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The Soil System

The Soil System. Soil is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air and billions of living organisms (microscopic decomposers). Soil formation is a slow process:. Weathering of rock (mechanical). Deposition of sediments by erosion (mechanical).

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The Soil System

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  1. The Soil System

  2. Soil is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air and billions of living organisms (microscopic decomposers).

  3. Soil formation is a slow process: • Weathering of rock (mechanical). • Deposition of sediments by erosion (mechanical). • Decomposition of organic matter in dead organisms (chemical).

  4. Mature soils are arranged in a series of zones called SOIL HORIZONS: “O” HORIZON = freshly fallen and partially decomposed leaves, twigs, animal waste. You can find fungi and other organic materials. “A” HORIZON = porous mixture of partially decomposed organic matter (humus) as well as bacteria, fungi, earthworms, and other decomposer organisms interacting in complex ways. inorganic

  5. “B” (subsoil) and “C” (parent material) HORIZON contain most of the soil’s inorganic matter, mostly broken-down rock consisting of varying mixtures of sand, silt, clay, and gravel..

  6. Soil Content Clay (very fine particles) <0.002mm Silt (fine particles) 0.002-0.05mm Sand (medium-size particles) 0.05-2.0mm Gravel (coarse to very coarse particles) >2.0mm Soil Texture is determined by the relative amounts of the different types and sizes of mineral particles. Loam is soil composed of sand, silt, and clay in relatively even concentration (about 40-40-20% concentration respectively). Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils. Loams are gritty, moist, and retain water easily.

  7. 100%clay 0 clay loam sandy clay loam loamy sand 80 20 silt sandy loam silty loam silty clay loam clay loam sand 60 40 silty clay Increasing percentage clay Increasing percentage silt 40 60 sandy clay 20 80 0 100%sand 80 60 40 20 100%silt Increasing percentage sand Soil Texture Triangle http://www.youtube.com/watch?v=knrmCbctGEA

  8. Soil texture helps determine SOIL POROSITY, a measure of the volume of pores or spaces per volume of soil and the average space between those spaces. INFILTRATION is the downward movement of water through soils. As the water seeps down, it dissolves various soil components in upper layers and carries them down to lower layers in a process called LEACHING.

  9. Water Water High permeability Low permeability SOIL PERMEABILITY is the rate at which water and air move from upper to lower soil layers.

  10. Properties of Soils with Different Textures

  11. Soil erosion is the movement of soil components, especially surface litter and topsoil. • The two main agents of erosion are: • wind • flowing water • Loss of plant cover by farming, logging, construction, overgrazing by livestock, off-road vehicles, deliberate burning of vegetation and other activities leave soil vulnerable to erosion.

  12. serious concern some concern Stable areas • Two major harmful effects of soil erosion: • Loss of soil fertility and its ability to hold water • Runoff of sediment that pollutes water, kills fish and shellfish, and clog irrigation ditches, boat channels, reservoirs, and lakes.

  13. Consequences Causes Overgrazing Deforestation Surface mining Erosion Salinization Soil compaction Worsening drought Famine Economic losses Lower living standards Environmental refugees Desertification is the enlargement of deserts through human activities.

  14. SALINATION • Irrigation water contains small amounts of dissolved salts. • Evaporation and transpiration leave salts behind. • Salt builds up in soil. • WATERLOGGING • Precipitation and irrigation water percolate downward. • Water table rises. • Causes roots to drown. Both result in stunted plant growth, lower crop yields, dead plants and ruined land.

  15. Soil Conservation involves reducing soil erosion and restoring soil fertility. http://www.youtube.com/watch?v=MQQcnId3Z7A

  16. Contour planting and strip cropping: each row acts as a small dam to help hold soil and slow water runoff.

  17. Alley cropping or agroforestry: several crops are planted together in strips or alleys between trees and shrubs that can provide fruit or fuel-wood, shade, help retain and slowly release soil moisture, and fodder for livestock.

  18. Windbreaks or shelterbelts of trees reduce wind erosion, help retain soil, supply wood for fuel, and provide habitats for birds, pest-eating and pollinating insects, and other animals.

  19. Terracing retains water for crops at each level and reduces soil erosion by controlling runoff.

  20. Soil Restoration • Organic fertilizer • Manure • Compost crop rotation • No till farming • Contour farming • Terracing • Nitrogen fixation-legumes

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