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Plants and Soil Soil Degradation Addressing Soil Degradation
Soil characteristics Soil classes (or orders): From richest (and
darkest) to least fertile – mollisols, oxisols, alfisols, and aridisols
Soil profiles – layers of soil produce horizons Soil texture – depends on proportions of
clay, sand, and silt and classified according to the soil texture triangle
Texture affects workability, infiltration, and aeration
Alfisol: Moderately weathered
Andisol: Volcanic ash
Aridisol: Very dry
Entisol: Newly formed
Gelisol: Frozen
Histosol: Organic, wet
Inceptisol: Slightly developed (young)
Mollisol: Deep, fertile
Oxisol: Very weathered
Spodosol: Sandy, acidic
Ultisol: Weathered
Vertisol: Shrinks and swells
Soil TypesThere are 12 types of soils, which soil scientists call soil orders. The soil orders system is similar to the one biologists use to classify animals or plants into groups:
Nutrient-holding capacity: affected by weathering, leaching, and decomposition
Water-holding capacity: affected by transpiration rates, infiltration, irrigation
Aeration Amount of compaction pH Salinity
To support a good crop – soil must have a good supply of nutrients, allow infiltration, have good aeration, neutral pH, and low salt content
Sandy soil is poor Silt and loam are the best Detritus and organisms enrich soil
Bacterial composting Earthworms contribute castings symbiosis
Mineralization: loss of humus leads to the build-up of particles and minerals
Erosion Splash erosion – initial, due to rainfall Sheet erosion – resulting from decreased
infiltration Gully erosion – caused by pressure of
greater amounts of running water
Desertification: spread of degraded areas of soil and vegetation Desert pavement – formed when wind erosion
carries the smaller particles and leaves larger pebbles covering soil below (aggravated by human impact)
Drylands Cover 1/3 of earth’s land area UN ‘s Convention to Combat desertification
Causes that expose soil to erosion: Overcultivation Overgrazing Deforestation Irrigation leading to salinization
Corrections Rotating crops No-till agriculture Contour-strip cropping Shelterbelts
Goals of soil conservation on the individual and public policy levels Maintain productive topsoils Keep food safe and wholesome Reduce chemical fertilizers and pesticides Keep farms economically viable
USDA Low Input Sustainable Agriculture provides funding for alternative farming methods
Conservation Reserve Program pays farmers not to farm land
Food Security Act of 1985 provide incentives for soil conservation
Federal Agricultural Improvement and Reform Act: “Freedom to Farm”
Fostering sustainable agriculture U.S.Superfund/CERCLA have cleaned up areas
polluted by toxins. Soil Conservation Act and SC Service combat
erosion.