1
Soils
Chapter 5, continued
2
regolith
nDEF.: a blanket of soil or loose rock fragments on
a planet’
planet’s surface
3
soil
DEF.: the superficial material that forms at the
Earth's surface by organic and inorganic
processes.
4
soil
DEF.: the superficial material that forms at the
Earth's surface by organic and inorganic
processes.
DEF.: pedology _ the study of soils
from "Pedon
" Gk. ground.
"Pedon"
5
Picture of lichen weathering leading to soil formation
6
reasons why geologists like soils
1.
7
8
Provide clues as to the ENVIRONMENT of formation
reasons why geologists like soils
1.
Provide clues as to the ENVIRONMENT of formation
2.
Can be VALUABLE sources of MINERALS
reasons why geologists like soils
1.
Provide clues as to the ENVIRONMENT of formation
1
2.
Can be VALUABLE sources of MINERALS
3. Reflect the NATURE of the rock material from which they
were formed.
9
10
11
An ancient soil in the South Dakota badlands
Typical components in a soil
that yields good plant growth
Factors controlling soil formation
1)Parent
1)Parent material
2)Climate
2)Climate
3)Topography
3)Topography
4)Plants
4)Plants and animals
5)Time
5)Time
12
Factors controlling soil formation
1) Parent material – the bedrock or
sediment from which the soil
develops
13
Factors controlling soil formation
2) Climate
nMost influential
ntemperature and precipitation
14
Factors controlling soil formation
3) Topography – the physical features of a
landscape.
nSteep slopes often have poorly developed
soils
2
nOptimum terrain is flat-to-undulating
15
16
Variations in soil development
due to topography
Factors controlling soil formation
4) Plants and animals
nProduce much of the O2, CO2 and H+ ions
involved in chemical weathering reactions
nH+ replace Ca, K, and Na in feldspars
(hydrolysis)
17
How do plants and animals influence soils?
nAlso furnish organic matter
to the soil
18
Factors controlling soil formation
5) Time
19
An idealized soil profile – Fig. 5.19
20
An idealized soil profile
An idealized soil profile
An idealized soil profile
An idealized soil profile
An idealized soil profile
An idealized soil profile
21
22
23
24
25
26
A soil profile showing
different horizons
27
28
Soil types
nThree very generic soil types
3
nPedalfer
nPedo
Pedocal
nLaterite
29
1) Pedalfer
n Accumulation of iron oxides and Al-rich
Al-rich clays in the B horizon
n Characteristic of forested, humid, temperate regions
30
2) Pedo
Pedocal
nPed = soil
nCal = calcium
nHigh accumulations of calcium carbonate
nAssociated with dry grasslands and brush vegetation; “hot
desert soil.”
soil.”
31
32
3) Laterite
“Extreme”
fer
Extreme” type of pedal
pedalfer
Hot and wet tropical climates
Intense chemical weathering
33
3) Laterite
“Extreme”
Extreme” leaching
Al2Si 2O5(OH) 4 Æ Al 2O3.nH2O + SiO 2
clay
bauxite
34
35
36
Soil erosion
nRecycling of Earth materials
nNatural rates of soil erosion depend on
nSoil characteristics
nClimate
nSlope
nType of vegetation
4
37
Reasons for human-caused soil erosion
n Farming (top soil eroding faster than it forms
on 1/3 of all crop land)
n Logging
n Construction
n Overgrazing
n Overexploitation for fuel wood
38
39
40
What can be done to reduce soil agricultural erosion?
nLeave stubble in the field
nPlant cover crops
nPlant hedges or trees as windbreaks
nLow fences
nPlow rows parallel to the contours of a hill
nterracing
41
End of Chapter 5
5