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Soils: Chemistry and Problems

Soils: Chemistry and Problems. Chapter 8-day three. Soil Properties. Soil Acidity Measured using pH scale 0-7 = acidic 7 = neutral 7-14 = basic pH of most soils range from 4-8 Affects solubility of certain plant nutrients Optimum soil pH is 6-7

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Soils: Chemistry and Problems

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  1. Soils: Chemistry and Problems Chapter 8-day three

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

  3. Acid Rain’s Negative Effects

  4. Chemical Properties of Soil Cation Exchange Capacity- the ability of a soil to adsorb and release cations, positively charged mineral ions. Soil bases- calcium, magnesium, potassium and sodium Soil Acids- aluminum, hydrogen, iron Base saturation- the proportion of soil bases to soil acids

  5. Biological Properties of Soil • Many organisms are found in the soil including fungi, bacteria, protozoans, rodents and earthworms. 10

  6. Soil Organisms • There are millions of microorganisms in 1 tsp of fertile agricultural soil

  7. Soil Organisms • Soil organisms provide ecosystem services • Examples • Decaying and cycling organic material • Breaking down toxic materials • Cleansing water • Soil aeration (especially done by earthworms)

  8. Nutrient Cycling • Nutrients are cycled between plants, organisms and soil

  9. Soil Problems • (1) Soil Erosion • 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 • New Concept: “soil management practices”

  10. Case in Point: American Dust Bowl • Great Plains have low precipitation and 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

  11. Soil Problems • (2) Nutrient Mineral Depletion

  12. Soil Problems • (3) Soil Salinization • Def: gradual accumulation of salt in the soil, usually due to improper irrigation techniques • Often in arid and semi-arid areas • The little precipitation that falls is quickly evaporated • Leaves behind salts • Salt concentrations get to levels toxic to plants

  13. Soil Problems • (4) Desertification • Def: degradation of once-fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert • Typically a human-induced condition • Change in vegetation changes climate, further decreasing precipitation levels

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

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

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

  17. 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

  18. 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 • Required 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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