate it from the other minerals. Some
of these minerals are studied from the body of the mineral.
Physical Properties of Minerals
Color, luster, form, hardness, fracture, cleavage, streak, specific
gravity, transparency, magnetism.
1. Color:
The color of a substance is its appearance in light and depends upon
the composition and the structure of the substance.
In minerals, colors may be either of 'inherent' or of an 'exotic nature'.
The former is related to the chemical composition and is more diagnostic
whereas exotic colors are due to small traces of impurities and may vary
within wide limits.
2. Lustre:
The way in which a mineral reflects light from its surface and may be
called the ‘shine of the mineral’. It varies with the composition and reflecting
power of the mineral surface.
Lustre is distinguished as
•
metallic - like that of a polished metal surface
•
vitreous - like that of a broken glass
•
resinous - like that of a yellow resin
•
pearly - like that of a pearl
27
•
greasy - as if the surface were covered with a film of oil
•
adamantine - having the brilliance of diamond
3. Form:
The natural form of a mineral such as amorphous, crystalline, crypto
crystalline (too small crystals to be identified with an ordinary microscope i.e.
mere traces of crystalline structure) amorphous - complete absence of
crystalline structure), bladed, flaky, botryoidal (resembling grapes closely
bunched), columnar, prismatic, nodular, dendritic, granular.
4. Streak:
The streak is a thin layer of powdered mineral made by rubbing a
specimen on a non-glazed porcelain plate. A porcelain plate is used for
determining streak. This is known as streak plate. This is the color of a
mineral in powder form, very often mineral will have a different colors in
powder form.
•
hematite - red
•
magnetite - black
•
Talc – White
•
Chromite – light brown
5. Hardness:
This is one of the most noticeable ways in which minerals differ. Refers
to the relative resistance of a mineral to scratching.
For determining hardness, German mineralogist Fredzrich Mohs
designed a scale of standard minerals, known as Moh's Hardness Scale,
Which is given below. The scale comprises the minerals arranged in order of
ascending hardness; the softest is assigned a value of 1 and the hardest
value of 10. Hardness of any mineral lies in between these two limits
S. No.
1.
Minerals
Talc (Hydrous - Mg- Silicate)
Hardness
1
2.
Gypsum
2
3.
Calcite
3
4.
Fluorite
4
5.
Apatite
5
6.
Orthoclase
6
28
7.
Quartz
7
8.
Topaz
8
9.
Corundum
9
10.
Diamond
10
The box in which these minerals are kept is known Moh’s Harness box.
Determination of Hardness:
1.0-2.0------scratched by finger nail
2.5-3.0------scratched by copper coin
3.5-4.5------scratched by pen knife (5.5)
5.0-6.0------scratched with difficulty by pen knife but easily by glass
6.5-----------scratched with difficulty by glass but easily by file
7.0-10-------scratched by glass but not scratched by file
7.0-----------scratched streak plate
6. Cleavage:
It is defined as the tendency of a crystallized mineral to break along
certain definite planes yielding more or less smooth surface.
The surface along which the mineral breaks is the cleavage surface.
Cleavage is usually described as poor, fair or good according to how smooth
a cleavage surface is produced.
The cleavage planes may resemble crystal faces
•
Are always parallel to some faces of the crystal form typical of the
mineral.
•
e.g. cubical cleavge, Octahedral cleavage, prismatic cleavage
•
only crystalline substances have well defined cleavages
7. Fracture:
The appearance of broken surface of a mineral is expressed by the
term fracture. It is essential that fracture is studied in the direction other than
29
of cleavage. Common type of fractures are even, uneven, conchoidal,
splintery hackly, earthy.
8. Transparency:
•
Transparent- when the light can be transmitted through it (seen
through)
•
Translucent- when light can be transmitted through it, but can not be
seen through.
•
Opaque: when no light is transmitted through the mineral
9. Specific Gravity:
•
Is the ratio of the weight of the mineral in air to that of an equal
volume of water.
Weight of mineral in air
S.G =
Weight in air - weight in water
Specific gravity can be approximated by comparing different minerals
held in the hard. Metallic minerals such as galena feel heavy where as nearly
all others feel light.
10. Tenacity:
Indicates the strength of the mineral. E.g. Brittleness (easily broken),
flexibility, elasticity, malleability, etc.
When a mineral can be cut out from it with knife, it is termed as sectite.
If the cut piece can be flattened under a hammer it is called malleable; flexible
- bend under pressure; elastic - remain in original shape when pressure is
released.
11. Structure:
A definite and characteristic arrangement in its outer appearance or
physical shape. This shape is expressed by term structure and is typical in the
case of many minerals.
Some examples are,
a) Fibrous - made up of filres, e.g. Gypsum, Asbestos
b) Columnar - mineral is composed of thin or thick columns, sometimes
flattened, e.g. Hornblende
c) Bladed - composed of thin blade like parts, e.g. Kyanite
d) Lamella - the plates or leaves are separable, e.g. Vermiculite, Chlorite
30
e) Granular - the mineral shows numerous grains packed toghather, e.g.
chlorite, dolomite
f) Globular or Botryoidal - the mineral is in the form of bulbous
overlapping projections, e.g. Haematite, etc..
g) Botryoidal for an aggregate like bunch of grapes, e.g.Psilomelane
h) Dendritic - for tree like or mass like form, usually produced by
deposition of minerals from solutions by capillary action. E.g.
Manganese oxide
GEOLOGICAL
EXPRESSION
STRUCTURES
AND
THEIR
TOPOGRAPHICAL
Though there are hundreds of minerals, only a few of them are of
common occurrence as rock forming minerals. The rocks themselves
constitute the store house of all kinds of minerals. The rock farming minerals
as well as those of economic value are all to be found within the three
categories of rocks namely igneous, Sedilmentary and Metamorphic rocks.
The different rock types are characterized by their own typical mineral
assemblages, stated otherwise, minerals have a tendency to occur in some
definite groups.
The characterstic mutual association of minerals in specific groups is
called ‘PARAGENESIS’.
Minerals as common constituent present in igneous rocks: Quartz,
Ordthoclase, Plagioclase, Microcline, Muscovite, Biotite, Amphilboles,
Pyroxenes, and Olivines.
Minerals found in Metamorphic rocks:
Kyanite, SiIimanite, staurolite, Andalusite, chlorite, Garnet etc,
Sedimentary rocks are the products of weathering of the pre existing
rocks and hence they contain any mineral or assemblage of minerals i.e ...
Depends upon the sediments.
DESCRIPTION OF MINERALS GROUPS:
1) Rock forming silicate minerals;
a) Silica group (quartz)
b) Feldspar group
c) Mica group
d) Pyroxene group
31
e) Amphibole group
f) Olivine group
g) Garnet group
2) NON SILICATE GROUP
a) Carbonates - Calcite and Dolomite mineral group
b) Sulphates and Chlorides - Evaporites
c) Oxide of iron mineral
Topographical expression deals with CRYSTOLLOGRAPHY
Crystallography deals with the study of crystals, with reference to their
formation from the melts, internal structure& external shape or morphology. A
crystal is defined as a regular polyhedral form bounded by smooth surface
known as FACES.
Crystallography; the scientific study of crystals, it includes not only
nature, but also cause of their atomic structure.
A) SILICA GROUP-QUARTZ (SIO2)
About 8%of the earth crust is made up of silicates and the free silica.
Next to feldspars, this is the most abundantly occurring mineral of the earth
crust. It is colorless or white when pure, but many colored varieties occur, the
colors being due to traces of impurities. It occurs in all kinds of rocks Le.
Igneous Sedimentary and Metamorphic.
Harder than feldspars and cannot be scratched by knife, its hardness is
7.
The fundamental unit is Silica-oxygen tetrahedron represented by the
formula (Si04)4-. In this tetrahedron the very small si4-ion is situated in the
centre and ils surrounded on the 4 sides by relatively big (5 times big) Oxygen
atom.
Silica is centrally spaced and it is surrounded by 4 anions 0-.
32
The distance between the silica atom at the centre and the oxygen
atom at the corners is 106OA. This fundamental unit is repeated linked in
different ways giving rise to different types of silicate structures.
B) FELDSPAR GROUP
These are the most abundant of all the silicate minerals. The most
abundant mineral in igneous rocks, consisting structurally of a complex
aluminum silicate frame work with varying proportions of potassium sodium
calcium and rarely barium.
Feldspar are grouped in to alkali feldspars ( k41si308, NaAlsi308 ) and
plagioclase feldspars (NaAl Si308, caAlsi308) And are monoclinic or triclinic
minerals.
Monoclinic System
Crystals belonging to the monoclinic system Possess three unequal
crystallographic axis a, b&c axis is always vertical. The inclined ax is a axis. It
is known as clino axis. The longer horizontal axis b axis. It is referred as
orthoaxis. Orthoclase feldspar division of minerals crystallizes in monoclinic
system.
Vertical
c
a
Ortho b
b’
Clino
a’
c’
33
Triclinic System
The crystals of this system consist of 3 Crystal to graphic axis all of
which are essentially unequal in length and inclined at various angles. Crystal
with un equal axes all of which are inclined to one another.
c
a
Vertical
b
Ortho
b’
Clino
a’
c’
The plagioclase division of feldspars crystallizes only in triclinic system.
Feldspars are classified both on the basis of their chemical composites
and also on their mode of crystallization.
The minerals albite (Na AISi308) and Anorthite (ca Alsi308) are
Isomorphous and their solid solutions give to the plagioclase feldspar series
crystallizing in the triclinic system.
Isomorphism:
It refers to the property by virtue of which different compounds but with
allied chemical composition are capable of crystallizing in exactly similar or
very closely related crystalline form, i.e. they can exist in the same crystal
structure. Isomorphism takes place due to what is known as atomic
substitution i.e. replacement of one kind of atom by another of more; of less
similar atomic radius within the structure of the mineral concerned.
34
Potassium Feldspar, plagioclase feldspar, exhibit cleavage in two
directions at right angles.
C. Pyroxene Group
The pyroxene group of minerals forms another set of important rock
forming minerals. They occur in good abundance in dark colored igneous and
metamorphic rocks. In fact, among the ferromagnetism minerals, Pyroxenes
occupy first place as rock forming group.
Show single chain structure of silicates. one oxygen atom is shared
between two adjacent so4 tetrahedra.
The structure is typical chain structure of linked sio4 tetrahedral
(Inosilicates)
The pyroxene family minerals are generally dark in color. Their
hardness varies between 5 & 6 and specific gravity 3.2-3.5. Augite is an
important mineral of pyroxene family.
35
D. AMPHIBOLE GROUP
This group of minerals is regarded as a parallel to the pyroxene group
because most minerals of this group show a striking resemblance to the
pyroxene minerals in many of their properties. The fundamental difference is
the presence of hydroxyl (OH).
Color: Black or greenish black; streak, Colorless.
LustrE - Vitreous (like that of a broken glass).
Generally opaque.
Hardness 5 to 6; specific gravity 3 to 3.5 in amphiboles. The SiO4
tetrahedra are linked in double chain, it is for this reason that amphiboles are
more complex in this chemical constitution.
Fig. Horneblende is the most common variety of the Amphibole group
36
Horneblende occurs as a common mineral in acid and intermediate
igneous rocks such as Synites, Diorites Granodiorites and metamorphic
rocks.
E.Glivine Group – (neosilicate Group Fe - Mg Silicate)
A silicate mineral with magnesium and iron but no aluminum OIivines
are especially important in basic rocks and are thought to be a major
constituent of the oceanic crust and the earth's mantle.
Is a common rock forming mineral of basic, ultra basic and low silica
Igneous rocks (gabbaro, basalt, peridosite, dunite). It gets crystallized early
from magma, weathers readily at the earth's surface and gets
metamorphinsed to serpentine. (A greenish hydrous magnesium silicate
mineral).
Ultra basic rock - An igneous rock with silica content less than 44%.
This artificial boundary has now been abandoned.
•
Composition Iron-magnesium silicate. Rich in magnesium is known as
Fosterite Mg2sio4.
•
Rich in iron is known as fayalite Fe2sio4.
•
Clear varieties are used as gemstones.
•
Hardness 6.7; Sp gravity 3.2 to 4.3.
•
Crystallographic system: Ortho rhombic common form. Prismatic with
dome or pyramidal faces.
Fig: Orthographic projection
of a Crystal belonging to the
orthorhombic System.
Farm in ortho rhombic system
– prismatic with dome or
pyramidal faces.
37
F. Mica Group
Most important group of silicate mineral. Chemically this group is
different from pyroxene, amphibole and olivine groups. Mica group crystallize
in monoclinic system only are characterized with continuous sheet. Structure
Mica family (Si4o10)n-4
Average hardness 2.5; SG2.7 to 3.1
The important varieties of mica are:
•
Muscovite - White mica - Potash mica.
•
Biotite - Black mica - Mg-Fe mica.
•
Phlogopite - Brown mica - Mg-mica.
•
Lepidolite - Violet mica - Lithium mica.
Mica deposits occur in the form of books of varying thickness in the
oldest crystallize rocks known as Pegmatite. 3/4th of world production of mica
is obtained in India - Occur in Bihar and Nellore district Andhra Pradesh.
Being resistant to heat, it is used in furnace doors and as insulators in
electrical apparatus and machines.
It is also powdered, mixed with oil and used as a lubricant.
G. GARNET GROUP;
Alumina silicates of Ca, Mg, Fe and Mn.
Granites are silicates of various divalent and trivalent metals.
Divalent Ca2+, Mg2+
Trivalent Fe3+, Mn3+, AI3+, Cr3+.
•
Is a widely distributed mineral occurring most commonly in
metamorphic rock. There are several kinds of garnet of which the
most common one is red variety known as Almandine.
Vitreous, transparent to opaque.
38
Cleavage absent, cubic in form.
Hardness 7. S. G. 3.6 to 4.3.
Streak white.
Used as gem stone as well as abrasive:- occurs in all colors except
blue depending on their composition. Garnets crystallize in the cubic system
and occur as rhombdodecahedrns or Trapezohedron or as combination of
these two forms.
Fig: Garnet Dodecahedron (12 sides) Fig: An Isomeric crystal having
24 faces. The other common rock forming minerals are Epidote, Chlorite,
Limonite, Calcite, Magnetite, Hematite and ilmenite.
II. COMMON NON-SILICATE MINERALS:
The non-silicates that are most abundant at the earth's surface are
a) Carbonates - calcite, dolomite, magnasite.
b) Sulphates and chlorides - evaporites.
c) Iron-oxide minerals.
a. i) Calcite - common rock forming mineral in sedimentary rocks,
Secondary mineral formed from lime rich waters of sea\ and
oceans. The recrystallized variety of calcite makes the well known
metamorphic rock called marble.
ii) Dolamite - CaMg (Co3)2
Occurs as extensive layers of a stone rock called dolostone. Believed
to have been formed by the action of magnesium rich sea waters on
original limestone deposit. This process is called in petrology
Dolomitization.
iii. Magnasite MgCo3
Is formed from magnesium bearing waters of sea on their coming in
contact with other carbonate rocks. Large deposits of this mineral take the
39
form of rock bodies and become the source of commercial rock. Used as
refractory material.
EVAPORITES:
Are minerals that have bodies of water subjected to intense
evaporation. Example Common rock salt or halite Nacl.
Gypsum-CaSo4 2H2O.
The finely crystallized massive variety known as Alabaster is widely
used in carvings and sculpture, because of its uniform texture and softness.
Iron oxide minerals The chief iron oxide minerals that occurs abundantly at or near the
earth's surface are
Hematite (Fe2o3)
Limonite (Fe2O3, 2H2O)
Magnatite (Fe3O4).
40
SECTION B - SOIL SCIENCE
Introduction:
Soil is the most precious and vital natural resource of any nation. It is
the basis for all the living organisms everywhere at all times. Soil is
responsible to meet the requirement of peoples needs vig; food, fodder, fiber
fuel and fruits (5fs). It is therefore imperative that we should manage and
conserve the soil
Soil as a natural living body
•
The term 'soil' is derived from Latin word 'solum' the floor or
weathered portion of soil mass. Soil may be defined as a thin layer
of earth's crust which serves as natural medium for the growth of
plants. The soil is the natural body occupying the surface portion of
the earth composed of minerals and organic materials and having
more or less definitely developed horizons.
•
Soil is the product resulting from disintegration and decomposition
of rocks and also consists of decomposed remains of plants and
animals. Since soil is formed from the disintegration of parent rocks,
soil will resemble the parent rocks in its mineralogical composition,
but differ from the parent material in the morphological, physical,
chemical, and biological characteristics.
•
The soil is the weathered surface layers of the earth's crust which
has been altered by the influence of water, air, organic matters and
living organisms. Nature takes thousands of years to build up soils
and various factors of environment are responsible for their
formations.
Proximate constituents of the soil
o The soil is the heterogeneous complex system made up of solid,
liquid and gaseous materials. It contains four major ingredients:o 1. Mineral matters 50% - 60%.
o 2. Organic matter 5%
o 3. Water (soil solution! soil moisture 25% - 35%
o 4. Air 15%- 25% --- ----------------------- considered as a 3 phase
system; solid phase - mineral matters & organic matters, liquid
phase-soil water and gaseous phase-air.
41
•
The solid phase is in equilibrium with the liquid phase and gaseous
phase and the equilibrium is changing constantly on account of
variations in temperature and the moisture content of the soil.
•
And also due to removal of nutrients from the soil by the plants.
•
And due to the activities of microorganisms and other causes.
•
Mineral matter released from the minerals (p from apatite, calcium
from calcite, Mg from dolomite, k from mica, and clay from feldspar)
supplies plant nutrients to soil and then to plant in soluble form
through water contained in the soil.
•
Soil organic matters consists remains of plant residues, bacteria
and provides the soil N, soil P and sulphur.
•
For the formation of various chemical and biological changes in soil,
air is necessary.
•
For the transport of plant nutrients in soluble form from one part top
another part of the plant, water is necessary.
•
Phloem-vascular tissues that conducts synthesized food or sugar,
proteins and some minerals from top to bottom of the plant.
•
Xylem-vascular tissue that conducts water and minerals extracted
through roots to plant foliage for photosynthesis process.
Soil as Factor of Plant Environment
•
During rock decay many elements are released and they have a
specific bearing on soil formation and their subsequent release to
the soil for helping the crop growth.
•
Si & AI-furnish the skeleton for the production of clay colloids.
•
Fe & Mn --- carry out oxidation - reduction process and they
strongly influence soil colour.
•
K & Na --- are dispersing agents for clay and humus colloids.
•
Ca & Mg --- have high flocculating power and assure soil stability.
•
Within a given climatic region, the growth of vegetation is mainly
determined by the character of the parent material, whether
Iimestone, igneous rock sand deposit or clayey shale.
•
Water permeability of parent material in relation to soil formation:
The downward movement of the water is one of the prime factors in
42
the transformation of a parent material into a soil with characteristic
horizon differentiation.
o Hard and relatively pure limestone rocks frequently produce red
soil, whereas softer and impure varieties yield dark grey and
brownish weathering products.
Types of Soil Formed from Parent Rock
Rocks
Soil Formed
1. Granite & Gneisses
--
Acidic rocks giving rise to red soil and sandy
soil in general
2. Rocks containing Soda -feldspar (Na Al Si3O8)
Rocks hard weather slowly but provide
important nutrient and clay to soil, black soil
is formed
3. Cuddappah & Kurnool -formation
Black soil with high lime status
4. Dharwar system
red soil
5. Trichy
nodule
--
phosphatic --
not useful as soil but used as phosphatic
manure ores
6. Gondwana
--
not use as soil, represent coal bearing region
(coal – organic rock)
7. Deccan trap
--
black soil
8. Sandstone
--
Sandy red soil
9. Laterite
--
rich in sesquioxides (Al2o3 + Fl2o3)
10. Alluvial or Fluvial rock
--
alluvial soil
11. Hard
and
limestone rock
pure --
12. Soft
and
impure -limestone rocks
red soil
dark-grey and brownish weathering product
SOIL IN RELATION TO FORESTRY
Forest soil formation is governed mainly by the character of the
deposition of organic matter derived from the forest growth. The soils occur in
the hills district of Assam (They contain high proportion of organic matter and
nitrogen, in U.P in the sub-Himalayan tract and 'Coorg. (Karnataka)
•
They are peat soil containing more of organic matters. They are formed
by the leaching away of bases like Ca, Mg and K ions from the parent
43
material by heavy rains prevalent in that tract. As a result of leaching,
soluble silica is lost from the soil and sesquioxides accumulate. So
when water soluble phosphatic fertilizer is applied to this soil, they are
reverted to insoluble forms by the iron and alumina.
•
Forest soils are highly porous in nature, rich in organic matter content,
nitrogen and other nutrients. Texture varies from clay loam to sandy
clay loam. Acid solubles are low from 0.6 to 3%, pH is on the acidic
side from 3 to 4 due to low content of bases, nitrogen content ranges
from 0.1 to 0.75%
•
The most important living constituent of forest soil is the root system of
trees carrying beneficial mycorrhizal fungi which assist the trees in the
uptake of nutrients.
PRE-REQUISITES OF FOREST SOIL
A good forest soil should provide stability to the tree, space for suitable
spreading of the root system, moisture content in sufficient quantities at all the
times and nutrients to the required extent in a condition suitable for easy
absorption by the root system. The soil depth should be sufficient enough to
support the tree growth. The soil should neither be too firm nor too loose.
Loamy soils with crumby structure are the best for the tree growth. The
natural moisture requirement of the tree species should be available
throughout the growing season. This depends not only on the rainfall and
climate but also on the depth and texture of the soil.
Forests must usually depend for their nutrients on nutrient cycling (the
movement of nutrients from soil to plant to litter and to soil again) plus a small
amount (5-15 kg/ha/yearof N and K plus some sulphur) in precipitation and
some times appreciable amounts of nitrogen by bacterial fixation via under
story begumes. From one-fourth to two – thirds of N and K available (1/4 to
2/3) is recycled annually in litter. Suitable forests are fertilized once or twice
every 5 to 10 years because much of the added nutrients gets recycled for
several years. Leaf litter addition in forest varies as 1000 to 6000 kg/ha/year.
Rainwater composition
O2
= 30.7%
N2
= 61.8%
CO2
= 7.5
Total
= 100%
44
The forest soil differs from the agricultural soil in the following aspects:
Forest soil
Agriculture soil
Depth varies from few cm to various Depth is confined. Maximum is 1m.
metres
Sporadic spreading of roots.
Voluminous root system. roots have Little or no penetration power.
high penetrating power
Root system and rhizosphere soil
Root system carries beneficial contains microorganisms like fungi,
mycorrhizal fungi.
bacteria, actenomycetes etc.
Soil contains high amount of humus.
Poor content of humus,
The root secretions like amino acids, root secretions is little.
enzymes are great.
Highly porous, rich in organic matter
content, nitrogen and other nutrients. Pervious or impervious, poor in
organic matter content and nitrogen.
PH 2.0-4.0 due to presence of Fulvic
acid and humic acid. (Weak organic PH 6.0-8.0 due to the presence of
salts.
acids).
Forest soil is characterized by soils of
tundra, marshes, heaths, grassland Cultivated soil is bounded
and deserts.
boulders, stones, gravels etc.
by
Influences composition of tree stands,
rate of growth, wood quality, vigour,
Influences the growth of cultivated
stability against wind, degree of
crops.
resistance against diseases.
Pre-requisites are like depth, moisture
etc. are required in soil for a good
forest stand. Moisture should be
available throughout the growing
season.
Crops are raised according to the
existing
soil
conditions
and
modifications are made for a good
crop stand.
Moisture should be available upto
maturity stage.
Types of soils
The soil is the most important resource as it provides a medium for
plant growth. Soil is formed as a result of weathering of rocks in-situ and the
top layer of weathered particles consisting of sand, silt and clay in various
proportions gets, further modified by chemical and biological changes. The
45
types of soil is called in-situ soil or original soil, or residual soil or sedentary
soil. Soil may also be formed by the deposition of material transported by
agents of erosion such as river, glaciers, winds and waves. They are called
transported soils. The alluvial soils are the most wide spread among the
transported soils. The alluvial soils are the most wide spread among the
transported soils. Soils deposited by winds are common in deserts.
The ICAR has classified soils of India into 8 major types which are:
1. Alluvial soils
2. Black soils
3. Red soils
4. Laterite and lateritic soils
5. Forest and hill soils
6. Arid and desert soils
7. Saline and alkaline soils
8. peat and marshy soils
1. Alluvial Soils
•
Cover more than the 1/3rd of the total land surface and are the most
intensively cultivated areas. Found in the great northern plains from
Punjab to Assam valley, having been transported by rivers draining the
Himalayas and the peninsular plateau. Though alluvial soils are generally
fertile, they lack humus and nitrogen. Addition of nitrogenous fertilizers is
necessary for sustained yields.
Two types of Alluvial soils
1.
Khadar - never alluvium formed afresh by floods sandy, light
textured and less kankary in composition – low land plains –
high fertlie soil river alluvium.
2.
Bhangar – older alluvium coastal alluvium – upland plains
containing high clay – dark colour rich in kankar low fertile soil
acidic in nature.
2. Black soils
Occur in the Deccan lava region in Maharashtra, Gujrat, M.P. and
adjoining parts of Karnataka and Andhra Pradesh. Patches of black soils
occur in Tamilnadu, UP and Rajasthan. These contain high % age of clay and
hence retain soil moisture. Due to its moisture retentive nature, they are
suitable for dry-farming.
46
They are thinner and more dark colored on the uplands and hill slopes.
Dark colour of black soil is due to the presence of titaniferous magnetite.
3. Red Soils
Are well developed in granite and gneiss rocks of peninsula. Red color
is due to the content of the iron compounds.
Sandy or loamy in texture. Red soils are wide spread in Tamilnadu
uplands, Karnataka plateau, Andhra plateau and Maharashtra plateau outside
the deccan lava region. The central highlands from Aravalli mountains to
Chota Nagpur plateau have extensive areas of red soils. Red soils give high
yields under irrigation.
4. Laterite Soils
Soils are formed in the tropical areas with heavy rainfall and a marked
dry season. High rainfall results in leaching out of all soluble material from the
top layer of the soil. The soil contains nodules of hydrated oxides of Alumina
and iron. The surface soil forms a hard crust which is used for construction of
houses or as roads metal. These are generally infertile but respond well when
fertilizers are used. Occur widely in Sahyadris in Kerala, Karnataka am:!
Maharashtra and Eastern Ghats of Orissa and Andhra Pradesh. They occur in
hilly areas of West Bengal, Bihar, Assam and North-eastern states which
receive heavy rainfall.
5. Forest and Hill Soil
Occur on the slopes of mountains and hills in the Himalayas, the
sahyadris and the eastern ghats. These soils contain large quantities of
decomposed leaves, flowers and other organic matter called humus. At higher
elevations of Himalayas, the soils are podzols. At lower levels such as the
sahyadris and the Eastern Ghats, brown earths are common. These forest
soils are used for plantations of tea, coffee, spices and fruits. As these soils
are deficient in potash, phosphorous and lime, they need fertilizers for better
yields. The upper layers of soil are rich in silica and the lower layers are rich in
sesquioxides (Al2O3 + Fero3).
6. Arid and Desert Soils
These are predominantly sandy in texture and have salt content formed
by evaporation of sub soil moisture. These soils have low humus and
moisture content. These occur in the region west of Aravallis and north of
Kachch. Peninsula and south of Punjab and Haryana plains. They give high
yields when irrigated.
47
7. Saline and Alkaline Soils
In arid and semi-arid and arid tracts of Rajasthan, Punjab, Haryana,
U.P. and Bihar, soils have Na, Ca and Mg salt concentration on the surface.
These soils are infertile and are called Reh, kallar or usar soils. They occur in
areas of canal irrigation and in areas where water table is high. During the
long dry season, sub-soil water containing salts in solution is drawn upwards
by capillary action. Water evaporates leaving a deposit of salts. Alkaline soils
contain deposits of NaCI, Na2CO3, NaHCO3. Such soils can be reclaimed by
removing the salts and providing adequate drainage in the sub-soil.
8. Peaty and Marshy soils
These soils are formed under humid conditions and contain large
quantities of humus, organic matter and soluble salts. Such soils occur in the
western parts of Kottayam and Alapuzha districts of Kerala. Marshy soils
which contain a high percentage of humus occur in the coastal areas of West
Bengal. Orissa and Tamilnadu and in marshy terai region of Himalayas.
Distribution of total area Soil wise
Alluvial:
43%
Black:
13%
Red (sandy and loamy soils):
10%
Laterite and Desert soils:
16%
Mountain soils, Terai soils and Grey 9%
and Brown soils:
Other soils:
9%
Total
= 100%
The percentage distribution of major soil groups in India
Alluvial·
43.7%
Black and mixed Black and Red:
18.5%
Red, yellow and Laterite:
19%
Other :
18.8%
Total
= 100%
Red and yellow soils are generally poor. Laterite is also agriculturally
poor soil. Agriculture soil conditions vary greatly over the vast territory of India
and various steps are taken to reclaim the soils and maintain their fertility.
48
SOIL PROFILE
The properties of the soil are represented by the soil profile. A soil
profile is a vertical cross section of soil which represents a successive
horizons or layers of the soil from the surface down to the parent rock. Each
layer of the soil which can be distinguished from other by its color, structure,
texture etc. is called a soil horizon. It develops in nature by the disintegration
of rocks, giving the parent material which is acted upon by climate and
organisms, conditioned by topography for soil formation.
A soil horizon is a well defined layer within the soil profile, parallel to
the ground surface. Soil horizons are visually distinctive, reflecting their
different physical and chemical properties which results from various soil
forming process like weathering, addition of humus, movement of minerals
etc.
A soil profile is a historic record of all the soil forming processes which
take place in large periods of time and it forms the important unit of
Pedological investigations and in systematic soil survey. The character of the
soil profile is governed by climate as conditioned by topography and drainage.
The interaction of different factors of soil formation brings in a series of
physical, chemical and biological reactions. The combined effect if these
reactions are essential in the characteristics of the soil profile. Without profile
study soil classification is not possible.
Purpose of profile study.
A soil is characterized or classified by its profile or succession of
horizons. Profile study forms the basis for soil classification. A system of soil
classification determines the nature and characteristics inclusive of its
physical, chemical and biological properties and through this study, the value
of soil for agriculture as well as silvicultural uses can be determined.
Parent rock
Parent material
Physical + Chemical +
Biological reaction Geogenic
process confined to lithosphere
beyond the root zone (10-20
metres depth)
Soil
Classification
Soil profile soil
horizonz developed
over time
Soil forming factors
(cl, o, r, p, t)
Pedogenic process
confined to upper
Soil forming
surface of
process
hithorphere 1-2
metals depth
(like eluviation Soil
Illuviation leaching etc)
49
Soil forming processes mould the soil profile and its characteristics.
Different soil horizons are formed within the soil profile. The soil is classified
based on the different characteristics of the soil horizons. Profile study forms
the basis of soil classification.
The soil forming factors (Climate, organisms, topography, parent
material, time) act on parental material at lower depths and cause the
development of soil. The action of the soil forming factors is generally deep in
case of soft rocks and shallow in case of hard rocks. The soil forming
processes act on the soil and mould the soil profile with development of
sequence of soil horizons. In the vertical section of the soil body above the
parent material is called the soil solum and that including the parent material,
but not parent rock, if any, is the soil profile. The term soil development
commonly refers to the development of soil profile or pedon.
Under forestry soil conditions, the soil profile can be divided into five
main horizons (0, A, B, C and R). But it is not always true that all these
horizons are always present in each profile.
50
'C' = Regolith, the layers or mantle of loose, non cohesive or cohesive
rock material that rests on bed rock. 'C' is the mineral horizon or layer
excluding the bed rock. From regolith the solum is presumed to have formed,
relatively little affected by Pedogenic process. Regolith, a layer of crumbling
weathered material. As the rock is steadily broken down by the weather, a
layer of loose, weathered material called the regolith builds up on top of the
solid, unweathered rocks beneath. The lower layer; of rock is known as the
bed rock.
The 'O' horizon:
These are organic horizons formed above the surface of the mineral
matrix, mainly composed of fresh or partly decomposed organic matters. This
horizon is well developed in forests and may be completely absent in grass
lands, deserts and in open forest lands. This horizon is divided into following
two sub-layers.
1. 'O1' (AOO): This is the upper most layer consisting of freshly fallen
dead organic matter as dead leaves, branches, flowers and fruits, dead parts
of animals etc. These don't show evident breakdown.
2. 'O2' (AO): It is just below the ‘O1’ horizon in which decomposition of
organic matter has begun. Upper layers contain detritus in initial stage of
decomposition, in which material can be faintly recognized, whereas the lower
layers contain fairly decomposed matters called 'Duff'.
The 'A' horizon:
These are mineral horizons rich in organic matters and show
downward loss (eluviation) of soluble salts, iron or aluminum, CaCO3, Sio2,
humus, other salts also known as zone of Eluviation. This horizon is divided in
to two sub-layers.
(Eluviations is the mobilization and translocation of certain constituents
namely clay, Fe2O3, Al2O3, Sio2, humus, CaCo3, other salts etc. from one part
of soil body to other.)
1. 'A1' horizon: It is dark and rich in organic matters; organic matters
become mixed with mineral matters which are known as humus. This zone is
called a humid or: melamized region.
2. ‘A2' horizon: In this zone mineral particles of large size as sand or
more, with little amount of organic matter. This is also known as podzolic or
eluvial zone or zone of leaching.
51
The 'B' horizon:
The 'B' horizon is dark colored and coarse textured due to the
presence of silica rich clay organic compounds, hydrated oxides of
Aluminium, iron etc. Since the chemicals leached from 'A2' horizon become
collected in this horizon, it is also known as zone of illuviation or zone of
accumulation. This zone is poorly developed in dry area. 'A', 'A2' and 'B' are
collectively known as mineral soil or solum. (1Iluviation is the immobilization
and accumulation of the eluviated constituents at a depth beneath the soil
surface)
The ‘C’ horizon
These are the mineral horizon below the 'B', but excluding true bed
rock and without any characteristics of 'A' or 'B' horizons. It consists of large
mass of rocks incompletely weathered.
The R horizon:
This is the parent, un-weathered bed rock upon which water gets
collected is known as regolith
(Regolith is a layer of loose weathered material builds up on top of the
solid unweathered bedrock beneath)
Based on the stages of soil development, the soils are classified into 3
types.
1. Azonal soils are young soils
2. Interzonal soils are youth soils
3. Zonal soils are mature soils
Inert material, senile soils (Old age)
Azonal soils:
A young soil is one which is still in the process of adjustment to its
environment. Azonal soils are transported soils such as the alluvial soils of the
Great Plains and the coastal plains and sandy soils of deserts and colluvial
deposits. The characteristics are almost entirely those of the parent material.
These characteristics are lithological or inherited.
Zonal soils:
A mature soil is one which is in dynamic equilibrium with different
factors of soil formation with different factors of soil formation and profile
horizons are not appreciably changing either physically or chemically. A
mature soil reflects dynamic equilibrium with its environment. Time and
52
degree of maturity are factors used in many systems of soil classification. Its
distribution is related to climatic conditions. The red soils and lateritic soils are
zonal soils developed under tropical climate reflect the dominating influence of
climate and vegetation. Other examples are, Podzol, lateritic, Tundra, desert,
prairie, cherozem, chestnut.
Interazonal soils:
Soils which are developed according to peculiar local conditions of
rock, slope or drainage are called intrazonal soils.
Examples:
1) Hydromorphic soils of marshes, swamps (Estuary soils) flats and
seepage areas
2) Halomorphic soils: saline and alkaline soils, soils of imperfectly
drained arid regions, littoral deposits.
3) Calcimorphic soils: Brown forest soils. Brawnerde, Revdzina
soils
Profile, developed under vegetative cover (coniter forest area). It
consists of organic horizon O1 (A00) and O2 (A0). Below this, mineral matrix
with A1 and A2 horizons develop.
Profile developed under topography
Different soils may be developed at the top middle and bottom slopes,
though the parent materials may be the same. The soil differences are
brought by differential drainage differential climate, erosion, leaching etc.
In regions with high relief the water is lost rapidly and decomposition is
retarded and in turn it greatly speeds up the denudation process.
Endodynamorphism- soils whose properties are influenced by the
parent material i.e., original soil.
The characters of the soil are lithological or inherited.
Ectodynomorphism-Soils whose properties are mainly influenced by
factors other than parent material (transported soil).
Climate and Organisms are the active factors; relief parent material
and time are the passive factors.
Factors which tend to retard soil development are cold dry climate,
grass vegetation, impermeable consolidated parent material, and high in time
and steeply sloping topography.
53
SOIL FORMING PROCESSES
Soil forming processes mould the soil profile and its characteristics
Different soil horizons are formed within the soil profile. The soil is classified
based on different characteristics of soil horizons. Profile study forms the
basis of soil classification by which the value of soil for agricultural and
silvicultural uses can be determined.
Soil Genesis or Pedogenesis Process
Processes and factors involved in the formation of soil. The soil forming
processes which leads to the formation, transformation and rearrangement of
soil materials in a soil body leave their imprints in the different genetic soil
horizons which constitute soil morphology. Horizonation includes those
processes by which the soil materials are differentiated into several horizons
in a soil profile The soil horizons may be pronounced to be observed visually
or may have to be differentiated by means of certain soil characteristics.
Intermixing of soil horizon~ takes place in certain soils due to external factors.
This process of mixing in the soil body has been termed as ‘pedoturbation’.
SOIL FORMING PROCESSES
Fundamental processes
a) Addition of organic material matter to the soil.
b) Losses of the material from the soil
c) Transportation of material from the soil and deposition at other
1) Weathering- In situ decaying of rocks is the first step in the soil
formation. Weathering of rock produces the inorganic particles that give a soil
the main parts of its weight and volume. It is predominantey climate together
with biota which indicates the processes of weathering and soil formation.
Climate and biota (flora and fauna) constitute the active factors of soil
formation while passive factors are parent material, topography of the region
and period of time.
2) Translocation-It includes the various types of physical movements such as
a) Leaching-It involves downward movement of nutrients either in
solutions or in colloidal suspension predominantly occurring in humid areas. It
often results in the loss of nutrients from the soil body.
b) Eluviation - It refers to the washing down of finer clay particles and
minerals under the action of water. It leads to deprivation (disposes) of matter
from the A soil horizon.
54
c) Illuviation - It is accumulation of soil particles and minerals in the
lower layer. It leads to addition of matter in the B horizon.
d) Calcification-(Zonal group of soil)
Under condition of evaporation exceeding precipitation capillary action
leads to upward movement of calcium compounds bringing them in the upper
layers.
E>P
Occur in arid and semi arid region
This process involves the formation and deposition of CaCO3
and gypsum in one or more soil horizons.
It is common in the arid tropics with low rain fall. These types of soils
are rich in calcium with accumulation of CaCO3 and CaSO4 etc in the A
horizon.
The formation and accumulation of CaCO3 is called calcification and
CaSO4 is called gypsification.
Decalcification and degypsification takes place leading to the formation
of calcium horizon or Gypsic horizon down below.
Salinization/Alkalization (solonization)
A temporary accumulation of water in dry areas having high rate of
evaporation leads to the coming of the underground salts to the surface.
They occur in areas of canal irrigation and in areas where water table
is high. During the long dry season sub soil water containing salts in the
solution is drawn upwards by capillary action water evaporates leaving behind
a deposit of salts.
The saline soils (intra zonal) are formed due to accumulation of soluble
salts in soil horizon (CI and S04 of Ca, Mg, K and Na);these saline soil
become alkaline soils in the presence of plenty of water due to leaching away
of calcium ions. This results in de-flocculation or puddling of clay and
destruction of the normal structure of the, soil reducing it unfit for irrigation.
Alkalization (Solonization) is the process by which soils with high
exchangeable sodium and pH >8.5 are formed often sodium carbonate and
55
sodium bicarbonate are formed in extreme cases of alkalization. Such soils
are called Sodic soils or alkali soils.
De-alkalization (solodization) is effected by intensive leaching and
degradation which takes place in older soils. In this processes Exchangeable
sodium is replaced by hydrogen ions. There is simultaneous process of
argillation which results in the leaching of dispersed clay particles from the
upper to the lower horizons giving rise to a textural class.
Salinization is process of accumulation of soluble salts in the soil. The
intensity and depth of accumulation vary with the amount of water available
for leaching. Salinisation is quite common in arid and semi arid region.
Salinization may also take place through capillary rise of saline ground waters
and by inundation with sea water in marine and coastal soils. Salt
accumulation may also result from irrigation or seepage in areas of impeded
drainage.
Desalinization is effected by leaching of soluble salts from soil either
with rain water or with irrigation water of good quality
iii) Organic changes
Occurring mainly on surface and fallowing a sequential pattern, organic
changes involve breaks down of the organic materials by insects' worms. etc.
iv) Laterization / Desilication or Ferralization or Latosolization
This process involves in the chemical migration of silica out of the soil
solum and concentration of Fe and Al in solum with or without the formation of
Fe stones and concretions and decreas in the cation exchange capacity of the
soil.
56
These soils are developed under the hot and humid climatic conditions
of the tropical and subtropical regions of world. This process requires moist or
wet climate with moderate to high rainfall.
Silica is more mobile under hot and humid conditions. So they are
leached out in the Equatorial Rain Forest climate. Iron and Aluminum are left
out in the top layers. Horizon A becomes rich in red oxides of Iron and
Aluminum also called Ferralsols. Because of the presence Of Hydroxyl ions
and Aluminum ions, these soils are highly acidic. Leaching is very much
pronounced here.
V) Melanization or Humification
Is a process by which dark colors are imparted to the soil due to the
decomposition of organic matters.
During the process of Melanization the humus from the organic layers
infiltrated by pecolating water or broken up by the activities of organisms, is
incorporated in to the mineral soil horizon.
Melanization results in the development of mull or muck, a type of
humus mixed with soil having high nutritive value, Because of the
incorporation of organic matter melanised soil exhibits high cation exchange
capacity. It improves nutrient contents and enhances stability of the soil
fertility factors.
Further decay of
(Mineralization) in to the soil.
Degradation
humus
release
Humification
nitrogenous
compounds
Mineralization
Taken up by plants
Plants and
Animals
vi) Gleization:Is the process of reduction, due to anaerobic conditions, of Iron in
waterlogged soils with the formation of nodules and concentration of Iron and
Manganese.
Ferric oxide is reduced to a soluble Ferrous Oxide under waterlogged
and anaerobic conditions by some specialized bacteria. This leaves behind a
57
bluish grey Gley horizon. On the soils some times appear blotchy (dark spots)
typified by patchy red colour.
vii) Silication / Podzalization / Cheluviation
This process occurs in cool humid climates having conifer forests,
when the conifer leaves disintegrate and decompose; they emit certain acids
because of the chelating agents present in the soil.
Is the process in which Iron and Aluminium form certain sesquioxides
which are soluble in water and leached out. The upper horizon becomes rich
in Silica and the lower horizon rich in sesquioxides. Sometimes, the i1luvial
zone of Iron and Aluminium leads to the formation of Iron pan which is
impermeable.
This is the process of eluviations of oxides of Fe and AI and also of
humus under Acid conditions (pH 4.5), removal of carbonates by organic
acids formed by organic matter, and illuviation of the sesquioxides and humus
in subsurface horizons. Abundant organic matter commonly found under
forest, cool climate and abundant moisture under humid climatic conditions
are favourable for such processes. The eluviated horizon assumes a
bleached grey appearance and is left in a highly acid, siliceous condition.
Because of grey color and ashy appearance, the term “Podzol” has been
used for such soils.
This condition occurs in cool temperate regions with
fairly high rainfall. The leaching water depletes the "A"
horizon of its sesquioxides (Fe and AI), clay and organic
matters. As a consequence, clay, Fe and AI accumulate in
"B" horizon. The colloidal complex of the A horizon
becomes more or less saturated with H+ and it is rendered
extremely acidic.
58
Si 4-
Fe3++ Al3+
Major Soil Groups
Soil classification:As with plants, animals and rocks, soils also need to be defined and
arranged into suitable categories such as Orders, Suborders, Groups,
Classes, and Types etc. No two soils even an inch apart are identical in all
respects. A soil is characterized or classified by its profile or succession of
horizons.
The system of classification based on the features of their profiles was
first introduced in 1879 by the great Russian Pedologist Do-Kuchaev.
According to his concept, the soil is classified based on its genesis I. e. the
historical features of soil profile formation.
Based on the maturity and stages of soil development, the soils are
classified into three types:Soil classification by Thorp and Smith (1949):
1) Zonal soils (mature):The zonal soils have well developed characteristics that reflect the
dominating influence of climate and vegetation. A zonal soil is one which is in
dynamic equilibrium with different factors of soil formation, and the profile
horizons are not appreciably changing either physically or chemically, e. g.
Podzol, Laterite, Red soil, Tundra, Desert, Prairies (grasslands) Chernozem,
and Chestnut soils.
Chestnut and Chernozem
These soils have been subjected to calcification under grass
vegetation. This accounts for the high organic matter content noticeably
present in the Chernozem and deep in the horizon.
But the zone of CaCo3 accumulation is found near the surface in the
Chestnut than in the Chernozem.
Due to scanty precipitation Chestnut soils are much lower in organic
matter than Chernozem and the layer of carbonates is near to the surface.
The surface soils are neutral or even Alkaline. Gypsum is likely to be present
in the sub soil.
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2) Intrazonal soils (youth soils):The profile horizons have to undergo some changes for complete or full
development of soil with distinct horizontal variations. Soils which are
developed according to peculiar local conditions of rocks, slope or drainage
are called lntrazonal soils. E. g.
Halomorphic soils:-saline and alkaline soils.
Hydromorphic soils: - marshes, swamps (estuary soils), flats and
seepage areas.
Calcimorphic soils:-brown forest soils, Rendzina soils
Rendzina soils:- Rendzina, calcareous regur black soil rendoll or dern
Carbonate soil. A grey brown or black soil developed from soft lime rocks of
medium texture developed above parent materiel with a high calcium
carbonate content such as limestone. This soil type is unsuited for agricultural
use.
Terrarosa: - residual red clay mantling a surface or limestone left by
streams which sink at sink holes, composed of limestone, left formed under
humid conditions.
3) Azonal soils (young soils):These soils lack distinct profile characteristics. They are still in the
process of adjustment to its environment. In the early stage of soil formation,
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the characters are entirely those of the parent material. These characteristics
are Lithological or inherited.
These are the soils without any well developed soil profiles, because of
their recent formation and extreme immaturity or steep relief or very sandy
parent material. Most azonal soils are developed on recent alluvial or colluvial
deposits.
e.g. Alluvial soils, Lithosols, Regosols (dry sand). (Lithosol a group of
shallow soils lacking welt defined horizons and composed of imperfectly
weathered fragments of rock).
This type of soil is still in the process of adjustment to the current
situation viz. Change of climate, cultivation, clearance of vegetation, lowering
of ground water, removal of salts. As a result of readjustments, there may be
some modifications in the nature and appearance of horizons.
Vilenski’s modern genetical classification of soil
1) Thermogenic
2) Phytogenic
3) Hydrogenic
4) Halogenic
1.Thermogenic : Soils with characteristics due to difference in temperature
and rainfall. Polar, termperate, Humid, Arid, semi arid, tropical, sub tropical,
high rainfall, low rainfall. E.g. Podzol soil, (temperate and cool climate).
Laterite soil (high rainfall and high temperature)
Limy soil (calcareous) - arid tropics with low rainfall
2. Phytogenic: Soils with characteristics due to difference in vegetation.
E.g. grassland soil/pasture soil, forest soil (dense vegetation), and
desert soil- xerophytes.
3. Hydrogenic: soils with characteristics due to an excess of moiture
E.g. Swamp or estuary soil (the mouth of the river valley where fresh
water intermixes with sea water as it has a free connection with open sea but
within which the salinity level of the ocean is considerably diluted by the
addition of fresh water brought in by a river system).
Glacial or moraine soils, marine soils, alluvial soils, lacustrine soils
(deposited in lakes).
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4. Halogenic: Soils with characteristics due to an excess of soluble salts
present now or at some previous time during their form.
e.g. Saline soil (CI, SO4 of Ca +Mg)
Alkaline soils (Na2CO3, NaHCO3, and NaCI)
Marlout's (USAD) (1928) classification of soil based on the occurrence
of carbonates and oxides. :
a) Pedo-cals: (soils rich in CaCO3)
(Incompletely leached)
b) Pedalfers: (Soils rich in R2O3 or sesquioxides)
(AI2O3+Fe2O3)
(Completely leached)
SOIL TAXONOMY
It is scientific grouping of similar soils.
A basic system of soil classification for making & interpreting soil
surveys. Soil Taxonomy (meaning, arrangement of soils).
It is a classification of soils according to natural relationship among the
soil characteristics. A soil is a product of parent material having been changed
over time by climate & living organisms & modified by relief.
Yet taxonomy relates to these natural soil forming factors & processes
only as they have imparted observable & measurable charcteristics to the soil.
Taxonomy is concerned with classifying & arranging such natural individual
soil characteristics as horizons, soil moisture regimes, soil temp. regimes, soil
texture, soil mineralogy, soil structure and soil colours.
To classify individual soils, some minimum soil volume must be chosen
that will represent an individual soil. Such a minimum volume called a Pedon
is about 1msq. (40 in sq.) & as deep as roots grow. Pedon is a unit of soil
taxonomy- the basis for differentiating soil map units when mapping soils.
USDA Soil Survey Staff (1975) has published a comprehensive system
of soil classification called 'The Seventh Approximation'. In the Seventh
Approximation, 6 categories of classification are defined.
Classification level in decreasing orderI Order ............10
II Suborder ..........47
III Great soil group ........180
IV Sub group .......960
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V Family ..........4700
VI Soil series ........10,500
I Order is the highest category of soil classification. This is a broad
division of soils due to similarity in the profile characteristics formed by the
dominating influence of climate & vegetation. All world soils are placed into 10
orders.
USDA's system of classification is based on the factors that can be
inferred & observed from the field i.e. Observed soil properties rather than
genetic considerations. There are 10 orders, 47 sub orders, 180 great groups,
960 sub groups, 4700 families, & 10,500 series. The 10 orders of soils in the
new scheme are as follows:
1 Entisols
2 Vertisols
3 Inceptisols
4 Aridisols
5 Mollisols
6 Spodosols
7 Alfisols
8 Ultisols
9 Oxisols
10 Histosols
1. ENTISOLS (Alluvial soils, recent soils, transported soils)
-Weekly developed, alluvial deposits, transported . soils- no distinct horizons
in the profile. Sometimes referred to as 'embryonic mineral soils.' The zonal
scheme equivalent of these soils is the ‘Azonal soils’.
2. Vertisols cracking clayey soils, usually dry soils - horizontal variations not
apparent -usually black cotton soils.-are formed only in the tropical and sub
tropical latitudes. Top soil will be inverted e.g. Deccan region soil. During
summer cracks develop and in rains cracks are closed - Disturbed and
inverted clay soils. The zonal equivalent of these soils is Grumusols.
3. INCEPTISOLS:
-moderately developed soils.
-occurring in humid climate. -profile developing soil. - have clay content in B
horizon. Lack intense weathering and leaching e.g. Flood plains of Ganga,
Brahamputra, Mississippi, Amazon, Congo.
Horizon development has been retarded because of cold climate, water
logged soils or lack of time for stronger development.
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4. ARIDISOLS:
Are soils of dry areas, semi desert and desert areas of mid latitudes (3060degree N) - soils with minimm organic matter content- has high base status
and lack of leaching - no water retentive capacity - have no available water.
have ephemeral grasses (shortened grasses) and scattered xerophyte plants
such as cacti - occurs in hot deserts of Rajasthan and adjoining belts of
Gujarat, Haryana and Punjab - The zonal equivalent of Aridisols is the
Sierozem
5. MOLLISOLS:
Soils with high base status and with a dark "A' horizon.
Soils with organic matter and mineral matter. Crumb structure associated with
praire vegetation
-grasslands soils rich in organic matter and high in bases are called mollisols.
Occurs in temperate grasslands, in forests of U.P., Himachal Pradesh and
Northeastern Himalayas
The upper horizon is rich in divalent cations and the lower one is clayey.
The zonal equivalents of Mollisols are the Chernozems, chest nut and praire.
6. SPODOSOLS:
Are leached soils of cool coniferous forests.
-soils with accumulated organic matter plus iron and aluminium oxides.
Are generally acidic with an ashy A horizon. Are the cold and tundra region
soils.
The zonal equivalent is Podzol.
7. ALFISOLS
These develop in humid and sub humid climates.
Soils with argillic horizon and moderate to high base content. They are the
developed soils. They have a horizon of clay accumulation in the sub surface
horizon the zonal equivalent is ‘Degraded chernozem’. Some of the red and
laterite soils of India have been classified as Alfsols. They are slightly to
moderately acid.
8. ULTISOLS:
Ultisols are strongly acidic, extensively weathered soils of tropical and subtropical climates.
-Soils with argillic horizon and low base content
-Occurs in parts of Assam and north eastern Himalayan region.
9. OXISOLS (Old soils - senile soils)
-Highly weathered tropical and sub- tropical soils are called oxisols.
-High Fe content laterite soil
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-Low, fertility status.
Laterite- concentration of Fe and AI in the A horizon thereby removing silica
(desilication).
Lateritic- contains sesquioxide rich zone high.-Fe content
The sesquioxode rich material associated with high Fe content (lateritic soil) is
new termed as Plinthite.
10. HISTOLS:
-Soils developed in organic material
-Most histosols are peats or mucks consisting of more or less decomposed
plant remains that accumulated in water
-Soils in water logged areas with high organic matter are called histosols
-Undecomposed organic matter content soils
11. ANDOSOL - A dark coloured fine grained silica rich volcanoic soil
12. REGOSOL – Composed of dry and loose dune sands or loess.
Classification of the major oil groups of the world or world pattern of
soils
A. Zonal Soils
1. Pod zols (ash-soil)
2. Brown earth
- These are found under milder climate supporting a deciduous
forest cover. Humus is well distributed throughout the soil profile and is less
acidic than in Podzol. Free Ca2+ is absent from the upper part of the profile.
There is no downward movement of sesquioxides and their dispersed
distribution gives rise to the overall brown colour of the soil.
3. Tundra soil
- In areas of active slope movement, soils are invariably thin where
there is no plant growth.
- the soils are ahumic – a treeless region confined mostly to latitudes
beyond 600N of the equator and south of the polar ice. Vegetation is
characterized by mosses, lichens, sedges and rushes interspersed with
grasses and flowering herbs. Towards the southern margin of the Tundra, low
woody plants and deciduous dwarf shrubs such as older, birch and willow can
be found.
The tundra is found under both humid and arid condition and the soils
which develop are of little agricultural value.
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4. Chernozem soils
5. Chestnut soils
6. Praririe soils
7. Sierozems
8. Grumusols – are dark clayey soils of savannah or grass covered areas
which have a warm climate with wet and dry season. There are no eluvial or
illuvial horizons but the shole solum is rich in bases especially calcium and
hence its dark colour. These soils are characterized by a high degree of dry
season craking. This is some what similar to black soil.
9. Ferralsols
B. Intrazonal types
1. Hydromorphic soils
2. Calcimorphic soils
3. Halomorphic soils
c. Azonal types
1. Alluvial soils – Immature soils
2. Regosols – are composed of dry loose dune sands or loess
3. Lithosol – are accumulation of imperfectly weathered rock fragments
on steep slopes where erosion rates remove soils almost as fast as it is
formed.
- a group of shallow soils lacking well defined horizons and
composed of imperfectly weathered fragments of rock.
Soil survey and soil mapping
Soil survey is the study and mapping of soils in the field under their natural
environment to,
1. Determine the important characteristics of soils
2. Classify the soils into defined classification units
3. Establish and delineate boundaries of different kinds of soils on base map
4. Correlate and predict the adaptability of soils to various crops, grasses and
trees, their behavior and productivity under different management systems
and the yields of adapted crops under defined sets of management practices
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Modern soil survey are carried out for two purposes
1. Fundamental; Study of various types of soil present in a locality or a region
for the sake of knowledge and classification
2. Utilisation; The knowledge thus obtained is made use for maximum crop
production
Depending upon the objectives and intended use of the map three types of
soil surveys are recognized.
1. Detailed soil survey or large scale survey
Village cadastral maps or large scale base maps of scale 16" = 1 mile
or 8"=1mile is to be used. Two to three profile pits for every 600acres are to
be examined (1 profile for every 120 ha).
where the soil units SST - dx
Sy-e2
which is the mapping unit to be demarcated. Where SST is soil
type, dx = depth class, Sy = slope class e2 = erosion class The boundary of
the mapping unit is determined by detailed transverse of the field taking auger
boings or stated intervals and recording the details thus observed on the map
Detailed soil survey is a comprehensive map and glves the kind and
amount and geographical distribution of individual soil. It gives various
information which are needed for planning land use and management at the
community level and for planning agricultural research and extension
programmes. The large scale soil surveys are made for intensive land use
planning that requires detailed information about soil resources for making
prediction of the suitability and treatment needs. The information can be made
use in planning for general agriculture, construction, urban development and
similar uses that require precise knowledge of the soils and their variability.
2. Rapid reconnaissance (small scale survey)
Toposheets of the survey of India are used as base maps of scale 1" =
1 mile or 1 cm = 0.5 km is to be used i.e. small scale base maps are used.
The field traverse is made at wide intervals hence less time consuming than
detailed survey. Profile pits as 4-6 km traverse are to be examined
Rapid reconnaissance soil surveys are carried out only when new and
relatively undeveloped vast areas are taken up for improvement. It permits
rapid survey of large areas where development cannot wait the completion of
detailed soil survey. On the other hand the maps and reports prepared out of
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this survey are less precise and cannot be utilised for planning of individual
farms or for detailed soil conservation methods.
Rapid reconnaissance soil survey provides initial information about
large area from which potential areas for detailed survey could be selected.
This gives a broad understanding of soil and is useful in new and less
developed areas for general planning as in mountain regions. The small scale
soil survey are made to collect information on soils of very large areas at a
level suitable for planning regional land use and interpreting information at a
higher level of generalization. The primary use of this information is selection
of areas for more intensive study.
3. Reconnaissance (medium scale survey)
The medium scale surveys are made for extensive land uses that don't
require precise information of small areas. The information can be used in
planning for range, forests, recreation use and similar extensive land uses
and in community planning. Soil map and survey report of a place based on
soil survey is useful for rational land use planning, soil conservation, forest
management, land reclamation etc. On the basis of soil survey maps and
repots land capability classification has been developed in which every acre of
land is classified according to its capability and limitation.
Utility of soil survey and soil mapping
Soil survey followed by soil mapping and soil classification provide
information that one may need for a specific purpose
1. It shows the distribution of different soils on maps in an area
2. It defines their adaptability for crops, grasses, trees, their management
requirements and yields of individual crops under different system of use and
management.
In addition to the above soil surveys for specific purpose can also be
taken up
1. Fertility soil survey
To asses whether the soils in the region are adequately supplied with
N, P and K for growing satisfactory crops.
2. Irrigation Soil survey
To find out the suitability of soil before and after irrigation. Irrigation
project brings forth a lot of new problems such as accumulation of soluble
salts, alkali formation and soil deterioration.
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3. Reclamation soil survey
To diagnose the problematic soils like acid, calcareous, alkali and salini
soils and specific treatments for their reclamation.
4. Soil conservation survey
To assess soil erosion, slope class and erodibility of soils of the area
depending upon the degree of slopes and erosion, suitable engineering
agronomy soil and forestry devices will be adopted. It provides information as
to manage the watershed effectively based on the capability of lands for use.
Rock – Soil plant relationships
Soil may be defined as thin layer of earths crust which serves as
natural medium for the growth of plants.
Soils are formed as a result of weathering of rocks and minerals.
Weathering is the disintegration and decomposition of rocks and minerals by
physical and chemical processes. The former involves mainly physical
breaking down into smaller particles where as the latter is responsible for
chemical decomposition leading in course of time to the formation of new
products. The first stage of weathering is the formation of the parent material
which is subsequently subjected to a series of soil forming process as formed
at a place of parent material; the soils are called as sedentary soils. The black
soils of India formed on basaltic rocks and parent material in the peninsular
region are examples of sedentary soils.
Before the process of soil formation starts; the parent material may be
transported through the action of water, ice, wind, gravity and deposited at
some other place, where the prevailing soil forming agencies operate and
produce soil. Depending upon the agency of transport, the soils are called
alluvial, marine, lacustrine, glacial, Aeolian (by wind) and colluvial (by gravity).
More than one transport agency may be operative but the naming is done
according to the dominating agency.
Coupled with weathering, climate (precipitation and temperature),
organism (flora and fauna) and relief (elevation and slope) act slowly over
time on parent material to form the soil. Given sufficiently long period of time
(20-50 years), the soil forming factors act on parent material at lower depths
and cause development of soil profile which represents a succession of soil
horizons down to and including the upper part of the undifferentiated parent
material. The action of the soil forming factors is generally deep in the case of
soft rocks and shallow in case of hard rocks. As and when a sufficiently thick
mantle of soil material is formed over the rock surface weathering process is
69
slowed down but the dynamic reactions continue to take place in the soil
body. Soil is thus in effect a dynamic system.
The process of weathering and soil formation combined to determine
the size distribution of particles of soils which consists of primary and
secondary minerals. Rocks and minerals are basically composed of iron and
aluminum silicates. Gradually the soil body becomes the habitat of variety of
biological materials viz, plants, animals and microorganisms. Eventually the
dead and transformed tissues of this material form the organic component of
the soil. The organic components in combination with the mineral particles
together form the soil body. Living organisms contribute to the biological
activity of the soil. Thus the soil is not a dead body but is the seat of
tremendous activity of billions and billions of soil organisms. These organisms
play a major role in supporting plant life.
Thus some soils are red, some are black, some are deep some,
shallow, some are coarse textured and some are fine textured .They serve as
a reservoir of nutrients and water for crops, provide, mechanical anchorage
favourable tilth. The components of soil are mineral materials organic matters
water and air the proportion of which vary andwhich together form a system
for plant growth.
Soil forming materials
Soils parent material are derived from three kinds of rocks :
1. Igneous rocks
2. Sedimentary rocks
3. Metamorphic rocks
The igneous rocks are formed by cooling, hardening and crystallizing
various kinds of lava and differ widely in their chemical composition .They
chiefly contain feldspar, minerals andquartz. Rocks having high portion of
quartz (65-75%) are classified as acidic ,where as those containing < 50% of
quartz as basic .The common igneous rock found in India are granite (acidic)
and basalt or deccan trap (basic).
The sedimentary rocks formed by deposition of fragments of igneous
rocks, contain shale, conglomerate, sandstone andIime stone .Alluvial, glacial
and oeolian deposits form the unconsolidated sedimentary rocks.
The metamorphic rocks are formed from the igneous and sedimentary
rocks by the action of intensive heat and high pressure or both resulting in the
considerable change in the texture and mineral composition .The common
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metamorphic rocks are gneiss from granite, quartzite from quartz or
sandstone, marble from lime stone and slate from shale.
PHYSICAL PROPERTIES OF SOIL
Soil is a heterogeneous mixture of silicate particles humus and a variety of
insoluble
salts andoxides of metals called the solid phase, liquid phase and a gaseous
phase.
Mineral matter 50-60%
Organic matter 5%
Soil moisture 25-35%
Soil air 15-25%
Two important physical properties of soil are soil structure and soil
texture.
Soil texture is concerned with the size of the mineral particles .It refers
to the relative % of distribution of sand, silt and clay i.e., various size groups in
the soil.
Soil structure refers to the arrangement of soil particles Le., sand, silt
and clay into defined pattern like columnar, prismatic, platy etc
Texture is the permanent character where as structure will be easily
changed by management practices .Texture shows the weathering stage to a
certain extent .where as structure is not. Texture is influenced by the
presence of soil separates and organic matter.
INTERNATIONAL CLASSIFICATION OF SOIL PARTICLES
Coarse textured
Diameter
1. Gravel
> 2mm
2. Coarse sand
2 – 0.2 mm
3., Fine sand
0.2 – 0.02 mm
Fine textured
4. Silt
0.02 - .002 mm
5. Clay
< 0.002 mm
The various groups of soil particles are known as soil separates. Soil
texture is estimated in a laboratory by mechanical analysis, where as in the
field by Feel's method.
In the mechanical analysis of soil ,soil particles larger than sand >2mm
are separated by sieving .The sand silt and clay percentage are then
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determined by the methods which depend upon the rate of settling of these
separates from suspension. Robinson pipette is the apparatus commonly
used form determining particle sizes by sedimentation.
PRINCIPLE OF MECHANICAL ANALYSIS
A freely falling particle is known to acquire acceleration due to gravity
.But if it is allowed to fall in a medium as in a soil suspension, which can offer
resistance to the motion of falling particle by virtue of medium's viscosity,., the
falling particle will experience a drag and very slowly, it acquires a velocity
with which it falls in the medium .This velocity is called the terminal or
sedimentation velocity.
Viscosity: It is the resistance to flow offered by liquid.
According to Stoke's law the viscous force of the medium is given by
6πrηv which balances the gravitational force, of the falling particle is given by
4/3πr3(db-df)g
acting on single particle of radius v-(equivalent spherical radius).
6πrηv = 4/3πr3(db-df)g
v = 2/9 (db-df) gr2
η
Where as V is the sedimentation velocity (cm .sec-1)
dP = density of particle (gm cm -3)
df = density of fluid (gm cm - 3)
n = viscosity of suspending fluid (gm sec.cm-1).
g = acceleration due to gravity (cm .sec -2).
v = equivalent spherical radius of particles (cm).
This relation ship is known as Stoke's law propounded by G.G.Stoke in
1850.
Stoke suggested a relationship between the radius of spherical particle
and the rate of its sedimentation in a liquid .He stated that the resistance
offered by the liquid to fall of the particles varied with the radius of the sphere
and not with the surface
In case of systems where dp, df, η and g are constants at specified
temperature, the above is simplified to
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V = k r2 (the density, gravity and viscosity are expressed by a constant k).
Thus the sedimentation velocity is directly proportional to the square of
the radius of particle ‘r’ i.e. V α r2
According to the proportion of soil separates present, soils are
classified ~ into different soil types
1. Coarsed textured -sandy soil-light textured soil
2. Medium textured –silty soils Le, loam andsilt loam
3. Fine textured -clay loam, heavy soil or energy soils or clayey soil.
Coarse textured soils are generally low fertile and water holding
capacity when
compared to fine textured soils .Such soils are well aerated and drainage is
effective. They don't hold more water readily ,but they yield a good amount of
stored water in sub soils.
Clayey soils or fine textured soils retain more water and causes water
logging but contain more Nitrogen and exchangeable bases than coarse
textured soil. Thus the texture influences plant growth by controlling water and
nutrient availability.
Soil structure
Soil structure refers to the arrangement of soil particles ie., sand, silt
and clay into defined pattern like columnar, prismatic, platy etc. The primary
particles of soil viz, sand silt; clay don't occur singly but are often ; aggregated
or bound together by organic substance and iron oxide ,carbonates, clay and
silica .Other chemical compounds may also act as binding agents in the soil.
Each natural aggregate is called a ped -a unit of soil structure formed
by natural process. Naturally formed aggregates are called peds where as
artificially formed mass is called ‘clod'.
The quantity of soil structure is expressed by pore space while the
quality of soil is expressed as fine, very fine, medium, coarse and very
coarse, If the primary particles are not aggregated they are described as
structureless and may be single grained.
The air and water relationship of a soil depends on its structure .So soil
structure has been regarded as the key to soil fertility.
Texture is the permanent character and cannot be changed over
periods of time where as structure will be easily changed by management
practices .Texture shows the weathering stage to a certain extent ;Where--as
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structure is not .Texture is influenced by the presence of soil separates and
organic matter. The best structure favourable for soils is crumby or granular
structure is maintained by management practice like ploughing ,draining, or
liming the acid soil, fertilizinq or manuring But the addition of organic matter
and growing of legumes build up and maintains Structure.
Grasses improve the soil structure better than the legumes since the
constant cycle of growth and decay of fine rootlets is very intimately
distributed through the soil.
Structure is determined by estimating pore space. If it is above 50%,
the structure is good.
Pore space % = (1- bulk density/particle density) x 100
(space occupied by air and water)
Soil pores of various shapes and sizes may be filled with either water
or air or by both. Bulk density or apparent density or apparent specific gravity
is defined as the mass of a unit volume of dry soil.
B.D = weight of a known volume of air dry soil(including pore space)
Weight of an equal volume of water
Particle density or true density or absolute specific gravity of mineral
soil particles is described or defined as the mass of a unit volume of soil. It is
expressed as gm/cm3.
P.D = M
V
Particle density
=
Mass of oven dry soil
Volume of oven dry soil
(Excluding air and water)
Particle. density is assumed to be the same for most soils (Le. 2.65
gm/cm3). A bulk density determination is all that is required for the calculation
of total pore space.
EFFECT OF LIME ON SOIL STRUCTURE OR RECLAMATION OF ACID
SOIL
In acid soil clay particle are closely associated and this interferes with
air and movement of water and therefore granulation is highly desirable. A
satisfactory crumb structure is somewhat encouraged in an acid soil by the
addition/of any form of lime, although the influence is largely indirect.
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Lime application greatly enhances the decomposition of soil organic
matter and synthesis of humus. This effect encourages granulation which is
the desirable character for plant growth (loam texture crumb structure or
granular structure is good for crop growth).
Acid soils are made more suitable for agricultural use by liming which
raises the soil pH.
Liming of acid soil is practiced for obtaining granular structure which
will improve (the crop growth. The reactions that take place by lime
application may be expressed as follows:
CaCO3 + H20 + C02 Ca (HCO3)2
Ca(HCO3)2 Ca2+ + 2HCO3H soil + Ca2+ Ca soil + 2H+
(acid soil)
H+ + HCO-3 H2CO3
H2O + CO2 The higher the soil moisture, the more rapid rate of reaction. Ca2+ ions
replace the exchangeable H+ ions.
Liming material is to be applied to raise the soil pH which indirectly
indicates beneficial soil structure.
Other liming materials:
1. Dolomitic limestone Ca Mg (CO3)2
2. Industrial waste rich in CaO viz. basic slag, cement factory waste, paper
mill sludge
3. Rock phosphate serves as a source of phosphate in acid soil.
Legumes are responsive to lime application .• lime + NPK application
increases the yield of wheat, maize, jowar and jute. Calcicolous plants or
trees which love calcium grow well. Dry type teak grows on lime rich soils.
Calcicole (of plants) . growing best on calcareous soils.
Bombax ceiba
Tectona grandis
Terminalia paniculata
Pterocarpus marsupium
Dendrocalamus strictus
Abizzia amara
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Cupressus torulosa
(Calcifuge : (of plant) growing best on acid soils (pH 2.0 – 4.0)
Calcifugous plants :
Abies pindrow (silver fir- tall evergreen tree)
Juniperus communis
Juniperus macropoda
Rhododendron arboreum
SOIL COLOUR
Colour of soil is mainly due to two constituents;
1. Organic matter
2. Weathered minerals
Soil colour expressed by three variables viz., Hue, Value and Chroma
The soil color is determined by Munsell colour chart.
In the Munsell colour chart, three basic hues are considered viz Red
(R), yellow red (YR) and yellow (Y) 5 YR is hue 5/6 where 5 is value and 6 is
chroma. 5YR is called Hue. The dominant spectral color or rainbow colour
(red, yellow, blue and green)
(VIBGYOR) on scale of 0-10
5 value - the amount of reflected light (relative light or black) on scale 0-10.
6 chroma - relative purity, strength or saturation of colours on scale 0-20.
Black colour indicates organic and peat soils.
White or grayish color indicates poor in organic matter.
The soil color directly influences the soil temperature.
The dark colored soils absorb more heat e.g. black soil.
SOIL AIR
Soil air is the gaseous phase within the pore space of the soil. About 50% of
total volume of soil is pore space which is occupied by air and water. As the
pore space of the soil is partly filled with water and partly by air, the amount of
air varies with the amount of water. When the soil is in good condition for crop
growth, air content makes about 20- 25% by volume.
76
Constituents of soil air
The constituents of soil air are oxygen, nitrogen and carbon dioxide.
Oxygen is essential for the respiration of plant roots and for the activity of
beneficial microorganisms. It influences the absorption of nutrients by plant
roots. Nitrogen of the soil air is made use of by the nitrogen fixing bacteria
both symbiotic and non- symbiotic.
Carbon Dioxide of soil air influences the availability of mineral nutrients by
solvent action.
Sl.no.
Soil air
Atmospheric air
1. Nitrogen
79.2
79.0
(% by volume)
(high)
2. Oxygen
20.6
20.97
(low)
3. Carbon dioxide
0.2
0.03
(high)
Organic matter addition and cropping increases the level of carbon
dioxide in soil. Thus soil air contains a higher proportion of carbon dioxide
under tropical condition than under temperate conditions.
Soil aeration refers to the processes whereby air in the soil is
exchanged with air from the atmosphere. The gaseous exchange is a natural
process.
MOVEMENT OF SOIL AIR OR GASEOUS INTERCHANGE
The interchange of gases between the soil air and the atmospheric air
is brought about by two mechanisms.
1. Mass flow: - due to total gas pressure difference between atmospheric air
and soil air.
2. Diffusion: - due to partial pressure difference or concentration gradient
between soil air and atmospheric air. In mass flow the entire mass of air
stream moves from a zone of high pressure to low pressure and is relatively
unimportant in determining the total exchange that occurs.
Diffusion: - it takes place under the concentration gradient.
The amount of diffusion gas is proportional to the concentration
gradient.
Ficks Law if diffusion
q = - D. dc/dx
dc/dx is concentration gradient
77
q = the amount of diffusion gas in unit time across a plane of unit area
D =diffusion coefficient
q is equal to D when dc/dx concentration gradient (the change in
concentration in unit distance) is unity (1).Since the gradient is in the direction
of lower concentration dc/dx is negative. The inter space voids between
aggregates are
paths of diffusion. The pores larger than 15 microns(15 x 10-3 mm) which
control drainage water contribute to the diffusion process.
SOIL WATER / SOIL MOISTURE
Under tropical conditions, soil moisture is present mainly in liquid form.
Soil water is the 'Life blood of soil'. Without water, plant growth becomes
standstill. Evaporation, infiltration, drainage of water, diffusion of gases,
conduction of heat and movement of salts and nutrients are all dependent
upon the amount of water present in soil.
Briggs (1897) suggested that soil water from dryness to saturation may
be classified under four heads viz,
1; chemically combined water
2. hygroscopic water
3. capillary water
4. gravitational water
Forms of soil water:
Gravitational water
1. Chemically combined water
Certain compounds like Limonite (2Fe2O3.3H2O) in soil held the water
in chemical combination called combined water or Water of hydration. Since
this water is chemically combined, it does not moisten the soil at all and is
usally ignored.
78
2. Hygroscopic water(Unavailable water)
When an oven dry soil is exposed to the atmosphere, it absorbs water until
equilibrium is established between the water in the soil and the water vapour
in the atmosphere, the amount depending on the temperature, humidity, soil
texture etc.
The water thus absorbed is known as hygroscopic water.
Figure :
Gravitational water
Water of
adhesion
Field capacity
Water of cohesion
Soil
Zone of progressive
thickness
Hygroscopic water
Capillary water
Water of crystallization
or chemically combined
water
The percentage of moisture taken up by a dry soil, when placed in contact
with an atmosphere saturated with water vapour (100% humidity at any
particular temperature, is known as the hygroscopic coefficient of the soil at
that temperature and is expressed on the dry soil basis. Hygroscopic water is
the water adhered to the soil particles and held with great force ranging from
31 to 10000 atmospheres. The smaller the size of the particles, the higher the
percentage of hygroscopic moisture. This water is held to the surface of soil
particles with such high suction force that plant roots are unable to extract it.
Hence it is wholly unavailable for biological activities of the soil.
3. Capillary water(available water)
The moisture is held in the pore spaces between the soil particles. This is the
capillary water and held by different sized pores in excess of the hygroscopic
coefficient and is held by surface tension against the force of gravity. It is held
at the tension below 31 atmospheres of the hygroscopic coefficient and less
than 1/3 atmospheres of the gravitational water. This capillary water is
important for plant growth. Capillary water movement is ineffective soils when
the water table is below 80 cm.
79
4. Gravitational water (Free water or drainage water or superfluous water)
- is defined as the water which is not held by the soil but drains under the pull
by gravity. It is held with a water potential less than 1/3 atmospheres (<1/3
bar) and is also called as Free water as it can move freely downward under
the force of gravity. It is unavailable to plant because it usually drains rapidly
and is lost: Also designated as superfluous. The movement of Gravitational
water downwards through the soil is called Percolation. This water is removed
from the soil.
At 1/3 bar suction, the water content in the draining zone will
subsequently change only slowly and the soil is said to be at field capacity.
The water content of soil at 1/3 bar suction has been taken to represent field
capacity.
If the gravitational water is allowed to remain in soil, it excludes air and
interferes with respiration and normal biological activities in soil. It is therefore
essential that the superfluous gravitational water is removed. Otherwise,
water logging condition result.
Field capacity:
Field capacity is the percentage of soil moisture that is held with water
potential of 1/3 atm. and is a measure of the greatest amount of water that a
soil hold ort store water under conditions of complete wetting followed by free
drainage.
Field capacity approximates the amount of available water in a soil
after it has been fully wetted and all gravitational water has drained away
usually in a day or two.
Plant available water is equal to the difference of water percentage at
field capacity and at permanent wilting point.
Plant available water = Water at field capacity (1/3atm) -Permanent
wilting point (15atm) .
Wilting point moisture:
Wilting point is the percentage of water in a soil at which plants will wilt
for lack of moisture and having wilted will not recover when water is again
added. It is also called the permanent wilting point Wilting coefficient and
critical moisture point.
The water content at 15 bar suction is the permanent wilting point
(PWP) which is defined as the water content of soil expressed as percent of
80
oven dry soil at which plants wilt and do not recover turgidity even when water
is again added.
Plants can only use capillary water held by not more than 15 atms
(point of permanent wilting).
Force acting on soil water include matric potential, gravitational
potential and osmotic potential..
Water held in the soil at a given potential remains in that state until a
suction exceeding that is applied. As water gets released first from larger
pores and subsequently from progressively smaller pores. Release of
successive increments of soil water require increasingly higher amounts of
suction.
The portion of water released from soil in the suction range of 1/3 bar
and 15 bars referred to as Field capacity and permanent wilting point
respectively, is conveniently assumed to be plant available water.
Energy relations of water in soil
Energy associated with soil water may be kinetic and potential. Kinetic
energy (KE = ½ mv2) is usually considered negligible as water movement in
soils is quite slow.
Potential energy (PE = mgh) often referred to as potential is the one
which determines the state and movement of water in soils.
The potential of free water is taken as zero.
81
Plants can only use capillary water held by not more than 15 atm (the
point o~ permanent wilting). Soil water at the air dry state is held by water
potentials that vary from 1000 to 300 atms depending on humidity.
Movement of water in a saturated soil
•
-depends upon the permeability of soil. In a saturated soil, pores
of all sizes are filled with water. The quantity flow of water in a
saturated soil is quantified by Darcy's law.
Darcy’s law (1856) states that the velocity of flow of water through a
column of saturated soil is directly proportional to the difference in the
pressure head and is inversely proportional to the length of the soil column.
qα∆H/L
Where ‘q’ is the velocity of flow in cm/sec.
H = difference in pressure head in cm
L = Length of the soil column in cm
q = K∆H/L
Where 'K' is the proportionality factor and is termed as Hydraulic
conductivity ‘∆H/L' is the Hydraulic gradient
i.e. the difference in hydraulic head per unit column of length
Hydraulic conductivity (K) refers to the readiness with which a soil
conducts or
transmits fluids through it.
Movement of water in unsaturated soil
Soil pores are partly filled with water and partly with air.
Water in unsaturated soil exhibits very little tendency to move.
Movement is very slow and mainly by adjustment of the thickness of water
films on soil particles. In unsaturated soil, the size of the pores in which water
moves varies. According to Poiseuilli's law, the rate of flow of water will vary
with the fourth power of radius of the tube or pipe.
q αr4
where q = velocity of flow in cm/sec.
r =radius of soil pipe in cm.
Hence, a reduction in radius by one half results in a sixteen folds reduction in
flow rate.
82
e.g. [1/2]4= 1/16
r=(2)4=16
If the radius increases by 2 times results in sixteen fold increase in flow
rate.
Conductivity in unsaturated soil is very much affected by the size and
the relative abundance of different sized pores. As water moves from a
position of high energy to low energy, the water will move progressively from
the larger pores first.
Expression of soil moisture tension (capillary potential) -the PF value.
Water is held by the soil with a certain amount of tenacity or pull. The
force which is required to abstract (remove) water from the soil at any point is
called the capillary potential at that point.
The tenacity of soil for water is called the soil moisture tension and is
due to the forces of adhesion and cohesion. Water retention in soil with force
is measured in PF units. The tension with which the water is held within the
soil particles are expressed in terms of energy either as atmosphere or
pressure or bar or PF value. The standard atmospheric pressure / average air
pressure at sea level is 42 kg/sq.cm.
The energy values are expressed as the logarithm of the tension in cm
of a column of water. This value is called PF similar to the pH of H+ ion
concentration. SCHOEFIELD introduces the PF scale where P = logarithm
value,
F = force or free energy.
PF is defined as the logarithm of the height of the column of water in
cm. equivalent to suction force with which water is held in equilibrium with a
soil at a given moisture content. Thus the tension or force equivalent to a
height of column of 10cm of water corresponds to PF = 1, of 100cm to PF =2 of
1000cm to PF = 3 and so on.
The relationship between PF, height of water and atmosphere is given below.
PF- value
0
1
2
3
4
5
Height of water in cm
1
10
100
1000
10000
100000
Atmospheric pressure(appro)
1/1000
1/100
1/10
1
10
100
83
6
7
2.54
4.2
4.5
1000900
10000000
346
15849
31623
1000
10000
1/3 field capacity
15 wilting point
31 hygroscopic co-efficient
CHEMICAL PROPERTIES OF SOIL
1. Nutrient elements
From the atmosphere and the soil, the plants take the raw materials
like CO2, O2, N, H2O and minerals for the manufacture of plant food through
photosynthesis using energy from the sun. Sixteen elements (C, H, O, N, P,
K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo, B and CI) are needs for the growth of a
plant.
N, P, K - macro nutrient elements.
Ca, Mg and S- secondary elements and rest are micronutrients.
Macronutrients
Nitrogen is an important constituent of amino acids, proteins, enzymes and
some non-protein compounds also. If N availability is less, plant growth is
affected Chlorosis develops in plants. It encourages above ground vegetative
growth of plants and imparts dark green color to plant.
Phosphorus is a constituent of sugar phosphates and phosphotides
viz. ATP and ADP. Energy transformation and metabolic process in plants are
tided by phosphorus besides stimulating the root growth.
Potassium essential for plants, retain water and withstand temporary
droughtiness and impart resistance power to enable plants to resist fungal
and 'bacterial diseases. It is essential for tuber crop.
Secondary nutrients
Calcium is helpful in grain and seed production.,
Magnesium is a component of chlorophyll and chromosomes directly
involved in photosynthesis.
Sulphur is required for the synthesis of amino acids and proteins.
Increases oil content in oil bearing plants.
Micronutrients
These are required in small quantities for the plants and microorganisms.
They all function as catalyst or are atleast closely linked with some catalytic
processes in plants.
84
Considering the role played by various essential elements they may be
grouped as under :
Group 1: Energy exchangers - Hydrogen and oxygen
Group 2: Energy storers - C, N and P
Group 3: Translocation regulators - Na, K, and Ca and Mg.
Group 4: Oxidation - Reduction regulators - Fe, Mn, Mo, Cu, B, Zn and
Chlorine
2. Soil pH (Soil reaction)
Soil reaction expressed in terms of pH is one of the most enlightening
characteristics
known to exercise significant influence on many soil
properties, chief of which are
1. Nutrient availability
2. Biological activity
3. Soil Physical conditions
The term pH (from French Pouvoir, hydrogerne i.e. hydrogen power) was
proposed by Sorensen to indicate either acidity or alkalinity, it is defined as
the negative logarithm of the hydrogen ion concentration in gram atom per
liter (moles) per liter.
pH = - log 10 (H+) or log 10 [1/H+]
The hydrogen ion concentration is generally expressed in terms of the
numerical
value of the negative power to which 10 must be raised in order to express
the required concentration and is denoted by symbol pH.
pH scale 0 - 14
0-6 acidic
7 neutral
8 – 14 alkaline
Acidic solution (H+) = 10-010-1 10-2 10-3 10-4 10-5 10-6
pH
=0
1
2
3
4
5
6
H + = 10 -7, pH =7 (neutral)
Alkaline solution (H+) = 10-8 10-9 10-10 10-11 10-12 10-13 10-14
pH
=
8
9 10
11
85
12
13
14
Soil acidity is caused by ionisable hydrogen atoms or protons while soil
alkalinity is caused when the activity of hydroxyl ions in the soil solution phase
is more than that of the hydrogen ions.
Sodic soils or alkaline soil has a sodium adsorption ratio of the
saturation extract of 13 or more and electrical conductivity of the saturation
extract is less than 0.4 siemens/metre. The pH of these soils usually ranges
between 8.5 and 10. These soils are found in arid and semi-arid regions in
small irregular areas called ‘Slick spots’. The pH of calcareous soils is usually
above 7.0 and may be as high as 8.3.
Nutrients
N
P
K
Ca, Mg, S
Mo
Al, Fe, Mn, B, Cu, Zn
Available range
6–8
6.5 – 7.5
5.5 – 7.5
5.5 – 6.5
>5
<5
Soil reaction and plant growth are inter – related as a result of the
significant effect of soil reactions on soil environment. High pH generally
lowers the availability of all nutrient elements except molybdenum and boron
i.e. pH<5.
Sodic soil has a sodium adsorption ratio of the saturation extract of 13
or more but has low salt content. Formally, these were called black alkali.
The SAR is defined as
SAR = Na+/√Ca2+ + Mg2+ / 2
The exchangeable sodium percentage (ESP) of a soil is
the
percentage of exchangeable sodium ion to the total soil exchangeable cations
of all types in the soil sample.
ESP = Exchangeable sodium ion
x 100 = > 15%
Soil cation exchange capacity
Electrical conductivity of saturation extract is less than 0.4 siemens
/metre and sodium adsorption ratio more than 1:3. The pH of these soils
usually ranges between 8.5 and 10. These soils are the Hilgard's black alkali
and Russian ‘Solonetz’ soils. These soils are found in arid and semi- arid
regions in small irregular areas called 'slick spots'. The pH of calcareous soil
is >8.5.
86
3. Silica sesquioxides ratio :
The proportion of silica to sesquioxides (iron and AI oxides) in the clay
fraction of the soil expressed as molar ratio and also is called the Silica
sesquioxide ratio.
Molar ratio = SiO2
or ____SiO2___
R2O3
Al2O3 + Fe2O3
The molecular ratio of silica to sesquioxides (R2O3= AI2O3+Fe2O3) of
soils and
their clay fraction has been taken as a measure of the degree of weathering.
ln humid tropical climate, there is considerable loss of silica with consequent
enrichment of sesquioxides. In heavy soils of the semi-arid regions (e.g. black
soil contain high proportion of clay) the silica content is high.
The value may be about 6.0 in the original and range from 1.25 to 3.6
in most soils.
Laterite soils < 1.33
Red soils
= 2.5-3.0
Black soil
= 3.0-4.3
The silica sesquioxide ratio is one of the single value constants that
gives a clue to the properties of the soil. The ratio is high in a clay soil and low
in coarse light soil. A high ratio goes with high Base Exchange hygroscopic
and field moisture capacities and fertility in general. Thus the silica
sesquioxide ratio is indicative of many of the physical and chemical properties
of soils.
High ratio indicates montmorillonite (2:1 crystal lattice)
SiO2
Al2O3
SiO2
SiO2
Al2O3
SiO2
87
Low ratio indicates Kaolinite (1:1 crystal lattice)
SiO2
Al2O3
SiO2
Al2O3
Soil organic matter
The diagnostic feature of soil is the presence of organic matter and
microorganisms. The highest organic matter content i.e.> 15% are obtained
for grassland in humid temperature regions and in peat soils and the lowest
values in arid tropics (<0.5%).
Decomposition of organic matter in soil
Plant residues + farmyard manure in soil decomposed by microorganisms
H2O+CO2+NO3--+SO4-- + Humus + Other products
Higher the temperature higher the organic mater decomposition in the
soil. optimum moisture content favours microbial activity which favours
decomposition.
The inorganic form of nitrogen is converted into organic forms which
are not assimilable by higher plants. This process of conversion of inorganic
nitroger into complex organic substances of nitrogenous form is known as
nitrogen immobilization
The immobilized nitrogen in dead bodies of the
organism is again converted by microbes into inorganic forms, ammonium or
nitrate which can be utilized by plants and microorganism this process is
known as nitrogen mineralization.
Mineralization and immobilization constitute a continuous process in
soil and is in dynamic equilibrium and support plant life on the earth's surface.
This process is not necessarily restricted to nitrogen alone
Mineralization
= immobilization
immobilization
availability of plant nutrients to plants
Mineralization
88
Mineralization or mobilization
Organic residues, humus, protein } aminization RNH2
Amino acids
Ammonification
NO3 -
Nitrification
NH4+
Immobilization or fixation - converse of mineralization
NH4+
and
NO3 -
Biological
Proteins, nucleic acids
Activities
and organic complexes
Activities
The principle store house for large amounts of the nutrient anions is
soil organic matter. The organic matter also holds more than 95% of the soil
nitrogen from 58-60% of the total soil phosphorus and as much as 80 % of the
Sulphur. Each
of these elements is specific in its function in plant metabolism.
Organic matter in soil is a dynamic material; it changes continuously as
a result of microbial activity. It can therefore be maintained at a reasonably
stable level both in quality and quantity by means of suitable addition of new
organic materials like addition of crop residues and green manuring and
growing leguminous crop in a crop rotation, The decomposition of organic
matter is vigorous in coarse sandy soil where aeration is maximum. In clayey
soils decomposition is less rapid due to less aeration. This is the main reason
for the low organic matter content in sandy soils than in heavy soils.
C: N ratio of organic matter and its significance
The carbon -nitrogen ratio is meant the ratio of carbon to nitrogen in
the soil organic matter. There is a relationship between organic matter and ~
nitrogen content of soil. Since carbon makes up a large and rather definite
proportion of this organic matter, the C/N ratio of soil is fairly constant
If the added organic matter contains limited amount of nitrogen, the
micro-organisms utilizes it in their metabolic processes. When materials of
varying C/N ratios are incorporated into the soil, the resulting humus in the
soil has the same C/N ratio of 10 to 12: 1
89
C to N ratio in humus is 12: 1· However, much this ratio may be
distributed it always tends to reach this value.
If the ratio of C to N in plant tissue is wide (low N content 80: 1), the
micro organisms have plenty of C for synthesis and for energy but there may
not be enough N for synthesis. Decomposition is slow, N remains locked up
as complex microbial proteins and is not available to crop. So the crop starves
for nitrogen The crop leaves exhibit signs of hunger for nitrogen. This can be
overcome either by supplying extra nitrogen or by growing a legume and
incorporating in the soil.
Nitrogen present in the organic matter becomes converted into
ammonia and nitrate and available to crops only if the C/N ratio is 25: 1 or
less.
When the C: N ratio is lower than 12: 1 (i.e. N in excess), the total N in
excess of the ratio is immediately converted into ammonia and nitrate by
microorganisms. The nitrate so formed may be utilized by the crop or may be
lost from the soil in the drainage water.
C: N ratio of the soil or the added organic material may be sufficiently
narrow to prevent excessive bacterial fixation of the soluble N compounds.
C:N ratio in the soil can be altered to some extent by the application of N
fertilizer by growing legumes. Soil nitrogen
Nitrogen- source
: Atmosphere is the main source (79% N) reaches the soil by
•
Symbiotic N fixation taking place between rhizobium and
leguminous plants.
•
By non symbiotic N fixation taking place by free living bacteria
viz Azatobacter (aerobic) and clostridium (anaerobic) species.
Nitrogen in soils in organic form
1. α-amino form 24-37%
2. Nucleic acids 3-10%
3. Amino sugar 5-10%
Nitrogen losses from soil
1. Liquid leaching
2. Gaseous losses
i. Denitrification
90
ii. Ammonia volatilization
3. Erosion
4. Crop removal
Nitrogen balance in soil
Native available N
Losses
+
Crop uptake
+
+
Added N
Removal by crop.
Nitrogen cycle nature
The never exhausting nature of N in the atmosphere and this source is
tapped by nature to supply nitrogenous food to the plant kingdom. Animals in
turn, depend on the nitrogenous plants for their energy and life processes.
Nitrogen cycle in nature is also called Biological Nitrogen Fixation. In
the nitrogen cycle, bacterial play an important role in the different stages of
the cycle.
Nitrogen compounds and ammonia formed from atmospheric nitrogen
are added to the soil by rain water.
By the activities of symbiotic and symbiotic bacteria, ntirgen from the
atmosphere is absorbed and added to the soil through leguminous and non
leguminous plants.
Proteins, synthesized by plants are used by animals. The excreta of
animals and the dead remains of animals and dead tissues of plants and cells
of micro – organisms are added to the soil.
Due to dentirfication process free N is liberated and gets into the
atmosphere Nitrates formed in the soil are leached by drainage. In spite of
nitrogen loss through leaching and volatilization. N status of soil is improved
by nitrogen cycle.
91
Atmospheric
nitrogen
Nitrogen fixation by bacteria
Electrical
discharges in air,
rain, water
Symbiotic in plants
(Rhizobium)
Denitrification
by p.bacillus
Non symbiotic in
soil (Azotobacter
clostridium)
Also by
industrial
fixation and
lightning
Birkland and
Eyde’s Arc
process and
Haber’s
process of
synthesis of
Ammonia
Dead organic wastes
In soil (Humus)
Death & Decay
Proteins
Plant organic N
Animal Organic
Animal organic N
Proteolysis
(Protein Fragmentaiton)
Nitrification by
Nitrobacter,
Nitrifying Bacteria
Nitrite ‘N’
(NO2-N)
Immobilization
Nitrate “N” (NO3-N)
Denitrification and
immobilization
Cells in M. Org.
Amino acids
(building blocks of proteins)
Ammonification Mineralization
Nitrification by
Nitrosomonas
Nitrosifying Bacteria
Fig. Nitrogen cycle in nature
92
Ammonia
SOIL COLLOID
Thomas Graham (1861) divided the soluble substances into two classes
depending on their power to diffuse through vegetable or animal membranes.
1. Crystalloids and
2. Colloids.
Crystalline substances such as sugar, salt and urea which in solution
diffuse rapidly through animal or vegetable membranes were known as
crystalloids.
The other class of substances like gelatin, starch, glue etc. which are
found in an amorphous state and which exhibited little or no tendency in
solution to diffuse through animal or vegetable membranes were called
colloids.
Excepting the purest sea shore sand all soils contain particles of
colloidal, size. These are divided into two groups.
1. Inorganic or mineral colloid or Clay colloid.
2. Organic or Humus colloid.
Clay, organic colloid and silica posses negative charges where as
sesquioxides bear a positive charge. But due to the prominence of clay and
organic colloids, they give the soil a negative charge.
Clay in association with small quantity of organic matter is called Soil colloid.
The humus is often referred to as an organic colloid and this gives stability to
soil structure. It has a cation exchange capacity, many times greater than that
of clay colloids.
Cation exchange is an important reaction in soil property (Le. exchange of
one positive ion by ,another positive ion is called cation exchange). This
reaction is used in correcting soil acidity and basicity; in changes altering soil
physical properties. Cation exchange takes place on the surfaces of clay and
humus colloids as well as on the surface of plant roots. The proportion of
these cations on the colloid surfaces are constantly changing as ions are
added from dissolving minerals or by the additions of lime, gypsum or
fertilizers.
93
SOIL BIOLOGY - BIOLOGICAL PROPERTIES
The soil is seeming with life comprising of organisms which are visible
to the naked eye and micro organisms or microbes which can be seen only
with the help of a microscope. The different forms of soil organisms cooperate
and compete and they interact with each other to form an integrated system
which functions in a major way to affect the break down of organic material. In
this way, the recycling of plant nutrients is promoted.
The study of microbes in soil is called Soil Microbiology which is considered
as a branch of soil science.
The soil organisms are classified into two broad groups viz. Soil flora
and Soil Fauna which are again subdivided depending on their size into:
1. Soil macro flora
2. Soil micro flora
3. Soil macro fauna - which are larger than 1 cm in size.
E.g. Earth worms.
4. Soil micro fauna - the size ranges from 20-200µ
94
Important groups in each class are shown in the following figure.
SOIL ORGANISMS
Soil fauna
Soil flora
Soil Microfolroa
Soil Macroflora
(Roots of higher
plants)
Soil Macroflauna
Earth worms
Moles, ants
Frogs and Toads,
Snakes and Lizards,
Rodents (>1 cm in
size)
Mesofauna
200 µ - 1 cm
Soil mites
(Acaina)
Spring tails
(Collembola)
Bacteria
Fungi
Moulds
Actionmycetes
Yeast
Mushroom
Algae
Blue green algae
Grass green alage
Yellow green algae
Golden brown
algae (datoms)
Cellulose decomposer
Protein decomposer
Lignin decomposer
Humus former
Heterotrophic
Symbiotic N fixer
Non symbiotic N fixer
Ammonifier
Cellulose decomposer
Autotrophic
Nitrite former (Nitrosomonas)
Nitrate formers (Nitrobacter)
Denitrifier
Slphur oxidiser
Iron oxidiser
Hydrogen oxidiser
95
Soil Microfauna
Protozoa
Nematodes
(20-200µ)
CLASSIFICATION OF MICROORGANISMS
Microorganisms are classified on the basis of morphology ,shape, and
size temperature sensitivity, requirement of molecular oxygen ,sources from
which they derive carbon for body building and energy for the vital processes
in the body and also special biochemical transformation they carry out. Based
on the ability to grow in the presence or absence of molecular oxygen
,microbes are of two categories :
Those which need molecular oxygen are aerobes and those which
grow only in the absence of molecular oxygen are anaerobes but become
inactive in the presence of oxygen. Those which generally grow and adapt in
the presence of oxygen but can also adapt themselves to grow under an
oxygen depleted environment are termed as FACULTATIVE ANAROBES
The microorganisms grow and develop within a certain range of
temperature. Those which grow below' 10 degree Celsius are known as
PSYCHROPHILES. Those which grow between 20-400C are Mesophiles and
those which ,find temperatures higher than 45 C suitable for their proliferation
are thermoptliles. The organism which thrive well in an acidic medium are
Acidophilic and those which thrive well in an alkali medium are Alkaliphilic.
The last two terms are not very commonly used.
Based on the energy and carbon requirement for cell synthesis, soil
microorganisms are divided into two broadgroups-viz hetrotrophs and
autotrophs.
Autotrophs the organisms which can manufacture of its own organic
substances from inorganic materials .They utilizes carbon from carbon dioxide
for cellular synthesis. Most chlorophyll containing plants are autotrophs
carrying out photosynthesis process.
Hetrotrophs depend ultimately on the synthetic activities of the
autotrophic organism. They require a supply of organic material (food) from
which to make most of their own organic substances. e.g all animals,
fungi,bacteria.
The autotrophs are further subdivided into chemoautotrops which
derive~ their energy from oxidation of simple inorganic compound~ and
photoautotroph which derive their energy from sunlight.
Beneficial role of soil organism
The most important role that microorganisms carry out and have significant
bearing on soil properties and plant growth are
96
1) Decomposition of organic matter
2) Synthesis of humic substances in soil
3) Biologlcal fixation of atmospheric nitrogen
4) Microbial transformation of nutrients and
5) Nutrient cycling in soil
97
PART B – LAND USES & WATERSHED MANAGEMENT
SECTION C - HYDROLOGY
It is the science which deals with the occurrence, distribution and
disposal of water on the planet, earth. It also deals with the behaviour of water
on the surface of the earth and below the surface i.e. underground. Hydrology
pertains to precipitation and the surface runoff.
The globe has 1/3 land 2/3 rds oceans, 2/3 rds of the earth surface is in
the form of oceans, rivers, lakes, snow, glaciers and ground water. Of the
amount of water available 97% is in oceans 2% is locked up in glaciers and
ice caps. 1% is locked up and is available as fresh water i.e. in lakes, ponds,
rivers, tanks, ground water, aquifers and this 1% fresh water is available for
use vi., industries, livestock, urban and rural water supplies and agriculture.
In India water consumption is
Industry power generation ...........................................1.50%
Livestock
........................................... 1.40%
Municipal and rural water supplies .............................. 3.73%
Agriculture ....................................................................-93.27%
Total............................................................................... 100%
HYDROLOGICAL CYCLE
Hydrological cycle is the water transfer cycle which occurs continuously
in nature. From the beginning of the time water has: been constantly and
continuously in motion .Little has been added or lost over the years.
HYDROGICAL CYCLE: relates to constant circulation of water in nature
between the earth and atmosphere water is essential for life processes of
man animal and plants. Without water life cannot be maintained .Water is
received on the planet earth through precipitation or rains. When rains fall on
land, it is received on the surface of the soil. When the intensity of rainfall
exceeds the rate of entry of water in the soil the excess flows away as surface
runoff. The surface runoff depends on
1. intensity of rainfall
2. infiltration capacity
3. percolation 'and permeability
4. slope ,
5. vegetal/vegetative cover
98
It is necessary to understand how the water received from rain on the
plant earth is spent.
IMPORTANCE OF HYDROLOGICAL CYCLE
Water budget
The amount of rainfall received in area through hydrological cycle and
the amount of utilizable of water in that area depends on
1. precipitation
2. evaporation and transpiration
3. infiltration
4. surface runoff
Water balance illustrates how the precipitated rain is spent in different
ways on the surface of earth, i.e, during a given period. The total inflow into a
given area must be equal to the total out flow from the area plus the change in
storage.
This is explained by means of hydrological equation which reflects the law of
conservation of matter which states that matter can neither be created nor
destroyed but can be converted from one form to another
I = O ± ∆S
Where I =Inflow
O =outflow
∆S =change in storage
This is still more refined and expressed in the form of water Balance Equation.
This water Balance can be explained by means of an equation. The concept
of water balance helps to identify water surplus areas and water deficit areas.
Only in water surplus areas water can be harvested from the runoff and used
for drinking, agriculture and hydel power generation.
P = E + R → I ↓ ± ∆S
(the arrows up and down indicates the direction of water movement)
Where
P = Precipitation
E = Evaporation from the soil surface from water surface and
from plant surface
99
R = Surface runoff
I = Infiltration into the soil
∆S = Change in storage
i.e change in soil moisture content in the basin over the time ∆t
Water balance explains the different ways of receiving water on the earth and
different way’s of utilizing water on the surface or in the basin. The water
balance of a basin or a sub basin states that in a specified period of time all
the water entering a basin must be consumed, stored or go out as surface or
sub surface flow.
The interrelationship between inflows, outflows and accumulation is
expressed by water budget Equation.
Water Budget Equation
∆S
= Σt∆t - ΣQ ∆t
Where Σt∆t = Represent All forms of recharge (Infiltration + Penetration)
over a time ∆t
ΣQ
∆t = Represent net discharge from the basin including seepage,
pumping surface flow( surface runoff) and evapotranspiration over a time ∆t
∆S = Change in the ground water storage in the basin over a time ∆t
The intensity and duration of rainfall would affect the erosion and
runoff. When the intensity of rainfall exceeds the infiltration rate, the excess
flows out as surface runoff thereby causing soil erosion this aspect is adopted
or followed in all watershed areas. For the efficient management of watershed
it depends on the total precipitation and subsequently surface runnoff.
The precipitation is not uniform in its distribution, frequency and
intensity due to climate differences. A knowledge of precipitation is required
for estimating runoff, planning erosion control measures, removing and storing
excess water and in conserving water in low rainfall region.
Knowledge of runoff is required for designing structures and channels
that will manage and guide the natural flows of water. Data about infiltration,
evaporation and transpiration are required for planning moisture conservation
practices and in designing irrigation and drainage systems .
Of all the forms of infiltration like hail, snow ,mist, drizzle, rainfall .etc
affects forests and agriculture the most. Hence, it is important to have a
100
knowledge of the methods of measuring rainfall and analyzing the rainfall
data.
The amount of rain which falls on a level surface is expressed in
mm/hr. The intensity of rainfall is the rate at which it falls during a given
period of time.
Measurement of Rainfall
To know the quantity of rain received in an area at a particular time. Rain
Gauge is used for its measurement.
Rain Gauges are of two types
a) Non Recording gauge Symons Rain Gauge.
b) Recording gauge
Here the amount of rain that falls with respect to time is suitably
recorded on a graph paper.
Three types of recording mechanisms
a) Floating type gauge.
b) Weighing type gauge
c) Tipping type gauge
Symons Rain Gauge:
The Symons Rain Gauge is a metal Cylindrical vessel of 12.5 cm(5")
diameter connected to a funnel and has capacity 100 cm3 of water. The funnel
catches rainwater and is collected in the vessel.
The rain gauge is fixed on a ground surface open to the sky with mouth
75 cm above the ground surface. In plains, one Rain gauge per 520 ha, In
hilly areas one Rain gauge per every 130 ha is set up to measure rain fall.
The intensity of rainfall is not uniform in the area. Hence 2 o 3 raingauges are
to be installed in the area and measure the rainfall.
101
Three methods are adopted to measure the average rainfall.
1. Arithmetic mean method Sum up the rainfall recordings in all the rainguages installed in that area and
take the average - this is easy method to be adopted.
2. Theissen's method or Theissen's polygon weightage method
3. Isohyetal method.
Relationship between Intensity and Duration of Rainfall:
Frequency of rainfall (Repetition of rainfall over a long period)
It is a common experience that the most severe rainfall lasts only for a
short time' The rate at which rainfall occurs during a given period of time is
known as Intensity expressed in mm/hr .The length of storm or the time upto
which rain occurs is called duration. Normally intensity decreases with time.
The Intensity is an inverse function of its duration i.e. the longer the duration
of rainfall, the lesser the intensity.
It is found that the intensity of rainfall in a particular station will be
greater. When moore years are considered( 20,= 200 years) than for a short
period 1 to 5 years.
102
Frequency of rainfall
Frequency of rainfall (Repetition of rainfall over a long period)
Frequency of rainfall is usually expressed as the number of
precipitation days per year. To calculate maximum expected rainfall for a
particular recurrence interval, the following procedure is adopted.
The recorded readings of rainfall of a particular rain gauge station are
arranged in descending order of intensity and the amount of rainfall in that
year.
100mm/hr
80 mm/ hr
60 mm/hr
40 mm/hr
20 mm/hr
10 mm/hr
If the' N' is the number of years for which rainfall records have been
kept.
'R' is the recurrence interval or return period in years
'n' is the ranking of the severe storm.
Then N is given by the fallowing relationship N=Rn
For example, rainfall records have been kept for a particular period of 50
years and it is desired to select the storm that will occur once in 10 years.
In the above formula, R = 10 ; N = 50 ; n =?
n = 50/10 = 5
103
Here all the rainfall incidents are arranged in the descending order of
intensities is the required one. ie ,the 5th severest intensity 600 mm/yr is
expected to occur once in 10 years i.e the lesser amount of rainfall occurs
frequently. To use this method, it is necessary to have rainfall data over a
longer period of years.
Effective precipitation:
That amount of precipitation is to be effective which is available to
plants for their growth. It does not count the water lost through deep
percolation or surface run off.
HYDROLOGICAL CYCLE
Its influence on the growth and development of forest cover over various belts
of India
Water vapours in the
atmosphere
To the earth as
precipitation
Interception and
stem flow
Evaporation
Evaporation
Evaporation
Surface
flow
Steam flow
Oceans
Ground
water
Soil
moisture
By solar energy
Importance of hydrological cycle
1. Hydrological cycle assists the gaseous cycle like N-cycle and C-cycle
important for plant growth
2. Major life supporting system to plants and animals and man
3. Controls world climate and weather
4. Determines the flood and drought conditions of the world
5. Water is always available for living organisms
6. Determines the water quality of the fresh water, reduces the extreme
saline conditions of coastal waters
7. Nutrient cycling
8. Controls evapotranspiration
104
9. Controls global surface temperature
10. Causes rainfall on the surface of the earth
Precipitation and temperature are the major determining factors for the
distribution of natural vegetation in the country. Amount of rainfall differs from
place to place and from season to season in India.
Due to large variation in climate and geographic conditions, the Indian
Sub-continent basically represents six biotic regions or biomes. A biome or
biotic region is a region of living organisms which are characterized by the
characteristic structure of dominant vegetation, climate, animals soil type
similar in nature. Each is collectively recognized as a single large community
unit. The biomes have clear cut boundaries.
Of the total geographical area 329 million Ha. of India, forest coverage
is 23.43 per cent. This is much below the average of 30.4 per cent of the
world.
1. Mountain Biome (complex zonation)
2. Northern Coniferous Forest Biome
3. Desert Biome
4. Tropical Scrub Forest Biome
5. Tropical Deciduous Forest Biome
6. Tropical Rain Forest Biome
1. Mountain Biome
Also known as Alpine Forest Biome. Occurs at higher altitudes in the
Himalayas (Ladakh), including the Sub Himalayan tract from Kumaun to
Kathmandu
105
Elevation varies from 11000 ft to 16000 ft. Rainfall varies from 10002500 mm/year.
Timber line exists at 11000 ft, greatest height at which trees grow
beyond which herbs, lichens and mosses only thrive. At 15000 ft height snow
line prevails beyond which only snow and ice is present. Tree line and timber
line are synonymous.
They do not support uniform vegetation due to altitude, temperature
variation, aspect (low sunlight), and effect of desiccating wind. The
characteristic trees are the high level silver fir
Abies pindrow (silver fir), Betula utilis (silver birch), B. alnoides (Indian
birch),Juniperus communis, J. macropoda, Rhododendron arboretum
(rosewood) etc.
The biome comprises of a mixture of coniferous and broad leaved trees
in which the coniferous trees attain a height of about 30m while the broadleaved trees reach only 10m. Fir, Kail , Spruce, Rhododendron, Plum, Yew
etc. are important species. Altitudinal zones of vegetation in the Western
Himalayas are shown in diagram:
Snow & Ice
15000 ft
Snow line
Alphine meadow : herbs, lichens and
mosses’ junipers, highe level silver
Alpine
11000 ft
Timber or Tree Line
Temperate
Tropics and
sub tropics
5000 ft
Mixed deciduous forest; dry bamboo, shorea
robusta, butea frondosa, Butea mono sperma
Altitudinal zones of vegetation in the Western
Himalayas
106
The greatest height at which
tree grow, mixed coniferous
tree, deciduous broad leaved
tree
2. Northern Coniferous Forest Biome
Also known as Taiga Forest. Occurs in the temperate zone of western
and eastern Himalayas. Here the rainfall is 150cm to 250cm. it mainly
composed of coniferous species. Dominant conifers are Pinus, Cedars, Silver
fir, Spruce etc. the flexible branches of conifers can bend under the burden of
snow. The characteristic trees are: Cedrus deodara (deodar), Pinus
wallichiana (Indian blue pine), Pinus exelsa, Pinus roxburghii (long leaved
pine), Abies pindrow (Himalayan Silver fir). Taxus baccata (common yew),
Picea morinda (Himalayan spruce).
3. Desert Biome
Approximately 35 million Ha. of desert area are distributed in
Rajasthan, Gujarat and Haryana. Annual rainfall is less than 50cm, low
humidity (50%) and high temperature are the features. Only Tropical Thorn
Forests are found. The trees are low (5 - 10m maximum) are widely scattered.
Soil is dry, organic matter content is very less, SiO2 content is high. Large
stretches of land are barren without any vegetation. Thorny shrubs and
bushes, xerophytes, succulent cacti (plants that store water in their tissues
having no leaves for evaporation of water), xerism is due to hot and dry
climate. Euphorbia and Agave, stunted trees like Acacias are common with
scrubs and xerophytic bushes.
4.Tropical deciduous and Scrub Forest
Also known as monsoon forests. Major biotic region of India, covers
approximately 60% of geographic area. Occurs in Gujarat, Maharashtra,
Madhya Pradesh, Uttar Pradesh, Rajasthan. Bihar, Orissa, Karnataka, Andhra
Pradesh and Tamil Nadu. Annual rainfall 50-100cm due to rain shadow effect
of the Western Ghats.
The soil is rich in organic matter and nutrients because of deposition of
leaves on the soil. The roots of deciduous trees act as nutrient pumps drawing
nutrients up from the sub soil to the leaves which are then deposited on the
ground.
Trees of this forest drop their leaves for 6-8 weeks during spring and early
summer when sufficient moisture for leaves is not available.
Vegetation
Tecctona grandis
Shorea robusta
Madhuca indica
107
Pterocarpus marsupium
P. inicus (Padauk)
Laurus nobilis
Albizzia lebbeck
Scrubs
Zizypus spp.
Prosopis spp.
5. Tropical rain forest biome/Tropical evergreen forest
This biotic region includes the rain forest of Malabar, north eastern
states and Andaman and Nicobar island. Annual rain fall exceeds 250-300
cm, annual temp.25-27° C, average humidity of more than 77% Trees don't
shed their leaves and termed as evergreen forest. These are lofty very dense,
multilayered forests and mesophytic evergreen. The sun light cannot reach
the ground and owing to deep shade, the undergrowth is formed mainly of
tangled mass of canes, bamboos, ferns, climbers, laterite soil composed of
red clay occurs acidic in reaction. Well supplied with organic matter .and
hence nitrogen. Climbers and hence epiphytes show profile growth, having
roots on the surface of other plants rather than in the soil. Tall trees have
shallow root system but have wide base (butresses) to provide support dense
canopy that blocks much of sunlight and hence ground vegetation is absent.
Characteristic tree species:
Dipterocarpus indicus
Rhododendron arboreum
Diospyrus ebenum
Sisso
Champa
Hopea parviflora
Callophylum tomentosum
Callophylum apetulum
Mangifera indica
Large tracts of these forest have been cleared for shifting cultivation or
have been replaced by plantation of species .The productivity of Indian forest
is 0.53.meter cube /ha compared to the world average of 2.1 meter cube per
ha. The per capita forest area in the country is 0.11 ha as compared to global
108
average of 0.8 ha. Of the total geographical area of 329 M ,ha of India the
forest coverage is 23.43 per cent. This is much below the average of 30.4 per
cent of the world.
Distribution of rainfall in India
Amount of rainfall differs from place to place and from season to
season in India.
1. Region of heavy rain fall (more than 200 cm)
Western coastal plains
Western slopes of Western Ghats
The southern slopes of khasi and
Jaintia hills, Assam and west Bengal
2. REGIONS OF HIGH RAINFALL (100-200CM)
Himalayan region from Kashmir to west Bengal, Ganga valley (Bihar
and U.P.) Orissa, A.P, T.N, (South), Maharastra, Karnataka and Gujarat.
3. REGIONS OF MODERATE RAINFALL (50-100 CM)
UP, Haryana, Punjab, East Rajasthan, A.P, T.N. and Karnataka.
4. REGION OF SCANTY RAINFALL. (LESS THAN 50CM)
Region of very dry condition such as semi desert or desert area J&K,
Punjab (South) Haryana, central parts of Karnataka, Maharastra.
Rainfall in India
Rainfall in India is monsoonic type 85% of rain is received from
southwest monsoon. Unevenly distributed, Heavy rainfall cause erosion and
flood. The rainfall is mainly of orographical type. most of the rain is received
from in-blowing wind which are forced to rise because of high mountain range
on their path. Therefore rainfall is heavier on the windward slopes than on the
leeward slopes or rain shadow areas eg. Deccan Plateau. Some of the rainfall
is cyclonic and some are convectional. During winter, western parts Ganga
plain get rainfall from the temperate cyclones which originate over the
Mediterranean sea and move towards India through the Persian gulf. The
coastal areas get rainfall which develops during summer and winter. Due to
excessive heating of land during summer, southern parts of the peninsular
region get convectional rainfall.
109
India’s economy depends on monsoon rainfall. 80% of total cropped
area in India depends on rains. If monsoon fails, agriculture is badly affected,
The green belt of the forest becomes dry. During drier months and in less
rainfall areas irrigation is done from rain water in wells, tanks and reservoirs.
One fifth of total power generated in the country is in the form of
hydroelectricity. The generation depends on rainfall. As a result, industries,
trade and commerce are badly affected.
Kinds of rain
There are 3 kinds of rain
1. Equatorial or convectional rain.
In the equatorial regions due to intense heat of the sun the air becomes
hot. Therefore it picks up a great deal of moisture, becomes light and rises.
On reaching the upper region it cools down. As the moisture laden air gets
cooled in upper region condensation takes place and there is heavy rainfall.
Such rain, caused by the rising current of air, is called convectional rain as in
the case of Congo, Amazon valley and Indonesia.
2. Relief or Orographic rain
When moisture laden winds strike against mountains, they rise up
expand
cool down and causing rain. Such rain as is caused by the winds striking
against mountains is called relief rain or Orographic rain, such as the rain in
Western Ghats or on the southern slopes of the Himalayas.
110
3. Cyclonic rain or Frontal Rain
Rain brought by cyclones is called as cyclonic rain, such as the winter
rain in Punjab and Hariyana.
Rain shadow:
The side of mountain where the moisture laden winds strike and
causing rain is called windward side, while the other side which is
comparatively dry is called as leeward side. The rainless area on the other
side of mountains is called as rain shadow.
Estimation of peak runoff rate in a watershed
Methods of runoff computation
Accurate computation of runoff amount is difficult as it depends upon
several factors concerned with atmosphere and watershed characteristics to
evaluate which effects runoff is not so easy. On the basis of field experiences
and observation the following methods are frequently used in the field of soil
and water conservation for estimating the maximum or peak runoff rate of a
particular watershed to design the conservation structures.
The four features of a watershed are
The relief, the soil infiltration, the vegetal cover and surface storage
The proportion of rain which becomes runoff depends on many factors
The topography, the vegetation, infiltration rate, the soil storage capacity, the
drainage pattern are just some of them.
Estimates of rates of surface runoff depend upon two processes;
A. Estimate of the rate of rainfall and
B. An estimate of how much of the rainfall becomes runoff.
Prediction of peak rate of run off
There are three main methods commonly used in arriving at the peak rate of
runoff:
1. Rational method
2. Cook's method
3. Hydrologic soil cover complex method
The following basic assumptions are made in deriving the above
methods-:
111
a. Rainfall occurs at uniform intensity for a duration at least equal to the time
of concentration of the water shed.
b. Rainfall occurs at uniform intensity over the entire area of the watershed.
Among the three methods, the first method is less complicated and widely
used in our country. So we will restrict our discussion to rational method:
1. Rational method
This method is the oldest, simplest and possibly the most consistent one in its
ability to adjust with the new concepts and developments in evaluating water
shed conditions. This method is expressed by an equation.
Q peak = CIA/360 Cu m/sec
Q = Peak rate of surface runoff in cubic metre/ sec
C = Runoff coefficient
I = Intensity of rain in mm /hr for the design recurrence interval (T) and for
duration equal to the time of concentration (t) of the watershed.
A
= Watershed area in ha
C
= Runoff coefficient
= The ratio of the rate of runoff to the rate of rainfall.
If half of the rainfall is lost by infiltration etc., and the others half
appears as runoff then the coefficient denoted by C is 0.5..
The application of formula consists of selecting appropriate vales of C, I , A.
1. The area "A" can be measured by surveyor from maps or aerial
photographs.
2. The vales of "I" is worked by using the equation
I = KTa
(t+b)n
I = Rainfall intensity mm/hr
T = Recurrence period or return period in years
t = Duration of storm in hours or time of concentration (will coincide with
maximum rate of runoff)
k, a, b and n are constants and the values of these constants have been
worked out for different zones (southern , eastern , western and northern and
different stations within the zones) in our country.
112
The vales of 'c' can be picked up from runoff coefficient table which has
been worked out. The main advantage of the rational formula is that it can
always be used to give an estimate of maximum runoff rates, no matter how
little recorded information is available. Naturally the precision of the estimate
depends upon the precision of information put in.
For a given duration (time of concentration) and for particular return
period, the maximum intensity of rain fall can be worked out. The value of T or
return period
has to be decided by type of concentration, we are going to have.
Example:
Predicting peak rate of surface runoff using the rational formula
Estimate peak rate of surface runoff for 15 years frequency for 40ha.
Watershed which is under the following classes of vegetation cover slope and
soils texture; 27 ha of area is cultivated and flat and with clay and silty loam; 5
ha of area is grazing land with rolling down slopes and stiff clay; 8 ha of area
is over hilly area; under forest cover with sandy loam soil. The area is located
in southern zone. The maximum length of run is approximately 1600m and the
elevation of the highest and outlet points is 300 and 200m respectively.
Solution:
A. Find out the value of 'C' form table
1. Cultivated land flat and clay and silt loam: 27ha; C; 0.50
2. Grazing land - rolling down slopes and stiff clay 5ha: c= 0.55
3. Forest, hilly area with sandy loam soil: 8ha; c= 0.30
Weighted average of the above:
= (0.5x27) + (0.55x5) + (0.30x8)/ 27+5+8
= 13.5+2.75+2.4/40
= 18.65/40
Valve of C = 0.47
Rainfall 750mm
Q
= CIA/360
=0.42 x 750x40/360
=38.1 cum / sec
TMC = 38x35x60x60x24
109
113
=0.115 tmc
Irrigated area = 0.115 x 4000ha.
If the value of I not given, the value of I is found out by using the
equation,
Find out the value of I
I = KTa
(t+b)n
Value of k, a, b, and n are picked up from table. k=6.311
a = 0.1523
b = 0.50
n = 0.9465
Recurrence Period T = 15 years.
The value of 't' time of concentration (duration) has to be found by
using the equation given below:
't' (in minutes)= 0.01947 K 0.77
K= L3
H
L =1600
H
= 300-200= 100
= √1600 x1600 x 1600
√100
= 40 x40 x40
10
K= 6400
t= 0.01947 x (6400)0.77
= 0.01947 x (0.77 log 6400)
=0.01947 x 852.5
=16.598 or
= 17 minutes
Convert these 17 minutes to hour, which becomes
t= (17/60) hour.
114
So, we now know the values of all variables in equation
I = KTa as follows
(t+b)n
K=6.311
T= 15
a =0.1523
b =0.50
n =0.9465
= (17/60) hours,
Substituting these values in the equation
I = KTa
(t+b)n
=
6.311 x 15 0.1523
[(17/60) + 0.50]0.9465
= 6.311 x1.51
0.78 x 0.9465
=
9.53
0.7902
= 12.06 cm/hr or 120 mm/hr
(iii)
Area with value of A
Find out the value of Q
Now, substitute the values of C, I, A in formula
Q= CIA
360
= 0.47 x 120 x 40
360
= 2256
360
= 6.26
Peak Rate of run off is 6.26 or 6.25 cu. metres /second
On an average, the discharge of water per day in terms of TMC
TMC = 35 x6.25 x 60 x 60 x 24
(10)9
115
= 1,89,00,00,000
100, 00,00,000
= 1.89 TMC
COOK'S METHOD FOR PEAK RUN OFF RATE ESTIMATION
This method consists of evaluating the four watershed characteristics
viz; Relief, Infiltration rate, vegetal cover and Surface storage. For these
characteristics numerical values are assigned for computing the runoff. The
values are mainly given on the basis of observation and comparison of the
above features with similar conditions of the watershed.
This method is sometimes called Cook's method, after the engineer of
US. Soil Conservation Service; who developed it. It is also known as the ΣW
method (pronounced Sigma W) because Σ
is the mathematical sign
indicating the summation of several values and W is the watershed
characteristics and the method consists of summing numbers (summing the
numbers of each characteristic which contributes to a part of quantum of run
off), each of which represents the extent to which run off from the catchments
will be influenced by a particular characteristic.
The effect of four features is considered; the relief, the soil infiltration,
the vegetal covers and the surface storage. Each of these is considered in
turn, and the condition of the catchment is compared with four descriptions
shown in the table. The description is chosen which most nearly fits the
catchment and the corresponding numbers (shown in brackets) noted. If the
catchment condition lies somewhere between two adjacent descriptions in the
table, intermediate values may be interpolated. The arithmetic total of the four
numbers is the catchment characteristics (U S watershed characteristics) and
will lie between extreme values of 100 (if the higher number has been chosen
for each parameter) and 25 (if the lower value has been chosen in each
case).
Table: Catchment Characteristics for Cook's Method (USA)
Relief
100 (extreme)
(40)
Steep, rugged
terrain with
average slopes
generally above
30%
75 (high)
(30)
Hilly, with
average
slopes of 10 –
30%
116
50 (normal)
(20)
Rolling with
average slopes
of 5-10%
25 (low)
(10)
Relatively flat
land with
average
slopes of 0 5%
Soil infiltration
(20)
No effective soil
covers, either
rock or thin soil
mantle of
negligible
infiltration
capacity
Vegetal cover
(20)
No effective
plant cover;
bare or very
sparse covers
Surface
storage
(20)
Negligible
surface
depressions;
few and
shallow;
drainage ways
steep and small;
no ponds or
marshes or
tanks
(15)
Slow to take
up water; clay
or other soil of
low infiltration
capacity IR
0.25 – 0.75 cm
/hr soil is hard
clay
(15)
Poor to fair;
clean
cultivated
crops or poor
natural covers
less than 10%
of drainage
area under
good cover
(15)
Low well
defined system
of small
drainage ways;
no ponds or
marshes.
Surface
depression is
very low.
(10)
Normal, deep
loam with
infiltration equal
to prairies soil
IR – 0.75 – 2.0
cm/hr Normal
and deep
permeable soil
(10)
Fair to good;
50% of
drainage area is
grassland or
woodland not
more than 50%
of area in clean
cultivated crop.
(10)
Normal,
surfaces of
considerable
depression
storage, lakes,
ponds and
marshes less
than 2%
drainage area
(5)
High deep
sand or other
soil that take
up water
rapidly IR >
2.0 cm/hr
(5)
Good to
excellent
about 90% of
Drainage
area is good
grass land or
forest
(5)
High surface
depression,
storage high
drainage
system are
not sharp
10% of area
with lakes
and ponds.
Lower the numerical value of each characteristics, lower the peak rate-run off
Higher the numerical value of each characteristic, higher the peak rate run-off
For computation of run-off, the next step. is to obtain the sum of all numerical
value (ΣW) and then uncorrelated run off is determined, using the run-off
curve as shown in figure, against the sum of the numerical value. The run off
determined so is valid for 10 years recurrence interval. Again this value of run
off is modified for geographic location of the given watershed and for the
desired recurrent interval. This is done by using following formula:
Q = PRFS
Where
Q = peak run off rate in cum/sec for a specified geographic location and for
desired recurrence interval
P = uncorrelated value of run off i.e. obtained from run off curve
R = geographic rain.-fall factor
117
F = recurrence interval factor
S = shape factor of watershed
Example
Find out the peak run off for the period of 25 years recurrence interval from a
watershed area of 40 ha having the following information regarding its
characteristics:
Problem
Land use
S.No.
area in
ha%
1
cultivated
25 ha
2
1
Infiltration
capacity
cm/hr
0.75
5
1
Slope %
Pasture
land
15
ha
Vegetal
cover
Surface
storage
Less
than
10%
area
under good
grass cover
About 90%
area is under
grass cover
Ponds
are
less than 2%
of
drainage
way
Very
low
surface
depression
Assume
1. length and width ratio= 3
2. rainfall factor (R) = 1
3. frequency factor (F)= 1.3
4. shape factor (S)= 0.8
Solution
Using table 2.4 the numerical values for four different watershed
characteristics are determined as given under:
Soil
Vegetal Surface
Total
Land use
Relief
interaction
S.No.
cover
storage
(1+2+3+4)
area
1
2
3
4
1
Cultivated
2
15
15
10
42
25 ha
2
Pasture
10
7
5
15
37
land 15 ha
Weighted numerical values
= 42x25+37x15
25+15
= 38.62 OR 39 = 40
Shape factor (S) = 0.8
118
Multiply by 0.8 for a long and narrow catchments. The distance between
upper catchment and lower catchment is long and 1.25 for broad and short
catchment.
Rainfall factor (R)
A measure of the relationship between temperature and precipitation
designed to provide an indication of the climatic aridity of the region
Frequency factor (F)
The rate of recurrence of an event in periodic motion or number of
cycles per time interval in periodic motion.
Graph
(3 dimensional graph)
x-axis watershed area in ha.
Y-axis peak discharge in m3/sec
z-axis watershed characteristics Σ w
119
A standard graph is drawn for various Σw values between watershed
area and peak discharge in m3/ sec, after that the values of uncorrelated peak
run off using the above standard graph against Σ w= 40 is determined which
is 2.05m3/s.
Correlated peak run off Q =PRFS
= 2.05x1x1.3xO.8
= 2.13 m3/s
Water available in one year (two seasons)
= 2.13x35x60x60x24x100 TMC
109
120
SECTION D - WATERSHED MANAGEMENT
SOIL CONSERVATION AND LAND MANAGEMENT
Soil formation as a result of weathering of rocks and decomposition of
organic matters takes place very slowly. It takes about hundreds of years to
form 1 cm thick of soil but the rate of loss of this soil is very rapid. 1 cm thick
layer of soil may be lost n one season, if soil is unprotected and soil erosion is
fast.
Forest department therefore has to take various soil conservation
practices as a part of land management besides regular work of forest
management
Soil is the uppermost weathered and disintegrated layer of the earths
crust. The average depth of the soil in the world is 15-30 cm. This layer of soil
supports all plant, animal and human life. This layer of soil being washed
away by wind and water aided with other agents like temperature and
biological. This washing away of soil is called soil erosion.
Soil erosion - definition:
It is the loosening of soil from bed and transportation of soil material
from one place to other.
•
denotes the removal of the soil from the place where it was formed to
other places by wind and water.
•
Wearing and tearing of soil along with its sweeping away is called soil
erosion. By too much erosion of soil the land becomes unsuitable for
cultivation and afforestation.
Soil erosion in India
In India the soil loss due to erosion is estimated as 6000 million tones
per year i.e, an average of 17 tone/ha/year.
According to Dr. M.S swaminathan former Director General of ICAR,
about 6000 million tonnes of valuable soil is either washed or blown away
annually resulting in 2.5
million ha. of agriculture land becoming unproductive.
Tree cover checks soil erosion and stabilizes ground water level.
Out of this soil loss 24% of soil is carried to sea through rivers and 10%
of soil material is carried to lakes and reservoirs thereby reducing their
capacity by 1 to 2% every year. As a result the life of reservoir is reduced from
200-300 years to 50-100 years.
121
Factors influencing erosion:
1. The amount and intensity of rainfall and wind- erratic and heavy rainfall.
2. Removal of vegetation cover thereby exposing the soil surface.
3. Indiscriminate felling of trees.
4. Excessive grazing (biotic interference).
5. Forest fire.
6. Faulty management and improper and unscientific cultivation practices, e.g.
ploughing along slope.
7. Slope of the land (more the slope, more run off and more erosion.
8. Nature and properties of soil (i.e soil properties viz. texture, structure less
organic matter content less infiltration capacity, less porosity, less CEC).
9. Failure to control surface run off.
10. Conversion of forest lands into agricultural lands (shifting cultivation)
11. Encroachment of forest and grassland to meet food, fuel and fodder
needs
12. Surface mining for exploitation of natural resources.
13. Unscientific methods of disposal of mine spoils. The countries safety food
security and economy lie in the management and conservation of natural
resources viz. soil, water and vegetation.
14. Man and animals
Man and animals when move from one place to another remove the
soft soil. Sometimes, man is making houses canals, etc. and animals in
making burrows etc. also helps soil erosion.
15. Heat and cold
In deserts there is great range of temperature. It causes more
expansion and contraction and hence makes the soil week. The expansion
process also takes place in freezing of water in pits and fissures etc.
Management of soil Erosion
1. Damming the rivers-by construction of water harvesting structures like farm
pond, percolation ponds, and irrigation tanks, construction of dams, etc.,
2. Afforestration.
3. Restricted grazing
122
4. Management of slope of land
By construction of terraces, trenches, contour bunds, contour furrows,
contour cultivation, adoption of biotechnical method in sloppy forestlands for
stabilization.
5. Improvement in methods of cultivation
Ploughing across the slope.
Same type of crop should not be grown time after time and also should
grow short period ripening crops.
Types of erosion:
1. Erosion of soil by water
2. Erosion of soil by wind, is also called as layer erosion, sand drift or wind
drift or soil blow.
Land degradation is mainly caused by water erosion (90 m.ha), wind
erosion (50 m.ha) water logging (20 m.ha), salt affected land (7 m.ha)
Water erosion in forest:
Reserved forests are not affected by erosion hazards, since they are
scientifically managed. Other kinds of forests (like protected and unclassified)
are affected to a large extent by erosion.
Dense natural vegetation (forests) intercepts rainfall and thus nullifies
the impact of raindrops. Both forests and grassland cover contribute organic
matter residues. These are incorporated into the surface soil, thus giving
greater aggregate stability and absorptive capacity in the soil. Plant roots hold
the soil intact and prevent erosion when the run off is great.
Wind has been an erosive agent and wind erosion gives a serious
problem in arid and semi arid areas, which are barren and devoid of any
vegetation.
The soil loss by wind erosion is usually considered negligible in forest
soils supporting vegetation.
Erosional process due to wind erosion or sand drift :
1. Abrasion: Air currents armed with sand grains scarp polish or etches away
rock surfaces.
2. Attrition: Mutual wear and tear of rock and sand particles.
3. Deflation: Lifting and blowing away of loose materials from the ground.
123
Land forms of wind erosion
1. Sand dunes: are formed by the deflation action of wind that deposit sand in
ridges. Barchan is a famous dune, which is of crescentric shape or moon
shape and is a special type of transverse dune.
124
2. Loess:
The fine dust blown beyond the desert limit is deposited on
neighbouring land as loess. It is a yellow friable material and is usually very
fertile. Noted examples are found in Northwest china and parts of mid-west
U.S.A.
Aeliaon Land forms due to wind action
Types of deserts:
1. Erg or sandy desert
2. Reg or stony desert
3. Hamada or rocky desert
Control of wind erosion:
1. By covering the ground surface with vegetation so as to hold the soil
particles moving in saltation.
2. The sand dunes may be covered with suitable vegetation which should be
drought resistant, wind firm, fast growing and capable of producing sufficient
seeds for its further natural regeneration.
3. Planting dense vegetation or establishing a wind break of
- vegetation like tenacious grasses and shrubs on the eroding fields at
right angles to the most erosive winds.
- Regions of low rainfall are left safely in native grasses.
- vegetative barriers such as tree shelter belts and wind breaks are
effective in reducing wind velocities for short distances and for trapping
drifting soil.
Single row wind break:
It indicates a row of trees planted in a line to protect the cultivated crop
from wind.
A single row / line of trees or shrubs or mixture of both is planted
around the sides perpendicular to the direction of prevailing erosive wind as a
protection against dust storms in summer and snow storms in winter. It covers
a wide and large area and sometimes covers the whole region on a planned
pattern. Wind break may be of even single row of only one species and
protects only small gardens.
125
Poplars and Eucalyptus are best suited for this type of single row. They
can be planted at 2.0-2.5m spacing and their spectacular growth soon forms a
fine wind break. One drawback is if one individual dies or loose their branches
gap appears.
In planning the wind break, the height and density of trees shrubs are to be
considered.
The wind is abated over a distance equal to about 10 to 20 times the
height of the barrier, a quarter of the protected area being on the windward
side and three quarter downward of the barrier. e.g., height of the barrier is 20
m, then the distance upto which the particles deposited is 400m.
Species suitable for wind breaks: Prosopis chilensis, Casuarina
equisetifolia,Ailanthus excelsa (tree of heaven,
used for match
industries),Albizzia lebbeck (kokko tree, lebbek tree), Eucalyptus sp.
Shelter Belt
•
Belt is a belt of trees and/ or shrubs planted around the sides
perpendicular to the direction of erosive wind for the purpose of
shelter from wind, sun, cold, snow, sand, drift etc. Shelter belts
are generally extensive and will cover large areas.
They block the wind or reduce the wind velocity and decrease soil
erosion and decrease damage to the crops caused by wind blown dirt
particles.
126
Species selected should be able to come in the climate and soil, fast
growing, easy and early establishment, wind firm and should give marketable
products.
Shelter belt should comprise of different species with a triangular
cross-section or like circus tent. Hence tallest trees should be planted in the
centre and shorter trees on the both sides of the centre. Low shrubs and
spreading shrubs may be in edges.
Width of shelter belt should be 15 to 30 metres with 5 or 7 rows with
one type of tree in a row. Rows may be of 2 to 3 m. apart Central row should
be tallest trees. Length of row may be as long as possible.
Mixed stands can be difficult to handle and maintain, since some
species try to suppress others and sometimes may even help another species
to become established.
Functions of shelter belt
In addition to stopping sand drift and avoiding damage to crops by wind
erosion, the shelter belt improves soil subsequently due to the addition of
organic matter by way of leaf fall and provides shelter for wild life.
-some minor produce is got.
-temperature is reduced.
-rate of evaporation is reduced.
-more moisture is supplied to crops.
-there is increase of yield by15 to 25%.
Suitable tree species for Shelter Belt :
First row
Shrubs grown in bunches of low height viz., Agave americana
(centuary plant,stout shrub)
Agave sisalana (Sisal,xerophytic perennial with a short thick stem
).lpomaea carnea (Railway creeper, a climbing shrub) Vitex negundo (
Chinese taste tree, a shrub or small tree grown for reclamation of forest land
and possess insecticidal properties and used in ayurvedic preparations.
Second row
-tree with broad crowns viz.,
127
Pongamia pinnata (Pongam tree,seed oil used for soap making, in the
treatment of skin disease and rheumatism and leaves are used as manure
and fruits are edible.)
Cassia siame (Kasod tree-ornamental tree with yellow flowers) Acacia
catechu( Catechu tree - small tree).
Third row
-Tall growing tree with stability such as
Dalbergia sissoo (Sissoo tree, wood used for making musical, instruments viz.
Natheswaram, Veena, keys of sitars)
Albizzia lebbk, Eucalyptus sp., Casuarina equisetifolia etc.
Fourth row
-Tall growing tree e.g. Ailanthus excelsa ( tree of Heaven, wood for match
industries
Fifth row
-Permanent slow developing species, fruit producing plant- horticultural crop
eg Citrus limon-citrus or lemon, sapota – sapodilla.
The foliage exposed to the wind should be in the form of a circus tent
for the purpose of lifting the drifted soil particles well above the ground level
and dropping it gradually downward on the leeward side of the planting.
It is observed that the wind velocity near the ground on the leeward
side is abated over a distance equal to about 10-20 times the height of the
barrier.
TYPES OF WATER EROSION
Two types of erosion1. Geologic erosion/normal erosion/natural erosion: Caused by the agents of
water and wind-erosion not caused by anthropogenic causes but by natural
calamities influenced by climate and topography.
2. Accelerated or unnatural erosion : Caused by man's activities during
ploughing and tilling of soil, building construction.
Water erosion or soil wash is predominant in plains where the rainfall is >900
mm/year and rainfall intensity is 25mm/hr. This type of erosion is prevalent in
almost all the places of Tamil Nadu. The amount of soil erosion by water
depends on the combination of two factors:
128
a) The power of rain to cause erosion
b)The ability of the soil to withstand erosion.
Erosion is a function of erosivity (of the rain ),and erodibility (of the
soil).This erodibility factor depends not only on the soil, but also on the crop
management practices adopted on the soil.
Erodibilty = %sand + %silt
% clay
Erosion = f(Erosivity)x(Erodibility)
(Erosivity= potential ability of the rain to cause erosion
Erodibilty=vulnerability of the soil to erosion i.e. susceptibility to erosion.)
&
Combining these two factors, erosion of soil i.e.soil loss may be
calculated based on the Universal Soil Loss Equation (USLE),developed by
Wischmeier and Smith (1965).
Universal Soil Loss Equation (USLE):
(Wishchmeier and Smith, 1965)
A=RxKxLxSxPxC
Where, A=Estimated average annual soil loss in tones/ha /annum
R= Rainfall or run-off factor in joule/ha
K= Soil erodibilty factor
(1 joule = 10000000 ergs )An erg is the quantity of work done when two
point of application of a force of one dyne is moved through a distance of 1
cm in its direction. Since erg is a small quantity, the big unit joule is used.
L=Length of the land in that region (m)
S=Slope or steepness factor (%)
C= Cropping management factor (dimensionless)
P=land management factor (dimensionless)
This equation can be used to predict long term average annual soil loss
under specific Land use and management practices.
Length of slope is longer and the degree of slope is acute, a large
quantity of rain will fall on it. If the rate of rainfall exceeds the rate of
infiltration, there will be large accumulation of water at the base or flows out
as run off or overland flow.
129
FORMS OF WATER EROSION
Three forms of water erosion 1. Pre-channel form of erosion:
(a) rain drop erosion / splash erosion which leads to puddle erosion and
fertility erosion.
Puddle erosion
The breaking action of rain compact the soil thereby forming
impervious layer of surface mud. The compacted surface results in more run
off.
Fertility erosion
Finer particle are lost gradually leaving behind coarse particles which
are inert and infertile. Hence the fertility is lost as plant nutrients and organic
matter are floated away.
Remedy: application of organic manures and green manures
( b ) Sheet erosion ( inter-rill erosion)
Due to flowing water, the fertile top soil on moderate sloppy lands is removed
in thin sheets or thin layers. This reduces the fertility and productive capacity
is reduced to the minimum. This process will be slow but very dangerous.
Control measures
Crop rotation, strip cropping, cover cropping, mixed cropping, inter
cropping, contour cultivation, mulch farming. Application of organic manures
and green manures.
2. Post- channel form of erosion:
a) Rill erosion; b) Gully erosion; c) Ravine erosion
a) Rill erosion
If sheet erosion is allowed to continue, the silt laden water moves along
well defined small channels which spread out finger like ditches over the
entire field. These are called miniature gullies or Rills. If these are left
uncared, will become deeper and wider, increase in numbers hinder the
usage of agricultural implements and will reduce the yield, thus developing
into a gully.
Control measures
Contour tillage, level terracing, crop rotation, mulch farming, contour bunding,
raising grass crop.
130
b) Gully erosion
Unattended rills get deepened, widened and lengthened every year
and develop into gully. Gully is the deep cut on the land surface caused by
run off in definite channels.
Agricultural implements cannot cross their channels. It is formed due to
water fall erosion at its head and channel erosion on the banks of the gully
added with mass movement of soil.
Remedial measures
i. Forming vegetative check dams across the slope.
ii. Dispose off the excessive run off through protected outlets like diversion
channel or grassed waterway.
iii. Construction of temporary or permanent check dams depending on the
slope and depth.
iv. At the head of the gully, erosion resistant or soil conserving crops may be
raised.
Erosion resistant or soil conserving crops which protect and save the
soil from erosion and conserve organic matter in soil. E.g. grass, pasture,
groundnut.
Soil binding or soil building or leguminous crops
-even after harvest, they provide organic matter and nitrogen to soil and
maintaining soil productivity.
e.g. Bengal gram, Black gram, Green gram, Cowpea, Soybean.
Soil depleting crop or Erosion permitting crop or soil exposing crop -remove
organic matter and mineral nutrients from soil ( Ca, P, K) and give chances for
erosion.
e.g. maize, sorghum, cumbu
Temporary check dams
1. Brushwood check dam
2. Stone-wall check dam
Permeable checkdam
3. Sand bag check dam
4. Gabion-wall check dam
131
5. Earthen check dam ( trench-mound method)
•
used for small gully or wider gully with shallow depth.
•
a separate spillway may be provided
•
the dam should be turfed or pitched with stones in high rainfall areas
•
foundation need not be dug
•
a side slope of 1: 1 should be given.
•
Only a part of the soil dug out from the trench is used to make the
dam/mound
Gully plugging
Temporary check dams in gullies with 2 m width and 1 m depth
( small gully). Expenditure RS.10000-15000
Big gullies
-4 m width and 2 m depth
- Permanent check dam. Expenditure 30000-40000
Cross all 10 – 12 m
Very big gullies
> 4 m width and> 2 m depth
- percolation pond
Storage 1000 m3 to 40000 m3
132
Ravine erosion
unattended gullies Join together and form/develop into ravines.
Ravines are the network of deep gullies.
- the whole plain land mass is cut into a number of deep gullies.
- occur at 6 m ha. in India.
- occur on the banks of river Yamuna ( UP), Mahi ( Gujarat ), Betwa (MP)
Chambal ( Rajasthan ), Kambam ( TN).
Due to deposition of silt, the ravine beds are suitable for growing trees
Successful trees in ravine beds:
Acacia nilotica, Albizzia lebbek, Azadirachta indica Dalbergia sissoo,
Dendrocalamus strictus,, prosopis juliflora.
Albizzia lebbek is suitable for avenue planting, wind breaks and shelter belts
Prosopis sp. will reduce the velocity of flowing water and also retain the soil
particles around the tree roots.
3. Other types of erosion
a) Stream bank erosion / channel erosion
b) Water fall erosion
c) Wave erosion
d) Pot hole erosion
e) Glacial erosion
f) Torrent erosion
g) Pinnacle erosion
h) Landslide erosion / soil slip erosion
Temporary Checkdams
1) Brushwood check dam
2) Stonewall check dam
133
3) Sandbag check dam
4) Gabion wall check dam
The excess surface run off should be allowed to flow through the
centre of the check wall dam. The excess surface run off should not be
allowed to flow through sideways.
Permanent check dam
In the hill slopes, as a permanent structure, check walls should be
constructed across the slope, so that excess run off flows through the centre
of the check wall. On no account, water should be allowed to flow through
sideways.
WATERSHED
Watershed is defined as a land area from which water drains to a given
point or to a drainage basin.
Technically, watershed is a hydrological entity.
134
Different terminologies for watershed:
•
watershed
•
catchment
•
water divide
•
interfluvae
•
water basin
•
river basin
A watershed area may be nearly flat, sloppy, undulating or may include
hills or mountains. A watershed area may be either agricultural land area or
forest area.
The area of watershed may be either 10 ha or 10000 ha. For the
development and efficient management of watershed in about 2 to 3 years,
the area of watershed in forest area should be 400-600 ha ( micro catchment
area) and for cultivated region, the area of watershed should be 1000-2000
ha.
All conservation and developmental works of a place or a region like
tree planting, soil and water conservation works, water harvesting must be
planned and taken up on watershed basis but not on area or region basis.
Watershed management essentially relates to soil and water
conservation and land management. It implies the scientific use of soil and
water resources in the catchment for higher production of food crops and
forest biomass on sustainable basis.
Integrated watershed management is defined as the rational utilization
of land and water resources for optimum production of vegetation with
minimum hazard to natural resources and for the well-being of the people who
dwell within it.
WATERSHED MANAGEMENT PLAN
Watershed is defined as a land area from which water drains to a given
point or to a drainage basin. Technically watershed is a hydrological entity.
Watershed management implies the judicious use of all the resources
i.e. land, vegetation and of water of the watershed to achieve the maximum
production with minimum hazard to the natural resources and for the well
being of the people. The management should be carried out on watershed
basis. The task of watershed management includes the treatment of land by
135
using most suitable biological and engineering measures in such a manner
that the management work must be economical and socially acceptable.
The main objective is to check the soil erosion and reduce the effect of
sediment yield on the watershed and to rehabilitate the deteriorating lands.
Factors involved in watershed management
1. Selection of watershed area
1. Non-forestry area
2. Drought prone area-areas receiving less than 10cm of rain fall or more than
70% of the area is dry land in the region.
3. Desert area.
4. Water deficit area.
5. Tribal area.
6. Compact area of 500ha.
II. Collection of basic information for preparation of a watershed
management plan:
a. General description -location, elevation and area.
b. Watershed characteristics - shape, size, topography, relief, geology-rock
and soil type, drainage, land capability classification, land use pattern(forest,
agriculture and grassland)
c. Climatic characteristics – precipitation and intensity of rainfall, wind velocity,
temperature.
d. Watershed operation -types of watershed works already implemented.
e. Social status of inhabitants inclusive of village statistics.
f. External factors affecting the functioning of watershed e.g. mining, road,
buildings, etc.
g. Water resources and their availability.
III. Watershed management works:
1. Vegetative measures(agronomical measures)
a. Strip cropping.
b. Pasture farming.
c. Fertilizing the crop land
d. Green manuring.
136
e. Growing leguminous plants/crops.
f. Crop rotation.
g. Mixed farming.
h. Mulching and watt ling.
2. Engineering measures (structural practices):a. Gully plugging.
b. Diversion ditches.
c. Bench terraces- either renovation of the existing terraces or construction of
bench terraces.
d. Paving grass waterways.
e. Bunding
f. Provision of water harvesting structures-farm pond and percolation pond
g. Any other structures, like contour furrowing, contour trenching, trash
mulching, etc.
Mulching:- Mulching is a system of farming in which the organic residues like
straw, saw-dust, leaves, plastic film, loose soil etc. are spread on the surface
of the soil around the plant and roots to protect soil and plant roots from
effects of raindrops, soil crusting ,evaporation etc.
Strip cropping:- Growing soil conserving and soil depleting crops in alternate
strips running perpendicular to the slope of the land or to the direction of
prevailing winds for the purpose of reducing erosion.
Soil conserving crops : Grass, pulse cops, groundnuts, etc.
Soil depleting crops:- Corns, sorghum, pearl millets, etc. Its importance is in
controlling the runoff erosion and wind erosion thereby maintaining the fertility
of the soil-universally recognized.
Watershed management comprises of different stages:First Phase: 1. Selection of sites for watershed
2. Benchmark resource survey(survey for identification of
resources availability in the area).
3. Land Capability Classification.
Second Phase: Preparation of watershed development plans (in consultation
with the community).
137
Third Phase: Plan implementation(with community involvement).
Fourth Phase:
1. Monitoring and evaluation.
2. Maintenance of executed earth works.
The entire catchments area is treated with the ridge to valley
approaches. The water is conserved from the source itself.
Development works in a watershed area :
1.In situ conservation of rain water:In micro catchments area :
1. Levelland with low rainfall.
2.ln high rainfall areas of level land.
3. For slope lands- crescent shapes furrows.
V Bunds and crescent bunds
These are structures used for in situ water harvesting for individual tree
crops. ‘V’ shaped or crescent shaped bunds are constructed along downslope
around each tree. These structures are cheaper as compared to contour
bunds and are well suited for tree crops in moderately sloping lands (5% to
15% slope).
(c) In high rainfall areas of level lands, circular basins are formed and
saplings are planted at the centre as shown in the diagram.
138
(d) For sloppy lands, crescent shaped furrows are formed and saplings
are planted at the centre at an espacement of 5 m.
These structure increase the soil moisture status in the area immediately
surrounding the trees.
(e) Summer ploughing, broad bed and furrows, ridges and furrows,
ridges an furrows, random tie ridging, compartmental bunding etc as the
various in situ water harvesting methods for black and red soils cause an
increase of upto 15% in crop yields.
2. Soil conservation works: - Mechanical
Bench terracing for 20-50% sloppy land with high rainfall. Bench
terracing are executed in rain fed lands having a slope between 16 to 33%.
Inwardly sloping terrace formed in high rainfall areas by giving 1 m 40 m drop
towards heel side with toe drain to drain out the excess water safely. It is also
called as reverse slope bench terrace.
Bench terracing is adopted on hill slopes when substantial soil depth is
available. The terrace will have either an inward or outward slope. The width
of the terrace depends on the percentage of the slope; minimum width being
2.0 m is required for cultivation. terracing will facilitate more water to percolate
downwards by reducing the velocity of runoff.
Outward sloping terraces are formed where rainfall is less (<500mm/yr)
and soil shallow (<15 cm depth). The benches are formed with outward slope
of 4%. Shoulder bunds or concrete with spillway arrangements are provided
on the toe portion of benches to slow down the velocity of water and avoid
erosion.
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Outward slopping terrace
Step terrace
Irrigation terrace
Inwardly slopping terrace
For raising rice crop, a raised bund at the outer edge to retain irrigation water.
140
Californian Type Terrace or Puertorican Terrace
Mechanical plus vegetative barriers are kept on the original hill slopes at
convenient distances and the terraces are formed gradually. The length of the
slope is broken into benches by planting wattles at intervals of 5 to 7 m with
each ploughing, the soil is pushed downwards, thus gradually building up the
terrace.
The barriers check the soil so moved from being washed downwards.
In this of terrace, a graded bund of 45 cm ht. is formed and a vegetative
barrier is maintained. A tall stiff and quick growing exotic Guatemala gama
grass (Tripsacum laxum) planted along graded lines in two rows of 30 cm.
apart and 22.5 cm. staggered spacing terrace is formed at stages.
In the Nilgiri hills, where potato cultivation on red laterite soil caused
soil loss of 39 tons/Ha/restoring to simple contour farming brought down the
erosion to 15 tons/Ha/year. Contour bunding at suitable spacing has been
practiced in the Indo-Gangetic plain to reduce excessive run off and resultant
erosion. Cultivation on benches reduced the soil loss to 1ton/ha/yr (Das
1977)
2. Contour trenching
Contour trenches are dug on the contour lines. These trenches are dug
in areas where the soil is impervious. They will intercept and harvest the run
off water and the stored water will percolate underground and also impart the
required moisture for the standing crops in between the trenches. Staggered
trenaches are dug where the soil is very hard.
141
•
are formed for 30 – 75% sloppy lands
(a) staggered trenches (for high rainfall areas where the soils is very hard)
(b) Continuous Contour Trench (CCT)
•
for low rainfall areas and shallow depth and soil is impervious
2. Countour Furrowing
•
for 5 – 10% slopy lands
142
3. Countour Tillage
•
for 2 – 8% slopy lands
The slopes can be stablised by sodding with grasses as Cenchrus
citiaris, Dicanthium annulatum and Eremopogon foveolatus (good fodder
grass). The shallow ravins (<2m deep) have been successfully reclaimed for
agricultural and horticultural purposes. In the east Indian bad lands, resorting
to engineering and biological measures has resulted in increased rain water
retention by 53%.
5. Contour bunds(earthen) :
For 2-6% slopy lands contour bunds are constructed to intercept the
run-off flowing down the slope by providing embankment along the contour
lines, These bunds are the cheapest measure of harvesting rain water and to
conserve it, The contour bunds are usually of less than 1.00 mt. height. Some
of the water stored against each bund will percolate downward to recharge
the groundwater and the intermittent areas between the bunds will get the
required moisture for the standing crops for a substantial period.
6. Compartmental Units
Contour bunds are generally laid in areas where the land holdings are
extensive. Where land holdings are limited the land is generally divided by the
formers-into rectangular compartments both for cultural and owner ship
division. Many farmers have constructed compartmental bunds in their lands.
In terms of water harvesting and soil conservation effects,
compartmental bunds are equal to contour bunds. They differ only in the
layout. Contour bunds and compartmental bunds offer the triple benefits of,
143
1. Enhancing soil status and mitigating water stress
2. Increasing ground water recharge
3. Conserving soil by reducing erosion and trapping silt.
7. Contour stone wall (or Revetment or contour stone building)
Contour stone walls are constructed in the existing plantation areas
having a slope of 33 1/3%, where boulders or surface rocks are available.
These are constructed in the areas where the depth of soil is shallow. The
cost per ha. comes to Rs 6000-7000/- as on date. The usefulness of the
contour stone wall is to reduce the velocity of run off water; they serve the
purpose of disposing the loose boulders and stones that exist on the fields
and render such areas fit for cultivation.
8. Retaining wall
This type of terrace is formed is areas where soil depth and soil volume
are less and with the available stones and boulders. The construction cost is
cheaper and at the same time pebbles and stones in the field could be utilized
for construction of terrace so that the land is made fit for cultivation. Stream
bank protection by growing vegetation along side and by constructing drains
stone pitching, soil erosion can be reduced.
9. Stream Training Works
Stream Training Works are carried out in streams where they are
meandering and wherever the beds are getting silted up. The work is not
taken up in deep water courses which have already taken a stable position.
144
10 Percolation Tank / Pond
Percolation tanks are constructed across the natural water courses i,e,
nallah to impound the water of streams for a longer time with the objective of '
effective recharge of ground water. Besides, the water table in the wells within
the zone of influence of the pond, get recharged by deep percolation., The
cost comes to Rs 70000 to 1 lakh for one percolation pond.
11. Silt detention Tank
Silt detention Tanks are constructed on the streams in order to prevent
the flow of sediment into the river or dams, Due to construction of silt
detention tanks considerable amount of silt is being detained,. But for the
construction of silt detention tank, the detained silt would have been swept
into the reservoir and dams. The cost per tank comes to Rs, 30,000 to 40,000.
The sediment production rate is expressed in terms of hectare metre per 100
Km2 (ha.m/100 km2). Size of silt detention tank 40m x 20m x 3m.
Erosion control measures
• Gully plugging: construction of permeable check dams.
• Stream bank erosion
• Land slide erosion
• Wind erosion
Moisture conservation works
Biological/Agronomic practice
1. Contour farming
2. Cover crops and legumes
3. Composting
4. Mixed and rotational cropping
5. Green manuring and mulch forming
6. Terracing and dry land farming
7. Agro forestry
8. Dry farming: this practice checks soil erosion where rainfall is low to
moderate.
9. Agrostological methods-soil erosion can be checked by successful growth
of grass which acts as a soil binder.
145
10. Fallowing: Sometimes, it is important to allow much used land to rest or lie
fallow so that natural forces can act on the soil (or for rejuvenation of natural
forces on the soil)
11. Cover cropping: In some cases, as in plantation, where the gestation
period of tree crops is huge, cover crops may be inter planted between the
young trees.
12. Vegetative barrier
Vegetative Barriers
It is suggested to supplement the earthen bunds by vegetative barriers with
vettiver, Agave or with locally growing bushes. Here, the run off will not
stagnate, but the velocity of water will be lowered by the hedges causing
deposition of silt on the upstream side and filtered water, oozing out all along
the barriers. The effectiveness of the vegetative hedges will be less than the
contour bunds with regard to water harvesting and conservation of soil and
moisture. But they are much cheaper than earthen bunds.
Check dams
Checkdams constructed across gullies will serve as an effective water
harvesting structure like mini percolation ponds. Even though their main
purpose is for controlling the development of gullies, series of checkdams
across a gully course will help augment the filling up of water in the existing
wells nearly on both sides of the gully.
Percolation ponds
Percolation ponds are small pods located mostly in low lying areas of
poromboke lands and formed in order to store the run off of rain water and to
allow it to percolate downwards and sideways. Deep ponds are preferred
since evaporation of the stored water there in will be less It has been
observed that the percolation ponds are effective up to a distance of 1 km on
the down stream side and wells within this range are benefited with more
replenishment of water.
Method of Implementing Works
Watershed development work is a 5 year period. The watershed should be
arbitrarily demarked as ridge portion, middle portion and valley portion.
Ridge Portion (1 and 2 years)
-Contour bunding
-Contour trenching
146
-Stone wall check dam
-Planting drought resistant tree saplings
Middle Portion (3rd year)
-Land leveling
-Percolation pond
-Adding silt to the land, planting horticultural tree saplings is a more or less
level land
Valley Portion (4 and 5th year)
-Farm pond
-Percolation pond
-Check dam construction
-Deepening irrigation tanks
-So as to increase the water resources
The comparative severity of erosion and probable sediment yields of different
watersheds.
Determine the erosion Intensity of different watersheds, called as Erosion
Intensity unit, and grade them in accordance with their increasing severity.
Also, find out the probable sediment yield of the watershed and grade them by
order. For grading,the least eroding units are assigned by the number 1 or
0.50, while more eroding units are assigned by higher weights such as 2,3,4.
1. Evaluation and Monitoring
To study the impact of soil conservation measure~ accrued during the
series of years (5 years period)
Crop assessment survey
Crop assessment survey is to be conducted both in ~ills and plains
based on cropping intensity.
Cropping Intensity (Cropping Index)
It is the ratio between total cropped area and actual net cultivated area
expressed in percentage.
Cropping Intensity
= Total cropped area in a year x 100
Net cultivated area
147
it does not take into consideration the length of growing period for
various crops.
- Refers to the raising of a number of crops from the same field during one
agricultural year.
Total cropped area in a year
= 200
Net cultivated area
Cropping Intensity
= 50
= 200 x 100 = 400%
50
One agricultural year comprises of the following 4 seasons:
Dec to Feb. (Winter)
89 days
March to May (Spring)
93 days
June to August (Summer)
93 days
Sept. to Nov. (Autumn)
90 days
Total days in the four season
365 days
2. Tank capacity survey
- is to be conducted to determine the quantity of sediment that is being
trapped and detained in the percolation pond / silt detention tank constructed
the sediment production rate is expressed as in terms of hectare metre per
100 km2 (ha. m/100km2) (1sq. k. = 100 ha; 100 sq. km = 10000 ha)
3. Irrigation potential survey
- is to be conducted for assessing the ground water recharge in the
receiptant wells under the zone of influence of the percolation pond.
4. Soil Loss Minimization survey
To assess how much top soil is retained in the affected area. For this,
select two or more experimental watersheds, which are close proximity or
similar to each other with identical physiography, vegetal covers, soils,
geology and climate. Keep one watershed under control throughout the study
and to other under treatments.
F.A.O. Soil Erosion Classification
EROSION CLASS
ANNUAL SOIL LOSS (T/HA)
None to slight
<10
Moderate ...
10-50
High ...
50-200
Very high ..
> 200
Source: Romeo (1985)
148
Difference between vegetative and mechanical measures
Vegetative Measures
Mechanical measures
1. Provide effect by their product
2. Less costly
3. It is used when mechanical
measures are insufficient
4. Its effectiveness
varies from
season to season.
5.Elevation of degree of control is
difficult
6. Its development take considerable
time before the measures become
effective.
7. It can be developed on wide range
of physical sites
8. It requires little maintenance and
proper management.
1. Not so
2. More costly
3. Rarely used
4. Not so it remain uniform throughout
all the season.
5. Very Easy.
6. It is not so.
7. They can be installed at a suitable
site
8. The management is quite
extensive and expensive
WATERSHED PROBLEM
The problem such as flood, drought, erosion, and sediment damage
and other problem related to conservation development, utilization disposal of
water originating in the watershed, It includes the details on irrigation needs,
drainage, water supply required for agricultural and non agricultural uses and
other management needs.
SPECIAL PROBLEMS
The problem such as: Landslip, landslide, torrents, highway erosion, mines
etc. are counted for preparation of watershed work plan.
PROGRAM FOR SPECIAL PROBLEMS
1. Landslide : Retaining wall or other structures
2. Stream bank erosion : Vegetative or structural methods
3. Erosion along the highway – Vegetation or revetment
4. Gullies and ravines – Vegetation and gully control structures
The benefit likely to be occurred from various means under water/shed
management work are to be evaluated by
• Increased agricultural production.
• Flood control achieved
• Increase of forest produce
• Reduction of sediment load
149
COMPARISON OF BENEFITS AND COST
The comparison of varied benefits obtained and cost incurred is made
by computing the average annual benefit and average annual cost of the
project. The ratio of benefit to cost is computed to show the comparison
between them usually the primary benefits are taken into account for
comparison of benefits and cost of the project.
COST AND BENEFITS
Item
Expenditure
Income
1. Agricultural land.
2. Horticultural.
3. Forest lands.
4. Grassland, pastures and grazing lands.
5. Forest land
6. Special works
___________________________________________________________
Total
____________________________________________________________
Net Benefit; cost benefit ratio ______________________
PHASING OF
MANAGEMENT
THE
PROPOSED
WORKS
UNDER
Programs for special problem
1. Land slide: Retaining wall or other structure.
2. Stream bank erosion: Vegetative or structural method,
3. Erosion along the highway: vegetative or revetment.
4. Gullies and Rivers: Vegetation and gully control structure.
150
WATERSHED
RECOMMENDED MANAGEMENT PROGRAMME
A. Agriculture Land
1. Agronomic practices
2. Engineering measures
• Diversion ditchs
• Bunding
new
• Bench terraces :either renovation of existing terrace or construction of
bench terraces
• Any other structures like parwig grassed waterways, provision of
water harvesting structures, farm ponds, percolation ponds, mulching, contour
furrowing, contour trenching
B. Forest Land
Management of forest according to the density of natural vegetation
1. Engineering measure to be adopted
2. Grassland pastures and grazing land.
3. Farm forestry
4. Orchards
5. Special problems encountered in the recommended management practices
EFFECT OF WORK
Four phases involved in implementing soil water management works .
1. Recognition phase
2. Restoration phase
3. Protection phase
4. Improvement phase
1. Recognition phase
Watershed problems are recognized their probable causes and
development of alternatives for them
2. Restoration phase
Treatment measures are applied to the critical are as for the
recognized problems identified earlier during recognition phase
151
3. Protection phase
General health of watershed is taken care of. The protection of
watershed against all those factors which cause deterioration is also carried
out under this management phase.
d. Improvement phase
The overall improvements made during management of watershed are
evaluated for all the lands covered. In addition, attention is also given to make
improvement on agricultural land, forest land, forage production, pasture land
and socio-economic status of the people.
FORESTRY PRACTICES IN SOIL CONSERVATION
1. Wattling to stabilze debris and landslide
This is one of the improved agronomic practices in hills in combination
with mechanical.
On the hillslopes intensity of erosion by run off water can be reduced
and even controlled by building terraces or benches parallel to or conformable
with the contour lines. Contour terracing and providing reinforcement through
wattling with trees and shrubs planted at suitable intervals of 5 to 7m the
contour terraces are rainforced by wattling of trees and shrubs that sprout
easily. It is the biotechnical method of stabilizing the slopes .
Each of the contour terrace bed is made slightly sloping with levees
(bunds) on the outer margin which would serve as a barrier to run off flow. A
furrow on the inner side would help to drain out excess water and prevent
erosion. As a mater of fact, all bunds and benches are stabilized with
vegetation such as
Tripsacum laxum , Eulaliopsis binata , Ricinus communis etc.
(Tripracum laxum = Gautemala gama grass
Used as fodder and also for paper pulp)
Eulalioposis binata = Baib grats
A perennial tufted grass ,
Used or manufacture of paper ropes, strings and mats
152
Biotechnical method of stabilizing slopes and land slide
1. wattling
2. contour brush layering using willow cutting (salix alba) white willow.
wattle: Frame of woven branches etc, as a fence.
Prepare wattling cigar shaped of live branch with butts tied together
(Thick end)
Log wood check dams
The wooden posts of 8-10 cm dia; 30 cm above the ground level and
75cm below the ground level and 100-115cm apart are erected on the slopes.
153
This will reduce the velocity of water and retain the soil particles. This
becomes one of the temporary checkdams
154
SECTION E - WASTE LAND MANAGEMENT
India is a country with rich natural resources and varied agro-climatic
conditions having different types of land.
Geographical area of the country is 329 million hectares and whole of
the area cannot be put under agricultural use since portion of the area is
under rocks, marshy lands, sloppy lands, rivers, roads, buildings, forests etc ..
and as such only a portion of it can be utilized.
The Ministry of Food and Agriculture has recommended the following
systems of Land use classification.
Land Use Pattern
The total effective area of the country is 304.6 mha.
1. Cultivated area
50% of the total area
2. Forest area
22% of the total area
3. Permanent pasture And
Grazing lands
4% of the total area
4. Fallow lands
8% of the total area
5. Cultivable waste land
6% of the total area (U.P. has the largest
percentage of this category of land)
6. Non-agricultural purposes
like Houses, roads, railways,
industries etc.,
Total
10% of the total area
100%
The fallow lands are kept fallow In order to allow the soil to recover its
fertility. Lands may be kept fallow owing to drought conditions also (8%).
The cultivable wastelands (6%) which were once cultivated, have become
wasteland owing to improper use. Bad drainage, soil erosion, salt
accumulation due to excessive irrigation are some of the causes. These
lands can be reclaimed and used.
The term wasteland has been used as a synonym of land degradation.
According to FAO estimates (1986), about 50% of the total geographical area
in India is under various degradation hazards.
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Water erosion
- 30.3%
Wind erosion
- 16.8%
Salinity
- 2.4%
Total
= 49.5%
Apart from this about 2.1 mha of land is degraded and deforested annually.
Hence urgent measures are to be taken to arrest degradation process so as
to restore productivity of degraded lands.
"The land available for cultivation but not used for cultivation for one
reason or other is called culturable waste land. The cultivable waste
comprises of gullied land, water logged land and marsh, salt affected land,
shifting cultivation area, sandy area, mining and industrial wasteland, pastures
and degraded pastures.
THE NATIONAL WASTELANDS DEVELOPMENT BOARD (NWDB)
It was originally set up in 1985 with the objective of identifying waste
land in non forest area and checking land degradation, putting such waste
lands to sustainable use and increasing biomass specially fuel wood and
fodder.
It is estimated with the work of undertaking the work of afforestation
programme with people’s Participation. Recently the Board was bifurcated to
form, the National Afforestation and Eco-development Board (NAEB) under
the Ministry of Environment and Forests and the Department of wasteland
development which has been transferred to the Ministry of Rural
development. The NAEB is to promote afforestation and Eco-development
with special attention being paid to degraded forest areas, National Parks and
ecologically fragile areas like the western Himalayas, Aravallis and Western
Ghats.
The NWDB is responsible for regeneration and development of waste
lands in non-forest areas aimed at checking land degradation, putting such
waste land to sustainable use and increasing biomass availability, specially
fuel wood and fodder.
Cultivable waste lands
-15mha
Current fallow lands
-20mha
Barren lands
-30mha
(Mountains and deserts)
156
The processes of soil erosion, degradation of watershed areas, deforestation,
desertification not based on the principles of conservation turn arable land into
waste lands. Wastelands suffer from lack of water, water logging, and very
severe soil erosion.
The uncultivable lands include barren lands, rocky areas, steep slopes,
snow covered and glacial areas.
Wastelands Development Programme
Two major objectives :
1.
Identification of nature, extent and locations of wastelands.
2.
Identification of plant species suitable to the wastelands.
The major factors giving rise to wasteland are
a) Indiscriminate deforestation
b) Removal of top soil by water and wind
c) Wrong irrigation practices.
d) Growth of soil salinity.
e), Hooming or shifting cultivation.
f) Degradation of watershed areas.
Judicious management of various resources especially soil resource is the
key to sustain at high productivity, food security and environmental safety.
Management of Wastelands
Wastelands are not difficult to manage. Their reclamation and
development is based on the available soil moisture, soil condition and the
crops to be raised over them. There fore it involves the following 3 major
factors:
1. Water Management
2. Soil Management
3. Crop Management
Types of Wastelands:
To identify a wasteland, one must consider the state of the land at the
present time and its origin.
1. Salt affected lands
2. Ravinous and gullied lands
157
3. Waterlogged or marshy lands
4. Undulating upland with or without scrubs
5. Shifting cultivated area or hooming area
6. Degraded forest land
7. Degraded pastures / grazing land
8. Rocky area
9. Mining / industrial wastelands
10. Steep sloping area
11. Desert land / Arid land
12. Coastal area
Important wastelands Management:
1. Management of degraded pasture land.
2. Management of arid / desert land.
3. Wetland or inundated land Management
4. Management of hilly region
The steps involved in the management will help in improving the
availability of food, fodder and fuel. There is ample scope for utilizing these
areas for afforestation schemes.
1. Management of degraded pasture land or Grassland (Range Land
Management)
A total area of 11 to 12 million hectares is devoted to pasture and other
grazing lands. Grassland soils are rich in organic matter and in mineral
matter, called mollisols. The zonal equivalent of mollisols is the Chernozems.
These soils are associated with Prairie vegetation and have a soft crumb
structure.
E.g.: Prairies of North America also called as World Bread Basket and also as
Never Never Land, Pampas of South America in Central Argentina.
Of the total area, 25% land area constitutes grazing land which
produces fodder just sufficient to meet the requirements of the cattle and
poultry for six months. Overgrazed grassland and forests are subjected to
severe wind and water erosion.
158
Management of Grasslands:
1. Protecting the grassland from biotic interference by means of fencing.
2. Uprooting (grubbing) the unwanted abnoxious weeds like Lantana camera.
Barberies by stump treatment with herbicide 2,4,5, T (Trichlorophenoxy Acetic
Acid) or by spraying with 2% solution of Gramexone.
3. Implementation of soil and water conservation measures:
a). Contour bunding
b). Contour trenching
c). Formation of small brushwood check dams along the gullied range land
4. Land preparation
- By light discing the soil before the onset of monsoon followed by
seeding with appropriate grasses.
5. Sowing grass seeds or planting grass seedlings of herbage quality.
Choice of grass species:
Iseilema laxum - Mushan grass
Perennial grass- used as fodder
Efficient soil binder.
Dicanthium annulatum (Marvel grass)
Cenchrus ciliaris:
(Anjan grass, Bubble grass, African foxtail - Seeds are edible)
Cenchrus setigerusAnjan grass promising grass of the arid zone pasture
Chloris gayana:Rhodes grass, high nutritive value
Panicum maximum:
Guinea grass
Pennisetum puspureum
Napier grass, Elephant grass
Cynadora dactylon :
Bermuda grass, Bahama grass
159
Sorghum sudanense :
Sudan grass
Introduction of legumes like sirato, stylo santhus hamata, desmanthus
In the existing degraded pastures for improving the existing forage quality.
6. Adoption of silvipasture system :( tree-fodder-grassland)
- Raising fuel and fodder plantation in the grassland (a three tier system)
Acacia nilotica - sesbania grandiflora
Laucaena leucocephala, Prosophis juliflora
- may be raised in the grassland.
2. Management of slopy arid region or desert land
The arid regions of India covers an area of 31.7 million ha. Desert
covers about 20% of the total land area. The largest is the Sahara which
covers nearly a third of Africa. Rajastan state alone accounts for 60% of the
arid zone of India. The soil of the order Aridisol -zonal equivalent is sierozem
- arid regions are usually rocky or gravelly with only a small proportion
having covered with sand. Agro forestry practices have been suggested to
better the situation such as sand-dune stabilization, shelter belt plantation,
wind breaks, boundary plantation, silvicultural and agro-silvicultural system.
They could be suitably practised based on situation, purpose and need.
Planting techniques in slopy areas in arid regions:
Planting in sunken pits and triangular (v-shaped) and semi- circular
bunds might improve the survival and growth rates of seedlings over normal
planting pits under these condition due to increased water availability,
reduced wind speed or reduced evapo- transpiration.
160
Ring pit method:
Rain water harvesting structure
Albizzia lebbek and Azadirachta indica can be grown inside the ring pit and
rainwater is stored in the outside pit. This method is experimentally proved
best at Arid Zone Forest Research Institute Jodhpur.
Atriplex lentiformis
Salt tolerant exotic fodder
Atriplex halimus
species
Acacia ampliceps
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Horticultural fruit trees for arid areas:
Aegle marmelos- auspicious tree, medium sized thorny deciduous tree
found in plains and sub mountane regions of India.
Tanarindus indica
Emblica officinalis
Salvadora persica:- mustard tree
species
is indigenous salt tolerant tree
Tamarix aphylla
Tamarix articulate :both are moderate sized trees, suitable for wind break and
shelter belts. Wood is used for agricultural implements and house building.
Tree species
Acacia tortilis
Acacia senegel
Albizzia lebbek
Ailanthus excelsa
Leucaena leucocephala
Eucalyptus termindis
Grass species:
Cenchrus ciliaris
Cenchrus setigerus
Dicanthium annulatum
Panicum antidotale - Bansi grass, Blue panicum
Desert development programme:
The desert development programme (DDP) was started in 1997 -98
both in the hot desert areas of Rajastan, Gujarat and Haryana and the cold
desert rural development areas of Jammu and Kashmir and Himachal
Pradesh and later extended to some districts of Andhra Pradesh and
Karnataka with the aim to combat desertification and restore ecological
balance of the area. The programme envisages an outlay of Rs15 lakhs per
block.
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3. Management of Wetlands (Inundated Lands)
Wetland is any area that is regularly wet or flooded and where the water table
stands at or above the land surface for at least part of the year.
Wetland soils are intrazonal soils- Hydromorphic soils - soil order Inceptisols.
This comes under flood plain soils.
Types of Wetlands:
There are 3 types of wetlands:
1. Moist land- water table is at the surface or below 30-40cm depth
2. Waterlogged- the water table is close to the ground surface and often
flooded during rainy season.
3. Immerged land - ground surface is under water for a considerable time of
the year. The depth of water fluctuates from several cms. In dry season upto
100cm during the flooded period.
Management of Wetlands:
In wetlands, too much water in the soil is the major obstacle to land use
for either forestry or agricultural purposes. Several measures are generally
practiced to improve the site condition.
1. Ditching:
Providing drainage facilities is commonly used to lower the water table
by draining the excess water. The water table is generally controlled below
50cm from the ground surface by providing deep drainage system i.e., wider
and deeper drainage channels.
2. Terracing:
In waterlogged lands, the water table is close to or even above the ground
surface.
The soil removed from the waterlogged and immerged lands is used to raise
terraces on one side and to create ponds on the other side. In immerged land
terraces should be higher and ponds should be bigger and deeper. For
planting trees with a deep root system, terraces should be higher and ponds
should be bigger and deeper. If-fishery is considered as a part of the agro
forestry system, bigger ponds with deeper depths are needed.
Agrosilviaquaculture (Trees + deep rooted plants + floating plants + fishery)
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Recommended Fruit Trees for Wetlands:
1. Jack Fruit- Artocarpus heterophyllus
2. Monkey Jack- Artocarpus lakoocha
Hard wood- house construction work and boat building
Seeds are used as purgative
Fruits are edible
3. Carambola- Averrhoe carambola
Edible fruit substitute for tamarind in cooking
Tolerate waterlogged condition to some extent
Fruits and flowers are fairly good sources of iron and vit. B
Fruits are rich in vit. C
Two varieties occur one with sweet and the other with acidic fruits
Tree Species
Bombax ceiba
Acacia species
Dalbergia sissoo
Dalbergia latifolia
Terminalia arjuna
Salix alba
Sizygium cumini
Eucalyptus robusta
Lagerstroemia species
Taxodium scandens
Water fir
Swamp cypress
Peduncled alder
Pond Cypress
Deciduous conifer
are very popular for
wetland agroforestry
Fodder - Sesbania grandiflora, Glyricidia sepium, Euphorbia species, Agati
sesbania
In shallow ponds, aquatic plants such as rice, lotus can be planted as
crops. Ponds with a water depth more than 1 m are good for breeding fishes.
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Major types of agro-forestry systems
1. Forestry - Agricultural crops ------ Agrosilviculture -- Tree + Grain crop +
Pulse crops
2. Forestry - Agricultural - Animal Husbandry ------- Agrosilvipastoral - Tree +
Forage + Vegetable crops
3. Forestry - Agricultural - Fishery ---- Agrosilviaquaculture - Trees + Deep
rooted plants + Floating plants + Fishery (Rohu, Catla)
4. Forestry - Agricultural - Fishery - Animal
Agrosilviaquapastoral- Trees + Crops + Fodder + Fishery
Husbandry
-
Shallow water logged areas used by planting water loving plants (Lotus, Rice)
or trees which are deep rooted.
In deep water logged areas, lift pump may be used for drainage and
after drainage, ridges of 60 cm height and 50 cm width at the top are formed,
trees are planted in the mid of these ridges or in the mounds of 30 to 60 cm
height. Once the trees have established, water logging can be reduced.
Syzyzium cumini (Jamun) is the best suited to these areas.
Tollarent tree species: Syzyziium cumini, Eucalyptus robusta,
Lagerstroemia species (ornamental tree), Terminalia arjuna and Salix alba
(small tree)
Deep water logged areas are not possible to be reclaimed.
4. Management of Hilly Region
A hill region is defined as an area with a natural elevation up to a
certain height on the earth's surface. This region is characterized by climatic
and edaphic variations, depending on where it is located and its elevation.
The degree of slope and the quality of soil varies from place to place. On hill
tops, the soils are shallow and poor, whereas in the lower aspects it is deep
and fertile.
In bare hilly region soils are severely weathered, contain only little
organic matter and have a very little capacity for moisture and nutrients. In
addition, they are prone to serious erosion hazards if not managed carefully.
Hilly forest soils are of the soil order - Spodosol .
Zonal equivalent is Podzol. These are the soils developed under humid
coniferous conditions, with accumulated organic matter plus iron and
Aluminium oxides.
Dense forest soils with high content of organic matter is Histosol.
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The practice of Agro-forestry suits best in a hilly region and may work
as an universal remedy to the problem of soil erosion and water loss of this
region. Hill forest is also called as Montane Forest.
Hill Agro-forestry
1. Silvihorticultural System (Forest trees + Horticulture plants)
Depending on the situation, and agro-climatic condition, horticultural
crops must be suitably combined with forest tree species for fodder, fuel and
fishes.
Suitable combinations:
Plantation crop: Cardamum, tea, rubber and coconut.
Coconut - Cocos nucifera (Hindi Nariyal)
Cardomum - Elittiera cardamomum - Used as spice and flavouring material.
Tea – Camelia japonica - Two types Black tea and Green Tea
Black tea - Leaves withered, rolled, fermented and dried.
Green tea - Leaves steamed and dried without fermenting it.
Rubber - Hevea brasilensis - Para rubber (Euphorbiaceae)
Medicinal Plants: Solanum khasianum, Dioscorea prazeri - Tubers are
sources of Cartisone which is used in rheumatism and ophthalmic disorders.
Rhizomes are also used as substitute for soap for washing hair.
Rauvolfia serpentina (Serpentine root) - Drug Rauvolfia consists of air
dried roots. Rauvolfia preparations are used as antihypertensive and as
sedatives. Also employed for relief of various central nervous system
disorders associated with epilepsy. Extracts of roots are valued for treatment
of intestinal disorders. Juice of leaves is used as remedy for opacity of
cornea.
Food and oil producing trees - Madhuca indica
Sericulture: Morus alba
Flower crops: Orchids Ex. Vanda
Fruit trees: Orange, Apple, Pea, Peach
Spice crops: Turmeric (Curcume domestica) and Ginger (Zingiber
officinalis) along with suitable forest trees. Rhizomes are used as spice and
condiment.
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Used in medicine as digestive stimulant. Essential oil from rhizomes used for
flavoring purposes.
2. Silvipasture System: Forest trees in association with grassland.
Ex. Albizzia lebbek with natural grass.
3. Agrosilviculture system
Field crops viz. wheat, maize, bean, tomato, potato, mustard, pea,
cauliflower, pepper, chillies etc. are cultivated in new plantations until the
trees do not affect production due to shading.
4. Agrihorticulture system
Horticultural crops viz, apple, peach, plum, apricot, cherry, almond etc
in between trees, cash crops viz, cabbage, tomato, cauliflower, chilli, bean,
ginger etc. may be grown. Among cereal crops wheat and maize are
common. Such systems are chiefly profitable for smaller holdings.
Important tree species suitable for Agro-forestry in hilly region of India
Albizzia chinensis, Alnus nitida (Himalayan Black Cedar), Ailanthus
excelsa, Cedrus deodar, Eucalyptus grandis, Leucaena leucocephala, Acacia
auriculiformis, Bombax ceiba, Eugenia jambulana (Syzizium cumni), Erithrina
indica, Sesbania bispinosa.
It can be concluded that the practice of Agro-forestry suits best in a hilly
region.
Plantation techniques in problem soils
1. Saline soils
Occur due to deposition of neutral soluble salts like CaCl2, CaSO4,
MgCl2 and MgSO4. Its electrical conductivity > 4 dsm-1 which is a measure of
its salt content measured by EC meter. pH is less than 8.5.
This occurs in treeless forest area or trees are sparsely prevalent i.e.
soil is exposed to atmosphere.
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Plantation techniques in saline soils
1. Pits of size30cmx30cmx120cm(length) are dug in patches of good soil. If
such good patches are not available, the pits may be dug out and filled with
the soil mix viz., red earth or tank silt+ gypsum+FYM (6:2:2) in the pit to have
good initial growth.
The level at filled soil should be 10cm above the adjacent bad soil in
sloppy way,sloping from the centre. Tree saplings should be planted at the
centre. This will avoid accumulation of water nearer to the plant.
2. Boat pits of 30-45cm wide with the trough like bottom (10 cm depth) are
dug to retain the maximum rain water.
Planting is done at the centre of the trough with some imported good soil.
3.Cube pits of size 1.2mx1.2mx1.2m are dug,filled with soil mix i.e red earth
or tank silt+ gypsum+FYM (6:2:2) to half pit in a slopy way,,sloping from the
centre and planted at the centre with tree seedlings like Dalbergia
sissoo,Albizzia lebbeck or Albizzia procera.
Watered with good water or rainwater. This technique is adopted in Uttar
Pradesh has given good results. For reclaimation of saline soils, biological
approach i.e raising of forest trees has been followed by many workers.
Salinity tolerant tree species (Aburol and Dhruvanarayan)
Prosopsis chilensis
Prosopsis cineraria
Acacia auriculifornis
Acacia tortilis -pods for cattle feed - tree withstand drought and frost
A. nilotica
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A. catechu
A. senegal
Casuarina obesa
Casuarina equisetifolia
Eucalyptus umbellata
Pongamia pinnata
Terminalia arjuna
Terminalia aphylla
Lucaena leucocephila
2. Alkali Soil
•
Characterised by the presence of Na2CO3 and NaHCO3 which undergo
alkaline hydrolysis producing NaOH in which Na+ is the dominant cation.
Na2CO3 +2HOH --> 2NaOH+H2CO3
In this soil ESP is 15%, pH 8.5-10, Ec < 4dsm-1
Reclaimation is done by the application of gypsum -but this is highly
impracticable
in forest area.
Plantation techniques
In the alkali forest area, pits of size 1’ x1’ x2’ (d) are dug in patches of
good soil. In case no such patches occur, the sides of the pit are filled with
soil mix i.e , red earth or tank silt + gypsum + FYM (6:2:2) to provide a
favourable medium for initial growth during the establishment period for the
moderately alkaline soil of pH 8-9.
In case of highly alkaline soil of pH >9 , the soil mix is completely filled
in the pitt and the level of soil mix is raised 8-10cm higher than the surface
sloping from the centre to the sides.
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Tolerant tree species
Azadirachta indica
Pongamia pinnata
Prosopsis sp
Acacia sp
Casuarina sp
Eucalyptus sp
Tamarindus indica
Moringa oleifera
Pithecollobium dulce
Albizzia lebbek
Mulberry – Moris alba
Sesbania grandiflora
Ailanthus excelsa
Terminalia arjuna
In the interspace of tree seedlings, dryland food crops like sorghum, maize,
cumbu or napier grass may be grown.
3. Saline Alkaline soils
The problem is two fold
a) high salt content (salinity)
b) presence of hard pan of Na+ clay (alkalinity) ph-8.5-10.0
pH 8.50 – 10.0
EC > 4 dsm-1
ESP >15%
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Plantation techniques
In the saline alkaline forest area, pits of size 1’x1’x2’(d) are dug .The
sides of the pit are filled with soil mix paste i.e , red earth or tank silt+
gypsum+FYM (6:2:2) and the mix is filled in the pit upto half the height of the
pit in a slopy way, sloping from the centre. Tree saplings should be planted at
the centre. This will avoid accumulation of water nearer to the plant.
Tolerant tree species
Acacia sp
Casuarina sp
Ailanthus sp.
Albizzia sp.
Azadirachta indica
Sesbania sp
Tamarindus indica
Tamarix sp
In the interspace of tree seedlings, the following tolerant grass species
can be raised.
Cynodon dactylon- Bermuda grass-perennial fodder crop- used for
tennis lawns
Pennisetum purpureum- Hybrid Napier, Elephant grass-used as fodder
Pannicum maximum-Guinea grass-fodder
Chloris gayana-Rhodes grass-perennial high nutrit/.we fodder
4. Waterlogged soils (pH 6.0-8.0)
When the inflow/influx water (I) viz.,rainfall and applied irrigation water into the
ground water exceeds the outflow (Q) (expenditure i.e, in the form of
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evaporation, infiltration and run off) I it results in the rise of water table and
waterlogging or inundation occurs.
Further it occurs when there are no drainage facilities. The main disadvantage
of this soil is that the plants whither for worst of soil air. The plants and soil
microorganisms cannot respire, with the result the plant wilts.
Plantation techniques
Select tree species that withstand waterlogging. Planting is done in ridges and
soil mounds accompanied with drainage system;--system successfully done
at Punjab.
Tall plants at 2m or 3m height may be planted on mounds of suitable
dimensions so that they can escape complete submergence during rainy
season.
Planting may be done in February and they may be watered in summer
so that the seedlings would be established well during rainy season. Drainage
can be done wherever necessary. Afterwards even if waterlogging occurs, no
damage will be caused to the planted seedlings.
Tolerant tree species
Bombax ceiba
Acacia sp
Terminalia arjuna
Dalbergia sissoo
Dalbergia latifolia
Salix alba
5. Mine Spoils
During surface mining, the surface soil and underlying geologic
structure are opened and deepened for the exploitation of natural resources
like coal, copper, iron, limestone, rock phosphate, bauxite etc. during which
process large quantities of soil have to be taken by heavy machineries.
The excavated soil during mining operations is called mine spoils.
Surface mine waste areas are called spoil banks.
The excavated soil has to be leveled by machineries and the
underlying materials viz. stones, boulders etc. are deposited on the surface.
The final surface after being disturbed may vary in slope, texture, structure,
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fertility and available soil water for plant growth and the soil is subjected to
water and wind erosion.
The first of surface mining involves the removal of vegetation and top
soil.
Much of the mining activity in India is being carried out in forested
regime which results in destruction and erosion.
Mine spoil reclamation process of mine dump areas (spoil banks)
Reclaiming or revegetating mine and construction sites is a costly
effort.
Before mining, the top soil is to be removed and conserved in a
separate location, protected from contamination by strongly acidic/alkaline or
others toxic spoils and seeded(planted) with appropriate fast growing plants to
inhibit water and wind erosion(especially grass species)
After the spoil materials are finally removed and dumped and levelled
by machinery(bulldozer), the protected top soil is be spread uniformly over all
the surface up to 30cm depth. If sufficient top soil is not available, sub soil that
will support plant growth may be used.
The new soil surface may be saline or alkaline or saline alkaline. Here
the forestry measures of managing the problem soils like pitting, application of
soil mix are to be adopted.
If the new area shows a pH more than 8.5, the following tree spp. may
be raised.
Leucaena leucocephala - Subabul
Leguminous trees such as
Dalbergia sisso
Albizia lebbek,
A. procera
Acacia auriculiformis
Acacia mellifera
Casurina equisetifolia
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Mine Dump Afforestation:
1. Suitable tree spp. for coal mine areas (alkaline)
Acacia auriculiformis
Dalbegia sissoo
Pongamian pinnata
Pithecellobium dulce
Cassia siamea
2. Suitable tree spp. for copper mined areas(alkaline)
Albizia procera
Dalbergia sisso
Eucalyptus citriodora
Gemelina arborea
3. Suitable tree spp. for rock phosphate mined areas(acidic)
Acacia catechu,
Dalbergia sissoo
Albizzia lebbek,
Leucaena leucocephala
4. Suitable tree spp. for Lime stone mined areas(acidic)
Azadirachta indica,
pithecellobium dulce,
Pennisetum purpureum
Woodfordia fruticosa
Agave spp.,
Vitex negundo
Shrubs and Grasses
Vitex negundo,
Agave sialana,
lpomea carnea,
Pennisetum purpureum
Rumex hestatus
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Saccharum spontaneum
Mimosa hemata
M. pudica
Tolerant spp. common for all mines areas.
Dalbergia sissoo
Eucalyptus sp.
Acacia sp.
Neem
Albizzia sp.
Casuarina sp.
Pithecellobium dulce
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