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Chapter 15 Soil Resources. Overview of Chapter 15 o What is soil? o Soil Properties o Major Soil Orders o Soil Problems o Soil Conservation o Soil Reclamation.

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Presentation on theme: "Chapter 15 Soil Resources. Overview of Chapter 15 o What is soil? o Soil Properties o Major Soil Orders o Soil Problems o Soil Conservation o Soil Reclamation."— Presentation transcript:

1 Chapter 15 Soil Resources

2 Overview of Chapter 15 o What is soil? o Soil Properties o Major Soil Orders o Soil Problems o Soil Conservation o Soil Reclamation

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

4 Soil Composition o Mineral Particles (45%) Weathered rock Weathered rock Provides essential nutrients for plants Provides essential nutrients for plants o Organic Material (5%) Litter, animal dung, dead remains of plants and animals, humus (picture) Litter, animal dung, dead remains of plants and animals, humus (picture) o Water (25%) o Air (25%)

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

6 Soil Horizons o O-horizon Rich in organic material Rich in organic material o A-horizon Topsoil Topsoil o B-horizon Lighter colored subsoil Lighter colored subsoil o C-horizon Weathered parent material Weathered parent material

7 Soil Organisms o There are millions of microorganisms in 1 tsp of fertile agricultural soil

8 Soil Organisms o Soil organisms provide ecosystem services Def: Important environmental benefits that ecosystems provide Def: Important environmental benefits that ecosystems provide o Examples Decaying and cycling organic material Decaying and cycling organic material Breaking down toxic materials Breaking down toxic materials Cleansing water Cleansing water Soil aeration (especially done by earthworms) Soil aeration (especially done by earthworms)

9 Nutrient Cycling o Nutrients are cycled between plants, organisms and soil o Example Bacteria and fungi decompose plant and animal wastes Bacteria and fungi decompose plant and animal wastes They are transformed into CO 2, soil nutrients and water They are transformed into CO 2, soil nutrients and water

10 Soil Properties o Soil Texture Relative proportion of sand, silt and clay Relative proportion of sand, silt and clay Sand: 2mm-0.05mm Sand: 2mm-0.05mm Silt: 0.05mm-0.002mm Silt: 0.05mm-0.002mm Clay: >0.002mm Clay: >0.002mm

11 Soil Properties o Soil texture affects soil properties o Coarse textured soil (sandy) Will not hold water well- flows through easily Will not hold water well- flows through easily o Fine textured soil (high in clay) Poor drainage Poor drainage Low oxygen levels in soil Low oxygen levels in soil Due to negatively charged surface, able to hold onto important plant nutrients (K +, Ca 2+, NO 2 - ) Due to negatively charged surface, able to hold onto important plant nutrients (K +, Ca 2+, NO 2 - )

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13 Soil Properties

14 o Soil Acidity Measured using pH scale Measured using pH scale 0-7 = acidic 0-7 = acidic 7 = neutral 7 = neutral 7-14 = basic 7-14 = basic pH of most soils range from 4-8 pH of most soils range from 4-8 Affects solubility of certain plant nutrients Affects solubility of certain plant nutrients Optimum soil pH is 6-7 Optimum soil pH is 6-7 This is the pH where plant nutrients are most available to plants This is the pH where plant nutrients are most available to plants Soil amendments (ex: lime) can be used to achieve this pH Soil amendments (ex: lime) can be used to achieve this pH

15 Soil Problems o Soil Erosion Def: wearing away or removal of soil from the land Def: wearing away or removal of soil from the land Caused primarily by water and wind Caused primarily by water and wind o Why a problem? Causes a loss in soil fertility as organic material and nutrients are eroded Causes a loss in soil fertility as organic material and nutrients are eroded More fertilizers must be used to replace nutrients lost to erosion More fertilizers must be used to replace nutrients lost to erosion o Accelerated by poor soil management practices

16 Case in Point: American Dust Bowl o Great Plains have low precipitation and subject to drought severe drought severe drought No natural vegetation roots to hold soil in place No natural vegetation roots to hold soil in place Replaced by annual crops Replaced by annual crops Winds blew soil as far east as NYC and DC. Winds blew soil as far east as NYC and DC. Farmers went bankrupt Farmers went bankrupt

17 Soil Problems o Nutrient Mineral Depletion

18 Soil Problems o Soil Salinization Def: gradual accumulation of salt in the soil, usually due to improper irrigation techniques Def: gradual accumulation of salt in the soil, usually due to improper irrigation techniques o Often in arid and semi- arid areas The little precipitation that falls is quickly evaporated The little precipitation that falls is quickly evaporated Leaves behind salts Leaves behind salts o Salt concentrations get to levels toxic to plants

19 Soil Problems o Desertification Def: degradation of once- fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert Def: degradation of once- fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert o Typically a human-induced condition o Change in vegetation changes climate, further decreasing precipitation levels

20 Soil Conservation o Conservation Tillage Residues from previous years crops are left in place to prevent soil erosion Residues from previous years crops are left in place to prevent soil erosion Includes no tillage Includes no tillage o Crop Rotation Planting a series of different crops in the same field over a period of years Planting a series of different crops in the same field over a period of years Lessens pest and insect disease Lessens pest and insect disease

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

22 Preserving Soil Fertility o Organic fertilizers Animal manure, crop residue, bone meal and compost Animal manure, crop residue, bone meal and compost Nutrient available to plants only as material decomposes Nutrient available to plants only as material decomposes Slow acting and long lasting Slow acting and long lasting o Inorganic fertilizers Manufactured from chemical compounds Manufactured from chemical compounds Soluble Soluble Fast acting, short lasting Fast acting, short lasting Environmentally sound to limit use Environmentally sound to limit use Mobile- easily leach and pollute groundwater Mobile- easily leach and pollute groundwater

23 Soil Reclamation o Two steps 1. Stabilize land to prevent further erosion 2. Restoring soil to former fertility o Best way to do this is shelterbelts Row of trees planted to reduce wind erosion of soil Row of trees planted to reduce wind erosion of soil

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


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