Soil Sciences
Student’s Book
FET FIRST
Level 3
J de Fontaine and F Mitchell
FET FIRST Soil Sciences NQF Level 3 Student’s Book
© J de Fontaine and F Mitchell 2007
© Illustrations and design Macmillan South Africa (Pty) Ltd 2007
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First published 2008
08 10 09 07
1 3 5 7 9 10 8 6 4 2 0
Published by
Macmillan South Africa (Pty) Ltd
Private Bag X19
2096 Northlands, 2116
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South Africa
Text design by Heather Brooksbank
Cover design by Deevine Design
Artwork by Mark de Lange and Ian Greenop
Typesetting by Future Pre-Press
Edited by Tony Lavine and Peta Jones
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ISBN-13: 978 085320 892 1; eISBN: 97 8143102 067 6
WIP: 1972 M000
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without written permission from the publishers.
The publisher would like to thank the following for permission to
use photographs in this book:
Science Photo Library: pages 9, 87, 172
The Bigger Picture: page 151
Contents
Topic 1: Fertilisation of soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Module 1: Essential plant nutrients in fertilisers and the principle of limiting factors
Unit 1:
Unit 2:
Unit 3:
Unit 4:
Essential plant nutrients . . . . . . . . . . . . . .
The principle of limiting factors . . . . . . . . . .
Symptoms of nutrient deficiencies in crops . . .
Mixed fertilisers and their application . . . . . .
Module 2: Organic and inorganic fertilisers
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. . 3
. . 9
. 14
. 21
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Unit 1: Using organic fertilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit 2: Green manures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit 3: Advantages and disadvantages of organic and inorganic fertilisers . . . . . . . . . . . . . . . . . . . . . .
29
44
50
Module 3: Problem soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Unit 1: Acidic, alkaline and sodic soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit 2: Soil pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit 3: Management of problem soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
67
74
Module 4: Using soil and plant analysis to determine fertiliser requirements . . . . . . . . 80
Unit 1: Soil and plant sampling for analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit 2: Calculation of fertiliser requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Topic 2: Soil water and evapotranspiration
81
93
. . . . . . . . . . . . . . . . . . . 109
Module 1: Soil water and the process of evapotranspiration
. . . . . . . . . . . . . . . . . 110
Unit 1: Soil water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Unit 2: Evapotranspiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Module 2: Calculating irrigation requirements
. . . . . . . . . . . . . . . . . . . . . . . . . 133
Unit 1: Irrigation requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Topic 3: Soil erosion and its prevention
. . . . . . . . . . . . . . . . . . . . . 151
Module 1: Causes, forms and consequences of erosion
. . . . . . . . . . . . . . . . . . . . 152
Unit 1: Causes and forms of soil erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Unit 2: Indicators and impacts of soil erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Module 2: Prevention of soil erosion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Unit 1: Preventative measures for soil erosion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
Topic 1
Fertilisation of soils
Overview
In this topic you will …
• identify the essential plant nutrients in fertilisers
• understand the principle of limiting factors
• describe the use of organic and inorganic fertilisers
• identify problem soils
• learn to use soil analysis to determine fertiliser requirements.
1
Module 1
Essential plant nutrients
in fertilisers and the
principle of limiting
factors
Overview
In this module you will …
• list the available sources of macro- and micro-nutrients
• explain the principle of limiting factors
• describe deficiency symptoms in crop plants
• explain the concept of mixed fertilisers and describe methods
of applying solid fertilisers.
2
Topic 1: Module 1
Unit 1: Essential plant nutrients
Introduction
In this unit you will learn about the nutrients that plants need in
order to grow, develop and reproduce in a healthy way. You will learn
about essential and non-essential plant nutrients and macro- and
micro-nutrients. The unit deals with the sources and functions of each
macro- and micro-nutrient.
Plant nutrients
Plants need nutrients in order to grow, develop and reproduce. Plant
nutrients are chemical elements such as carbon (C) and nitrogen (N).
Plant nutrients are sometimes called ‘plant elements’.
Plants get carbon (C), hydrogen (H) and oxygen (O) from the air and
water. However, plants get all of their other nutrients from the soil.
In the soil, plant nutrients occur in the form of mineral salts. Mineral
salts are inorganic ions that form when rock particles are broken
down by the process of weathering. The mineral salts dissolve in the
water in the soil. Plants are then able to absorb the mineral salts, and
the nutrients they contain through their roots.
Plant nutrients can be divided into two main categories:
• essential nutrients – nutrients that plants must have in order to
grow, develop and reproduce
• non-essential nutrients – nutrients that plants do not need in order
to grow, develop and reproduce, but which are still needed for
special functions in the plant
In order to be healthy, plants need all of the essential plant nutrients.
In addition, plants need the correct amount of each essential nutrient.
We divide essential nutrients into two types based on the amount of
the nutrient needed by plants:
• macro-nutrients – essential nutrients that are needed in large
amounts by plants
• micro-nutrients – essential nutrients that are needed in small
amounts by plants
Words &
Terms
chemical
ele
substance ments – pure
s made up
of only
one kind o
f atom
mineral s
alts – com
pounds
occurring
in rocks o
r soil
and made
up
negative io of positive and
ns
inorganic
ions – cha
rged ions
of minera
l origin
weatherin
g – chang
es
and soil d
ue to expo in rock
sure to th
weather
e
absorb –
take in or
swallow u
p
??
?
Did you know?
‘Macro’ means ‘large’. Macronutrients are called macronutrients not because they are
large in size but because they
are needed in large amounts.
‘Micro’ means ‘small’. Micronutrients are called micronutrients not because they are
small in size but because they
are needed in small amounts.
You will learn more about macro- and micro-nutrients in the next two
sections.
To make sure that a crop is healthy and gives a good yield, the farmer
must check that the crop has each of the essential plant nutrients in
the correct amounts.
Macronutrients
You have learnt that macro-nutrients are plant nutrients that plants
need in large amounts. Let us look in more detail at the sources and
functions of the different macro-nutrients.
Unit 1: Essential plant nutrients
3
Carbon (C), hydrogen (H) and oxygen (O)
Of all the macro-nutrients, carbon, hydrogen and oxygen are needed
in the largest amounts by plants. Plants get carbon mainly from the
carbon dioxide gas (CO2) in the air. Plants get hydrogen and oxygen
mainly from water (H2O) in the soil.
Functions of carbon, hydrogen and oxygen
• Carbon, hydrogen and oxygen are used by plants to make the large
organic molecules such as carbohydrates and lipids that make up
the structure of the plant and supply energy.
Carbon, hydrogen and oxygen are the only macro-nutrients that
plants get from the air or water. Plants must absorb the rest of the
macro-nutrients from the soil.
Nitrogen (N)
Nitrogen is the macro-nutrient that most affects plant growth and
therefore crop yield.
Functions of Nitrogen
• Nitrogen is needed for the growth of stems and leaves. This is
called vegetative growth.
• Nitrogen is also needed to make proteins, enzymes and the
pigment chlorophyll, needed for photosynthesis.
• There is usually a lot of nitrogen in soils. However most of the
nitrogen in soils is in the form of organic nitrogen in the organic
matter in the soil. Plants cannot absorb nutrients if they are in
an organic form. Plants can only absorb nutrients in the form of
inorganic ions. The inorganic sources of nitrogen in the soil that
plants can absorb are ammonium ions (NH4+) and nitrate ions
(NO3-). Bacteria in the soil gradually change organic nitrogen into
the inorganic ammonium and nitrate ions that plants can use by a
process called mineralisation.
Phosphorus (P)
The main source of phosphorus in the soil is in the form of phosphate
ions (PO43-). The availability of phosphorus from the soil is strongly
dependent on the pH or acidity of the soil. At a pH lower than 5.5,
the phosphorus in the soil tends to react with iron (Fe) in the soil to
form a compound that cannot dissolve in water and therefore cannot
be absorbed by plants. At a pH above 6.0, this reaction is reversed
and the phosphorus becomes available for plants to absorb. The best
soil pH in terms of phosphorus availability is between 6.0 and 7.0.
Phosphorus availability can also be influenced by other inorganic ions
in the soil. For example, phosphorus combined with aluminium or
iron cannot be absorbed by plants, but phosphorus combined with
calcium or magnesium can be absorbed by plants.
Functions of Phosphorus
• Phosphorus is needed for root growth and the formation of the
reproductive parts of the plant, such as flowers, fruits and seeds.
• Phosphorus is also needed to make cell membranes, enzymes,
nucleic acids (the carriers of genetic information) and energycarrying molecules.
4
Topic 1: Module 1
Words &
Terms
organic –
living or d
ead part o
an anima
f
l or plant,
containing
carbon in
its molecu
les
carbohyd
rate – ene
rgyproducing
organic co
mpounds
of carbon
(C), hydro
gen (H)
and oxyge
n (O) e.g.
sugars an
starch
d
lipids – fa
ts
proteins –
a group o
f organic
compound
s containin
g carbon,
hydrogen
, oxygen,
nitrogen (N
and some
)
tim
phosphoru es sulphur (S) and
s (P)
enzyme –
a compou
nd that
facilitates
or speeds
up
chemical
reactions
changes
mineralis
ation – ch
ang
organic su
bstance in ing an
to a nonorganic su
bstance
Potassium (K)
The source of potassium in the soil is the potassium ion (K+).
Functions of potassium
• Potassium has many functions, but is very important for fruit
development.
• It is also needed for regulating water absorption and
• for promoting resistance to diseases and difficult environmental
conditions like frost and drought.
Magnesium (Mg)
Magnesium is absorbed in the form of magnesium ions (Mg2+) from
the soil.
Functions of magnesium
• Magnesium is needed to make chlorophyll and for getting enzymes
to work.
Calcium (Ca)
Calcium is absorbed in the form of calcium (Ca2+) ions.
Functions of calcium
• Calcium is needed for the growth of the tips of roots and stems
• storage of food
• pollen formation and to prevent leaves from falling off the plant
too soon.
• for the structure and functioning of cell walls and cell membranes.
Sulphur (S)
Sulphur is absorbed in the form of sulphate ions (SO42-) from the soil.
Functions of sulphur
• Sulphur is needed for the formation of certain important proteins
and enzymes.
Assessment activity 1
Summarising the function of macro-nutrients in the plant
1. Use the information in the text to complete the following table for summarising the function of
macro-nutrients in plants.
Table 1: The sources and functions of plant macro-nutrients
Macro-nutrient
Symbol
Carbon
C
Sources
Function in the plant
Hydrogen
Oxygen
Nitrogen
Phosphorus
PO43-(phosphate ion in the soil)
Potassium
Unit 1: Essential plant nutrients
5
Magnesium
Formation of chlorophyll;
functioning of enzymes
Calcium
Sulphur
Micro-nutrients
Unlike macro-nutrients, micro-nutrients are needed in very small
amounts. Micro-nutrients are sometimes called trace elements because
plants only need trace amounts of them. However, just because micronutrients are needed in small amounts they are not less important than
macro-nutrients. Micro-nutrients are essential nutrients and plants
cannot survive without them.
Words &
Terms
trace – ve
ry
small qua
ntity
Micro-nutrients including iron (Fe), manganese (Mn), copper (Cu),
boron (B), zinc (Zn), cobalt (Co), molybdenum (Mo), sodium (Na) and
chlorine (Cl) are essential to some plants too. Most micro-nutrients are
involved in the functioning of enzymes in the plant. We still do not
know exactly all of the functions of each micro-nutrient. Table 2 shows
the sources of micro-nutrients in the soil and the known functions of
each micro-nutrient.
TABLE 2: The sources and functions of plant micro-nutrients found in the soil
Micro-nutrient
Source
Function
Iron (Fe)
Fe2+ (ferrous ions);
Fe3+ (ferric ions)
Formation of chlorophyll; functioning of enzymes
Manganese (Mn)
Mn2+ (manganese ions)
Functioning of enzymes
Copper (Cu)
Cu2+ (copper ions)
Functioning of enzymes
Boron (B)
BO3- and B4O72- (borate ions)
Absorption of calcium; growth of shoot tips
Zinc (Zn)
Zn2+ (zinc ions)
Formation of plant hormones; functioning of enzymes
Cobalt (Co)
Cu2+ (copper ions)
Functioning of enzymes
Molybdenum (Mo)
MoO42- (molybdenum oxide
ions)
Functioning of enzymes needed for nitrogen based
reactions
Sodium (Na)
Na+ (sodium ions)
Regulation of osmosis and the maintenance of salt
water balance
Chlorine (Cl)
Cl- (chloride ions)
Regulation of osmosis and the maintenance of salt
water balance
6
Topic 1: Module 1
Case Study 1
Hydroponics
Hydroponics is a method of growing plants without soil. The plants are grown in stable growth media, such as
gravel or sawdust. The nutrients the plants need are dissolved in distilled water to form a nutrient solution.
The nutrient solution is supplied to the plants as irrigation at regular intervals. High value crops are suited to
hydroponic production to offset the high cost of this production system. In South Africa, tomatoes, cucumbers,
peppers, lettuce and herbs are popular choices for hydroponic production.
Tomatoes are usually grown in a ‘drain to waste’ or ‘open bag’ hydroponic system. In this system, plants are
grown in open containers. The nutrient solution is supplied about 12 times a day by means of a dripper. Excess
nutrient solution drains out of the containers as waste.
Herbs are often grown in a gravel-flow hydroponic system. In this system, the nutrient solution is re-circulated
so that the roots of the plants are covered in a thin film of the nutrient solution at all times.
There are many types of nutrient solutions that can be used for hydroponics. One of the more commonly used
solutions is called a modified Hoagland solution.
Assessment activity 2
Case study on hydroponics
1. Read the case study on hydroponics on the previous page.
2. Table 3 shows the components of a modified Hoagland nutrient solution commonly used in
hydroponic systems. Complete the table by determining which nutrients are supplied by each
component.
TABLE 3: Sources of nutrients in a modified Hoagland solution
Component of solution
Chemical formula
Source of which nutrient/s?
Ammonium phosphate
NH4H2PO4
Nitrogen, phosphorus
Potassium nitrate
KNO3
Calcium nitrate
Ca(NO3)2
Magnesium sulphate
MgSO4
Iron phosphate
FePO4
Boric acid
B(OH)3
Manganese chloride
MnCl2
Copper chloride
CuCl2
Zinc chloride
ZnCl2
Molybdenum oxide
MoO3
Ammonium molybdenum oxide
(NH4)6Mo7O24
Manganese, chlorine
3. List the macro-nutrients and micro-nutrients available in a modified Hoagland solution.
Unit 1: Essential plant nutrients
7
Assessment activity 3
Short test on macro- and micro-nutrients
1. Define the following terms:
a) plant nutrients
b) essential plant nutrients
c) macro-nutrients
d) micro-nutrients.
2. Are macro-nutrients more or less important than micro-nutrients for plants? Explain.
3. Complete the following table:
Macronutrient
Source
Function
nitrogen (N)
phosphorus (P)
potassium (K)
4. Why is magnesium important for plants?
5. Which two micro-nutrients are needed for a plant to maintain its salt water balance?
Assess yourself
Assess your performance in the following activities:
1
2
3
4
Summarising the function of macro-nutrients in the plant
Case study on hydroponics
Short test on macro- and micro-nutrients
1 = not achieved; 2 = not yet competent; 3 = competent; 4 = outstanding
Unit summary
This unit deals with the nutrients that plants need for healthy growth, development and
reproduction. Plant nutrients that are needed for plants to survive are called essential plant
nutrients. Essential plant nutrients are classified as macro-nutrients or micro-nutrients. Macronutrients (C, H, O, N, P, K, Mg, Ca and S) are those nutrients that are needed in large amounts
by plants. Micro-nutrients (Fe, Mn, Cu, B, Zn, Co, Mo, Na and Cl) are those that are needed in
small amounts by plants. The unit deals with the sources and functions of each macro- and micronutrient.
8
Topic 1: Module 1
Unit 2: The principle of limiting
factors
Words &
Terms
principle
Introduction
This unit deals with a very important idea. It is the idea or principle
of limiting factors. The unit covers the basic concepts behind the
principle of limiting factors. The emphasis is on the role of plant
nutrients as limiting factors.
organism
– general
law
– any livin
g thing
Every organism needs certain things in order for it to survive. For
example, the basic things that plants need include sunlight, carbon
dioxide, water, nutrients, a growth medium like soil, and a favourable
temperature and pH.
If an organism does not have enough of any one of these factors,
the organism will struggle to survive, even if all the other things are
present in the right amounts. For example, a plant may have the right
amounts of sunlight, carbon dioxide, nutrients, soil, and a favourable
temperature and pH, but if it does not have the right amount of water,
it cannot survive. In this case, water is the limiting factor. Water is
limiting the survival of the plant.
The Principle of Limiting Factors states:
• “The functioning of an organism is limited by the essential
environmental factor that is present in the least favourable
amount”.
Figure 1.1: Tomatoes being grown under hydroponic conditions. The hydroponic
system provides everything the plant needs in optimum amounts. As a result,
limiting factors never affect plant growth
Unit 2: The principle of limiting factors
9
Liebig’s Law of the Minimum
The Principle of Limiting Factors developed from a law in agricultural
science called Liebig’s Law of the Minimum. Liebig’s Law of the
Minimum was formulated in 1840 by a German scientist called Justus
von Liebig.
Liebig’s Law of the Minimum states:
• “Growth is controlled not by the total of resources available, but by
the scarcest resource.”
Liebig’s Law was originally developed from crop growth studies. It is
based on the observation that adding more of the plant nutrients that
were already present in high amounts did not lead to an increase in
plant growth. Plant growth only increased when more was added of
the plant nutrient that was present in the lowest amount.
Assessment activity 1
Liebig’s barrel
Liebig used a barrel to explain his Law of the Minimum. Imagine a barrel made with pieces of
wood that are different lengths. Each piece of wood represents one essential nutrient that a plant
needs to grow. The length of wood represents the amount of nutrient available. The volume of
water the barrel can hold is limited by the shortest piece of wood. In the same way, the growth of a
plant is limited by the nutrient that is in shortest supply.
Figure 1.2: Liebig’s barrel illustrating his Law of the Minimum
1. In a group, suggest other ways that you could demonstrate Liebig’s Law of the Minimum.
2. Choose one suggestion and present it to the class.
10
Topic 1: Module 1
Tolerance limits
Liebig’s Law of the Minimum only dealt with limiting factors as those
factors that were present in too little amounts. However, too much of
a factor can also limit an organism’s survival. For example, too much
heat can kill a plant. Too much water can drown a plant. Too much of
a certain plant nutrient can become toxic for a plant.
This brings us to the idea of tolerance limits. Each organism has an
optimal range for each environmental factor within which the growth
and development of the organism is optimal or best. For example,
each crop has an optimal range for the level of nitrogen in the soil
(Figure 1.3). In the optimal range, the crop plants show the best
growth. There are minimum and maximum values called ‘optimal
limits’ that define the lower and upper values of the optimal range.
Below the lower optimal limit, the crop will have a deficiency of the
nutrient. The crop will become stressed. It will show symptoms of
deficiency and its growth will decrease. Eventually there is a limit of
tolerance beyond which the crop cannot survive and growth drops to
zero. Above the upper optimal limit, the nutrient level is so high that
it becomes toxic to the crop. The crop becomes stressed. It shows signs
of toxicity and its growth decreases. Above the maximum limit of
tolerance, the crop cannot survive and growth drops to zero.
deficient
sufficient
toxic
Figure 1.3: Graph showing a certain crop’s range of nitrogen tolerance
Unit 2: The principle of limiting factors
11
Assessment activity 2
Interpretation of graphs of tolerance
Study the graph in Figure 1.3 and answer the following questions:
1. What is the optimal range of nitrogen for this crop?
2. What is the upper limit of tolerance?
3. What is the lower limit of tolerance?
4. What is the lower optimal limit?
5. What is the upper optimal limit?
6. What is the maximum growth that the crop is capable of, and what is the nitrogen value at this
point?
7. At a nitrogen level between 4 ppm and 8 ppm, what happens to the growth of the crop plants?
Why does this happen?
8. At a nitrogen level between 19 ppm and 23 ppm, what happens to the growth of the crop plants?
Why does this happen?
9. Why does the growth of the crop reach zero below 4 ppm nitrogen and above 23 ppm nitrogen?
Conditions affecting limiting factors
There are various things that can affect the limiting factor in a field at
a certain time and place. These include:
Seasonality
Limiting factors can be seasonal. In other words, an environmental
factor may be the limiting factor at a certain time of the year but not
at other times of the year. For example, in winter, temperature may
become the factor limiting growth. But in the warmer months of
spring and summer, the temperature is no longer the limiting factor
and other factors like water or nutrients may become the limiting
factor. Water is a seasonal factor because rainfall varies from month to
month. Light is seasonal because day length and light intensity varies
from season to season.
Type of crop
Different crops and cultivars have different nutrient requirements.
This is because they have different growth rates, root structures,
and efficiencies of nutrient use. As a result, in one field, plants from
Crop A will be use up one factor faster than plants from Crop B. The
nutrient becomes the limiting factor for Crop A but not for Crop B.
Growth stage of crop
Limiting factors may also change depending on the growth stage of
the crop. Crops have different nutrient requirements at different stages
of their life cycle.
12
Topic 1: Module 1
Assessment activity 3
Short test on limiting factors
1. Write the Principle of Limiting Factors in your own words.
2. State Liebig’s Law of the Minimum.
3. What do the following terms related to tolerance limits mean?
(a) optimal range
(b) upper optimal limit
c) lower limit of tolerance.
Assess yourself
Assess your performance in the following activities:
1
2
3
4
Liebig’s barrel
Interpretation of graphs of tolerance
Short test on limiting factors
1 = not achieved; 2 = not yet competent; 3 = competent; 4 = outstanding
Unit summary
This unit deals with the concept of limiting factors. The Principle of Limiting Factors states that
the functioning of an organism is limited by the essential environmental factor that is present in
the least favourable amount. This principle, developed from Liebig’s Law of the Mimimum, states
that growth is controlled not by the total of resources available, but by the scarcest resource. Each
organism has upper and lower tolerance limits for each limiting factor.
Unit 2: The principle of limiting factors
13
Unit 3: Symptoms of nutrient
deficiencies and toxicity in
crops
Introduction
In this unit, you will learn about the different symptoms or signs that
indicate that a plant is deficient in one or more plant nutrient. If a
plant does not have enough of a particular nutrient, the plant usually
shows certain symptoms. Symptoms can be a change in the colour or
shape of the plant’s leaves. If a farmer knows and can recognise such
nutrient deficiency symptoms, then the nutrient that is in short supply
can be increased by the application of the appropriate fertiliser.
The use and limitations of nutrient
deficiency symptoms
Nutrient deficiency symptoms which can be seen with the naked eye
can be a powerful tool for evaluating whether plants have enough of
all the essential plant nutrients. They allow the farmer to identify the
lacking nutrient and quickly take action to remedy the situation. The
farmer does not have to rely on other people or specialists or wait for
the results of tests.
However, visual nutrient deficiency symptoms can present problems.
• By the time the symptoms appear, the crop has already been
damaged and so growth and yield will be decreased.
• Many of the deficiency symptoms are similar for more than one
nutrient. So, it can be difficult to determine exactly which nutrient is
lacking.
• Plants may show the same deficiency symptoms for other problems
such as disease, drought, salt damage, heat, chemical damage
or water logging. This can lead to the incorrect diagnosis of the
problem.
Bearing in mind the limitations of nutrient deficiency symptoms,
farmers should make use of other diagnostic tools. Such tools
include soil analysis and plant analysis, if possible. Soil analysis is
recommended for identifying nutrient deficiencies for annual crops.
Plant analysis is recommended for testing nutrient deficiencies in
perennial crops. You will learn more about soil analysis in Module 4.
Nutrient deficiency symptoms are still very often the first clue or sign
that there is a nutrient problem in a field. A farmer with knowledge
and experience of the field’s history can interpret deficiency symptoms
quite accurately.
14
Topic 1: Module 1
Words &
Terms
symptom
– a condit
ion that
indicates
the existe
nce of
somethin
g serious
deficient
– not havi
ng enoug
h
Words &
Terms
evaluate
– to
judge the
value of
visual – b
ased on th
e
use of
sight
Types of deficiency symptoms and
terminology
Words &
Terms
Chlorosis
Chlorosis refers to a yellowing of the leaf. Chlorosis is directly
caused by a lack of chlorophyll, the photosynthesis pigment. A lack
of chlorophyll can in turn be caused by a deficiency of any of the
nutrients involved in chlorophyll production and photosynthesis. We
refer to plant tissue that lacks chlorophyll as chlorotic.
It is important to identify the parts of the plant that show chlorosis,
because this can point to which nutrient is deficient. For example
(Figure 1.4):
photosyn
thesis – th
ep
by which
a plant pro rocess
duces
sugars fro
m
and water, carbon dioxide
by action
of
light (radia
nt energy)
on
chlorophyl
l
pigment –
a substan
ce which
gives colo
ur in plan
t or
animal ce
lls
• Overall chlorosis refers to a general yellowing of the leaves as is
caused by nitrogen deficiency.
• Interveinal chlorosis refers to yellowing of the leaf tissue between
the veins, but the veins themselves stay green as caused by iron
deficiency.
• Marginal chlorosis refers to the yellowing of the margins of the leaf
chlorosis as caused by calcium deficiency.
Figure 1.4: (a) overall chlorosis, (b) interveinal chlorosis and (c) marginal chlorosis.
The colour plate on the inside back cover shows photographs of leaves with chlorosis.
Necrosis
Necrosis is the term used to describe the signs of death in any living
tissue. Parts of the plant or the whole plant may die as a result of
nutrient deficiency. We call dead tissue that is still attached to a
living plant necrotic tissue. As with chlorosis, necrosis can take many
forms. Necrotic tissue can be white, grey, light brown, dark brown or
black. Necrosis can be seen in leaves, stems or roots. Necrosis can be
interveinal, veinal, marginal or it may affect only the tips of leaves.
Words &
Terms
tissue – a
group of s
pecialised
cells in an
organism
veinal – o
f veins, i.e
. the
network o
f tubes in
leaves
containing
(and trans
porting)
sap
Unit 3: Symptoms of nutrient deficiencies in crops
15
Figure 1.5: (a) interveinal necrosis, (b) veinal necrosis (c) marginal necrosis and (d)
tip necrosis
Changes in colour
Certain nutrient deficiencies cause the plant or parts of the plant to
change colour from their normal green colour. Colours that indicate
different nutrient deficiencies include white, light green, yellow,
orange, red, purple and very dark green. For example, in maize very
dark green leaves can indicate phosphorus deficiency; leaves with
brown stripes can indicate magnesium deficiency; and purple stems
can indicate iron or phosphorus deficiency (Figure 1.6).
16
Topic 1: Module 1
Figure 1.6: Some colour based signs of nutrient deficiencies in maize (a) leaves with
brown stripes can indicate magnesium deficiency and (b) purple stems can indicate
iron or phosphorus deficiency
Abnormal growth and development
Nutrient deficiencies can lead to abnormal shapes and sizes of stems
and leaves. Stems may be very thin or very thick. Leaves may be
small, rolled, brittle, puckered, torn, wilted or square at the tip
(Figure 1.7).
Figure 1.7: Some abnormal leaf growth (a) rolled leaves and (b) puckered leaves
Stunting
Stunting refers to reduced growth. Stunted plants are shorter than
normal and do not reach their full potential height.
Unit 3: Symptoms of nutrient deficiencies in crops
17
Symptoms of deficiency of the 13 essential nutrients
Macro-nutrient deficiency and toxicity symptoms
TABLE 4: Macro-nutrient deficiency symptoms
Macro-nutrient
Deficiency symptoms
Toxicity symptoms
Nitrogen (N)
• Chlorosis. Older leaves change from normal green to pale
green, then yellow and then yellowish white. The whole
leaf is affected. Young leaves stay green but get much
paler.
• Stunted growth.
• Small leaves.
• Weak stems.
Nitrogen toxicity
• Plants turn dark green
• Plants grow tall weak
stems
• Shoot development is poor
• Vegetative buds form
instead of reproductive
buds
Ammonium toxicity
• Plants stunted
• Lesions occur on stems
and roots
• Leaf margins roll
downward
Phosphorus (P)
• Stunted growth. Slow growth can make phosphorusdeficient plants look like very young, healthy plants.
• Stems, petioles and underside of leaves turn yellow and
then a reddish purple colour.
Note: Phosphorous deficiency symptoms are not very
distinct and can be difficult to identify.
• Reduces uptake of Fe, Mn
and Zn (see deficiency
symptoms for each of
these nutrients)
Potassium (K)
• Chlorosis. Starts with marginal chlorosis. Develops into
interveinal chlorosis. The veins stay green.
• Necrosis. Interveinal chlorosis develops into interveinal
necrosis which appears as dry brown burn marks
developing from the margin inwards to the midrib. The
veins stay green.
• Leaves eventually roll and crinkle.
Note: In some plants such as potatoes and beans, the first
symptom can be small white spots on the leaves.
• Reduces uptake of Mg
and Ca (see Mg and Ca
deficiency descriptions)
Calcium (Ca)
• Necrosis. The growing tips of shoots and young leaves
die, leaving soft dead tissue. Sometimes the petioles
develop but the leaves do not, so there is only a bit of
necrotic tissue at the tip of each petiole.
• Tips of leaves appear hook-shaped.
• Margins of leaves start to roll downwards so that leaves
look like upside-down cups.
• Plants wilt easily.
•
•
•
•
Magnesium (Mg)
• Chlorosis. Begins with mottled chlorotic areas in the
interveinal tissues of older leaves. Veins stay green.
• Interveinal tissue expands and becomes puckered.
• Leaf margins roll upwards or downwards
• Necrosis. Interveinal chlorotic tissue dies.
• Ca and K deficiencies (see
deficiency symptoms of
these nutrients)
Sulphur (S)
• Chlorosis. General chlorosis of all leaves. Old leaves turn
light green. Young leaves turn yellow.
• Young leaves and petioles turn a pale pinkish red or
purple colour.
• Necrosis. Eventually brown necrotic spots may form on
the petioles.
• Leaves can become twisted and brittle.
• Interveinal chlorosis of new
leaves
• Premature death or
dropping of leaves
• Reduced K, Mg, Ca, Mn
(See deficiency symptoms
of these nutrients)
18
Topic 1: Module 1
Leaf distortion
Marginal chlorosis
Marginal necrosis
Mg, B and K deficiencies
(see deficiency symptoms
of these nutrients)
Micro-nutrient deficiency symptoms
TABLE 5: Micro-nutrient deficiency and toxity symptoms
Micro-nutrient
Deficiency symptoms
Toxicity symptoms
Iron (Fe)
• Chlorosis. Begins as interveinal chlorosis in the younger
leaves, followed by general chlorosis of entire leaf, causing
leaves to appear white. If iron fertiliser is added, the veins
become bright green before the rest of the leaf.
• Necrosis. Chlorotic areas develop necrotic spots.
• Tiny brown spots on lower
leaves starting from the tip
• Chlorosis of whole leaves
with leaves turning from
orange-yellow to bronzebrown
Manganese (Mn)
• Chlorosis. Starts with interveinal chlorosis of the young
• Necrotic spots older leaves
leaves. Veins of young and old leaves are visible as dark net
surrounded by chlorotic
patterns when viewed against the light.
circles
• Leaves develop a grey to purple shine.
• New leaves have necrotic
• Necrosis. New leaves have dark necrotic spots. In grain
edges and spots, may be
crops, the necrotic spots are grey and they elongate and join
malformed and stunted
up until the whole leaf dies.
Boron (B)
• Chlorosis followed by
• Chlorosis. There is a light general chlorosis.
necrosis beginning at the
• Necrosis. Growing tips turn brown and die. Necrotic spots
develop on fruits.
leaf tip and margins and
spreading toward the midrib
• Leaves become crinkled and brittle.
• Petioles become dark and brittle. Sometimes a syrupy liquid • Eventually older leaves
appear scorched and fall
is released from the base of the leaf.
prematurely
• Stems may be hollow or roughened.
Molybdenum (Mo)
• Chlorosis. Begins with mottled spots of chlorotic tissue and
develops into larger interveinal chlorotic areas.
• Leaves cup upwards to resemble saucers.
Zinc (Zn)
• Leaves turn dark green
• Chlorosis. Young leaves become yellow. The veins stay
• Inteveinal chlorosis develops
yellow.
• Fe deficiency (see Fe
• Mature leaves develop pits on upper surface of the
deficiency symptoms)
interveinal tissue.
• Leaves and stems are stunted.
• Guttation. Drops of water are forced out along the margins
of the leaves.
• Necrosis. Chlorotic and pitted tissues turn dark and die. The
veins stay green.
Copper (Cu)
• Chlorosis. Young leaves show general light chlorosis.
Mature leaves show green veins with grey to white-grey
interveinal areas.
• Leaf edges look burnt and curled.
• Petioles bend downwards.
• Some leaves develop sunken necrotic spots
• Displaces iron (Fe) from
the plant, causing chlorosis
and other Fe deficiency
symptoms, such as stunted
growth (See Iron deficiency
symptoms)
Cobalt (Co)
Little is known about its deficiency symptoms.
Little is known about its toxicity
symptoms
Chlorine (Cl)
• Chlorosis. Occurs in smooth flat depressions in the
interveinal area
• Wilting of young leaves.
• Bronze colouration on the upper side of the mature leaves.
• Leaves may have abnormal shapes.
Salt injury and leaf burn
• Stunted growth
• Leaves turn yellow-brown
Unit 3: Symptoms of nutrient deficiencies in crops
19
Assessment activity 1
Assignment on identifying deficiency symptoms in crops
1. Draw a table to summarise the deficiency symptoms of plants. The table should be suitable for
you to use as a field reference.
2. Use your table to identify possible nutrient deficiencies in at least two crops in your college
or local area. You may also need to ask local farmers about the history of the development of
symptoms to help identify the deficiency.
3. Write a report outlining the following points:
a) crops studied
b) description of deficiency symptoms (in the order in which they appeared or developed)
c) conclusions about which nutrient/nutrients are deficient.
Assessment activity 2
Short test on deficiency symptoms
1. a) What is chlorosis?
b) Is chlorosis alone a good indicator of which nutrient is deficient? Explain with examples.
2. Describe the symptoms you would expect to find in plants that are deficient in the following
nutrients:
a) nitrogen
d) iron
b) phosphorus
e) copper
c) potassium
3. Which symptoms would you use to distinguish between:
a) sulphur and phosphorous deficiency
b) potassium and magnesium deficiency.
4. What would you do if you could not clearly diagnose a nutrient deficiency using visual
deficiency symptoms?
Assess yourself
Assess your performance in the following activities:
Assignment on identifying nutrient deficiency symptoms
1
2
3
4
1
2
3
4
Short test on nutrient deficiency symptoms
1 = not achieved; 2 = not yet competent; 3 = competent; 4 = outstanding
Unit summary
This unit focuses on the visual symptoms that can indicate nutrient deficiencies in a plant. The
deficiency symptoms for both the macronutrients and micronutrients are described.
20
Topic 1: Module 1