Soil and Its Uses

1
Soil and Its Uses

• Chapter 14

2
Geologic Processes

• Crust - Extremely thin, less-dense solid.
• Mantle - Makes up majority of earth, and
  surrounds a small core of iron.
• Outermost portion is solid.
• Crust and solid outer mantle collectively known
  as the lithosphere.
• Asthenosphere is a thin layer below the outer
  mantle capable of plastic flow.

3
Structure of the Earth
4
Geologic Processes

• Plate Tectonics - Large plates of crust and outer
  mantle slowly moving over surface of the liquid
  outer mantle.
• Heat from earth core causes movement.
• Plates are pulling apart in some areas, and
  colliding in others.
• Building processes counteracted by processes
  tending to tear down land.

5
Tectonic Plates
6
Geological Processes

• Weathering - Factors bringing about fragmentation
  or chemical change of parent material.
• Mechanical - Results from physical forces
  reducing size of rock particles without changing
  the chemical nature of the rock.
• Freezing and Thawing Cycles
• Erosion from Wind and Moving Water

7
Physical Fragmentation
8
Weathering

• Chemical - Involves the chemical alteration of
  rock in such a manner that it is more likely to
  fragment or be dissolved.
• Rock fragments exposed to atmosphere may oxidize,
  or otherwise chemically change.

9
Soil and Land

• Land - Portion of world not covered by water.
• Soil - Mixture of minerals, organic material,
  living organisms, air, and water that together
  support growth of plant life.
• Good Agricultural Soil
• 45 Mineral
• 25 Air
• 25 Water
• 5 Organic Matter

10
Soil Formation

• Soil formation begins with fragmentation of
  parent material.
• Ancient layers of rock, or more recent deposits
  from lava flows or glacial activity.
• First organisms to gain a foothold in weathered
  parent material also contribute to soil
  formation.
• Lichens form pioneer community.
• Decomposition of lichens further alters
  underlying rock.

11
Soil Formation

• Humus - Decaying organic material.
• Mixes with top layers of rock particles, and
  supplies needed nutrients to plants.
• Creates crumbly soil which allows adequate water
  absorption and drainage.
• Burrowing animals bring nutrients up from deeper
  soil layers, improving soil fertility.

12
Other Factors Influencing Soil Formation

• Plant Roots
• Bacteria and Fungi (Decomposers)
• Position on Slope
• Climate
• Time
• Rainfall
• Soil pH

13
Soil Properties

• Texture - Determined by the size of mineral
  particles within the soil.
• Too many large particles leads to extreme
  leaching.
• Too many small particles leads to poor drainage.
• Gravel gt2.0 mm
• Sand 0.05 - 2.0 mm
• Silt 0.002-0.05 mm
• Clay lt 0.002 mm

14
Soil Texture
15
Soil Properties

• Structure - Refers to the way various soil
  particles clump together.
• In good soils 2/3 of intra-soil spaces contain
  air after excess water has drained.
• Friable - Crumbles easily.
• Protozoa, nematodes, earthworms, insects, algae,
  bacteria, and fungi are typical inhabitants of
  soil.

16
Soil Profile

• Soil Profile - A series of horizontal layers of
  different chemical composition, physical
  properties, particle size, and amount of organic
  matter.
• Each recognizable layer of the profile is known
  as a horizon.

17
Soil Horizons

• O Horizon - Litter - Un-decomposed or partially
  decomposed organic material.
• A Horizon - (Topsoil) Uppermost layer - contains
  most of the soil nutrients and organic matter.
• E Horizon - Formed from leaching darker
  materials.
• Not formed in all soils.
• Usually very nutrient poor.

18
Soil Horizons

• B Horizon - (Subsoil) Underneath topsoil.
  Contains less organic matter and fewer organisms,
  but accumulates nutrients leached from topsoil.
  Poorly developed in dry areas.
• C Horizon - Weathered parent material, very
  little organic material.
• R Horizon - Bedrock

19
(No Transcript)
20
Soil Profiles

• Over 15,000 separate soil types have been
  classified in North America. However, most
  cultivated land can be classified as either
  grassland or forest soil.
• Grassland Soils - Usually have a deep A Horizon -
  low rainfall limits topsoil leaching.
• A Horizon supports most root growth.

21
Soil Profiles

• Forest Soils - Topsoil layer is relatively thin,
  but topsoil leachate forms a subsoil that
  supports substantial root growth. (High rainfall
  areas)
• Tropical Rainforests
• Two features of great influence
• High Temperatures
• Rapid decomposition, little litter.
• High Rainfall
• Excessive leaching of nutrients.

22
Major Soil Types
23
Soil Erosion

• Erosion - Wearing away and transportation of soil
  by wind, water, or ice.
• Worldwide removes 25.4 billion tons/yr.
• Made worse by deforestation and desertification.
• Poor agricultural practices increase erosion and
  lead to the transport of associated fertilizers
  and pesticides.

24
Soil Erosion

• Most current agricultural areas lose topsoil
  faster than it can be replenished.
• Wind erosion may not be as evident as water
  erosion, but is still common.
• Most common in dry, treeless areas.
• Great Plains of North America have had four
  serious bouts of wind erosion since European
  Settlement in the 1800s.

25
Worldwide Soil Erosion
26
Soil Conservation Practices

• When topsoil is lost, fertility is reduced or
  destroyed, thus fertilizers must be used to
  restore fertility.
• Raises food costs, and increases sediment load in
  waterways.
• Over 20 of U.S. land is suitable for
  agriculture, but only 2 does not require some
  form of soil conservation practice.

27
Soil Conservation Practices

• Agricultural Potential
• Worldwide
• 11 land surface is suitable for crops.
• 24 in permanent pasture.
• United States
• 20 land surface suitable for crops.
• 25 in permanent pasture.
• African Continent
• 6 land surface suitable for crops.
• 29 can be used for pasture.

28
Soil Conservation Practices

• Contour Farming - Tilling at right angles to the
  slope of the land. Each ridge acts as a small
  dam.
• Useful on gentle slopes.
• Strip Farming - Alternating strips of closely
  sown crops to slow water flow, and increase water
  absorption.
• Terracing - Level areas constructed at right
  angles to the slope to retain water.
• Good for very steep land.

29
Soil Conservation Practices

• Waterways - Depressions in sloping land where
  water collects and flows off the land.
• Channels movement of water.
• Windbreaks - Planting of trees or other plants
  that protect bare soil from full force of the
  wind.
• Reduces wind velocity decreasing the amount of
  soil that can be carried.

30
Conventional vs. Conservation Tillage

• Plowing has multiple desirable effects
• Weeds and weed seeds are buried or destroyed.
• Crop residue is turned under.
• Decays faster and builds soil structure.
• Leached nutrients brought to surface.
• Cooler, darker soil brought to top and warmed.

31
Problem

• Each trip over the field is an added expense to
  the farmer, and at the same time increases the
  amount of time the soil is open to erosion via
  wind or water.
• Reduced Tillage - Uses less cultivation to
  control weeds and prepare soil, but generally
  leaves 15-30 of soil surface covered with crop
  residue after planting.

32
Problem

• Conservation Tillage - Further reduce amount of
  disturbance and leaves 30 or more of soil
  surface covered with crop residue.
• Mulch Tillage - Tilling entire surface just prior
  to planting.
• Strip Tillage - Tilling narrow strips.
• Ridge Tillage - Leave ridge.
• No Till - Place seeds in slits.

33
Positive Effects of Reduced Tillage

• Wildlife gain food and cover.
• Less runoff - reduced siltation of waterways.
• Row-crops can be planted in sloped areas.
• Fewer trips means lower fuel consumption.
• Double - cropping
• Fewer trips means less soil compaction.

34
Drawbacks of Conservation Tillage

• Plant residue may delay soil warming.
• Crop residue reduces evaporation and upward
  movement of water through the soil.
• Accumulation of plant residue can harbor plant
  pests and diseases requiring more insecticides
  and fungicides.

35
Protecting Soil on Non-Farm Land

• By using appropriate soil conservation practices,
  much of the land not usable for crops can be used
  for grazing, wood production, wildlife
  production, or scenic and recreational purposes.

36
(No Transcript)
37
Fig. 14.1
38
Fig. 14.2
39
Fig. 14.4
40
Fig. 14.5
41
Fig. 14.7
42
Fig. 14.8
43
Fig. 14.10
44
Fig. 14.11
45
Fig. 14.12
46
Fig. 14.15
47
Fig. 14.16
48
Fig. 14.17
49
Fig. 14.18
50
Fig. 14.19
51
Fig. 14.20
52
Fig. 14.21
53
Fig. 14.22
54
Fig. 14.23
55
Fig. p.324
56
Fig. p.326
57
(No Transcript)
58
Table 14.2
59
(No Transcript)