lect03-23-10

lect03-23-10 - Soil Texture & Chemical Properties...

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Unformatted text preview: Soil Texture & Chemical Properties soil texture (porosity, permeability) helps determine suitability of soil for agriculture (water & nutrient holding capacity, water infiltration capacity, workability) loam is soil with roughly equal parts of clay, sand, silt and humus - loam is ideal for growing most crops uptake of soil nutrients by plants is reduced in acidic soils (pH value below 5.5) Soil Erosion & Its Consequences soil erosion is the movement of soil components, especially litter & topsoil, from one place to another the agents of erosion are wind and/or flowing water losing topsoil makes soil less fertile & less able to hold water sediment is also a major water pollutant Soil Erosion - A Worldwide Problem while soil is a potentially renewable resource, it takes a long time to form topsoil topsoil is eroding faster than it forms in about onethird of the world's cropland Soil Erosion - A Worldwide Problem about 7% of the world's topsoil is lost from productive land in each decade Types of Soil Erosion Caused by Water sheet erosion - uniform layers (sheets) of soil are peeled off across a field rill erosion - fast flowing water cuts small channels in soil gully erosion - extreme form of rill erosion in which small channels merge and become deeper to form gullies and ditches Desertification desertification of arid & semi-arid lands results when land productivity drops by at least 10% moderate: 10 - 25% severe: 25 - 50% very severe: more than 50% Soil Erosion in the United States During the 1930s, a combination of drought & poor soil conservation led to severe wind erosion of topsoil in what is known as the Dust Bowl of the Great Plains Soil Erosion - Solutions land reclamation reforestation, gully reclamation prevention take vulnerable lands out of production, practice soil conservation Soil Conservation Measures conservationtillage farming minimizes soil disturbance terracing protects steep slopes contour farming follows natural land contours on gentle slopes strip cropping maintains strips of different vegetation between crops alley cropping grows crops between rows of trees crop rotation restores nutrients and also reduces soil erosion windbreaks protect against wind erosion Terracing Contour Farming & Strip Cropping Alley Cropping Windbreaks Other Problems of Irrigation: Soil Salinization & Waterlogging soil salinization irrigation water carries salts which may build up to levels that decrease yields or prevent cultivation Other Problems of Irrigation: Soil Salinization & Waterlogging soil salinization -irrigation water carries salts which may build up to levels that decrease yields or prevent cultivation waterlogging excessive irrigation water raises the water table & lowers crop productivity Food Resources productivity and profitability of agriculture protection from pests sustainable agriculture distribution of food - hunger, poverty, nutritional adequacy government policies related to production and distribution Types of Agricultural Systems industrialized & plantation agriculture: uses large amounts of fossil fuel, water, mechanical equipment, fertilizers & pesticides to produce huge quantities of single crops or livestock Types of Agricultural Systems traditional susbsistence agriculture: uses primarily human labor & draft animals to produce enough crops or livestock for a family's survival examples - shifting cultivation, nomadic herding Types of Agricultural Systems intensive traditional agriculture: uses increased inputs of labor, fertilizer, & water to achieve higher yields for sale Map of Agricultural Systems ...
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