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.