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Soil and Its Uses

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Soil and Its Uses Chapter 14 * – PowerPoint PPT presentation

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Title: 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
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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
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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
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58
Table 14.2
59
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