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Chapter 15 Soil Resources

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Title: Chapter 15 Soil Resources


1
Chapter 15 Soil Resources
2
Overview of Chapter 15
  • What is Soil?
  • Soil Horizons
  • Nutrient Cycling
  • Soil Properties and Major Soil Types
  • Soil Problems
  • Soil Conservation and Regeneration

3
Soil
  • Uppermost layer of Earths crust that supports
    plants, animals and microbes
  • Soil Forming Factors
  • Parent Material
  • Time
  • Climate
  • Organisms
  • Topography

4
Soil Composition
  • Mineral Particles (45)
  • Weathered rock
  • Organic Material called humus (5)
  • Leaf litter, animal dung, dead remains of plants
    and animals
  • Water (25)
  • Air (25)

5
Soil Composition
  • Pore space
  • 50 of soil
  • Soil air - good for aeration
  • Soil water - provides water to roots

6
Soil Horizons soil separates naturally over
time into distinct layers
7
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8
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9
Soil Organisms
  • There are millions of microorganisms in 1 tsp of
    fertile agricultural soil

10
Soil Organisms
  • Soil organisms provide ecosystem services
  • Def Important environmental benefits that
    ecosystems provide
  • Examples
  • Decaying and cycling organic material
  • Breaking down toxic materials
  • Cleansing water
  • Soil aeration

11
Nutrient Cycling
  • Nutrients are cycled between plants, organisms
    and soil
  • Three major nutrients needed for plant growth are
    Nitrogen, Phosphorous, and Potassium

12
Soil Properties
  • Soil Texture
  • Relative proportion of sand, silt and clay
  • Sand 2mm0.05 mm
  • Silt 0.05mm0.002 mm
  • Clay gt0.002 mm

13
What type of soil texture will the following soil
compositions produce?
2) 80 silt, 10 sand, 10 clay
_________________
4) 40 silt, 40 sand, 20 clay
_________________________
LOAM IS THE BEST AGRICULTURAL SOIL! WHY???
1) 20 silt, 50 sand, 30 clay
______________________
3) 5 silt, 85 sand, 10 clay
__________________________
14
Soil Properties
  • Soil texture affects soil properties
  • Coarse textured soil (sandy)
  • Excellent drainage
  • Fine textured soil (high in clay)
  • Poor drainage
  • Low oxygen levels in soil
  • Due to negatively charged surface, able to hold
    onto important plant nutrients (K, Ca2, NO2-)

15
This is a close up of a clay particle with a film
of water around it. Positive ions are attracted
to the negatively charged clay surface.
16
Soil Properties

17
Soil Properties
  • Soil Acidity
  • Measured using pH scale
  • pH of most soils range from 48
  • Affects solubility of certain plant nutrients
  • Optimum soil pH is 67, because nutrients are
    most available to plants at this Ph
  • Since rain is naturally acidic, and since plant
    decomposition produces acids (humic acid), and
    since air pollution with sulfur dioxide and
    nitrous oxides leads to acid deposition, LIME can
    be added to soils to increase the pH.
  • LIME IS ESSENTIALLY CALCIUM CARBONATE

18
Major Soil Groups
  • Variations in soil forming factors cause
    variation in soils around globe
  • Soil Taxonomy
  • Separates soils into 12 orders
  • Subdivided into more than 19,000 soil series that
    vary by locality
  • Five common soil orders
  • Spodosols, alfisols, mollisols, aridosols, oxisols

19
Major Soil Groups
  • Spodosols
  • Form under coniferous forests
  • O-horizon composed of decaying needles
  • E-horizon is ash -gray under A-horizon
  • Not good farmland - too acidic

20
Major Soil Groups
  • Alfisols
  • Brown to gray-brown A-horizon
  • Precipitation high enough to leach most organics
    and nutrients out of O-, A- and B-horizons
  • Soil fertility maintained by leaf litter

21
Major Soil Groups
  • Mollisols
  • Found in temperate, semi-arid grassland
  • Very fertile soil
  • Thick, dark brown/ black A-horizon
  • Soluble nutrients stay in A-horizon due to low
    leaching

22
Major Soil Groups
  • Aridosols
  • Found in arid regions of all continents
  • Low precipitation preclude leaching and growth of
    lush vegetation
  • Development of salic horizon possible

23
Major Soil Groups
  • Oxisols
  • Found in tropical and subtropical areas with high
    precipitation
  • Very little organic material accumulation due to
    fast decay rate
  • B-horizon is highly leached and nutrient poor

24
Soil Problems
  • Soil Erosion
  • Caused primarily by water and wind
  • Why a problem?
  • Causes a loss in soil fertility as organic
    material and nutrients are eroded
  • More fertilizers must be used to replace
    nutrients lost to erosion
  • Accelerated by poor soil management practices

25
Soil Erosion by Water and Wind

26
Case in Point American Dust Bowl
  • Great Plains has low precipitation and is subject
    to drought
  • 1930-1937 severe drought
  • No natural vegetation roots to hold soil in place
  • Replaced by annual crops
  • Winds blew soil as far east as NYC and DC.
  • Farmers went bankrupt

27
Soil Problems
  • Nutrient Mineral Depletion

28
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29
Soil Problems
  • Soil Salinization
  • Gradual accumulation of salt in the soil, usually
    due to improper irrigation techniques
  • Often in arid and semi-arid areas
  • Salt concentrations get to levels toxic to plants

30
Soil Problems
  • Desertification
  • Def degradation of once-fertile rangeland,
    agricultural land, or tropical dry forest into
    nonproductive desert

31
Soil Conservation
  • Conservation Tillage
  • Residues from previous years crops are left in
    place to prevent soil erosion
  • Crop Rotation
  • Planting a series of different crops in the same
    field over a period of years

32
Soil Conservation
  • Contour Plowing
  • Plowing around hill instead of up-down
  • Strip Cropping
  • Alternating strips of different crops along
    natural contours
  • Terracing
  • Creating terraces on steep slopes to prevent
    erosion

Strip Cropping
Terracing
33
Preserving Soil Fertility
  • Organic fertilizers
  • Animal manure, crop residue, bone meal and
    compost
  • Nutrient available to plants only as material
    decomposes
  • Inorganic fertilizers
  • Manufactured from chemical compounds
  • Soluble
  • Fast acting, short lasting
  • Mobile- easily leach and pollute groundwater

34
Soil Reclamation
  • Two steps
  • Stabilize land to prevent further erosion
  • Restoring soil to former fertility
  • Best way to do this is shelterbelts
  • Row of trees planted to reduce wind erosion of
    soil

35
Soil Conservation Policies in US
  • Soil Conservation Act 1935
  • Authorized formation of Soil Conservation
    Service, now called Natural Resource Conservation
    Service (NRCS)
  • Assess soil damage and develop policies to
    improve soil
  • Food Security Act (Farm Bill) 1985
  • Farmers with highly erodible soil had to change
    their farming practices
  • Instituted Conservation Reserve Program
  • Pays farmers to stop farming highly erodible land
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