Classification based on climate
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Pedalfer: rich in Al, Fe – humid
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Pedocal: rich in calcite (CaCO3)-deserts
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Laterite: rich in Fe oxide – tropics
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Tundra: permafrost – high latitude
Residual soils
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Weathering of bedrock
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Granite: quartz, weathered feldspar, clays
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Shale: Clay rich
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Limestone: CaCO3
Transported soils
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River: Alluvial soil
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Wind: Eolian – e.g. Loess
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Ice: Glacial soils- e.g. Drift
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Eruption: volcanic soil
Soil color
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Dark soils: high organic content
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Red/yellow: high Iron content
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Red: good aeration/drainage
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Yellow: poor aeration/drainage
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White: high CaCO3 (caliche)
Soil Texture (grain size)
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Sand (2- 0.05 mm)
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Silt (0.05-0.002 mm)
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Clay (less than 0.002 mm)
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Loam: mixture of sand, silt, clay
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Classification: % sand, silt, clay
Laterites
• Laterites: tropical climates
• swampy conditions in rainy season; very hard in dry season
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Not very fertile due to leaching
• Source of Aluminum ore- bauxite
Soil Problems- erosion
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Soil non-renewable resource
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Erosion: reduces crop yields
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Puts pesticides and fertilizer into rivers
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Erosion agents: wind and water
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Wind: e.g. 1930 dust bowl – drought
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Water: sheet erosion; rill erosion; gully erosion
Erosion causes
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Overgrazing
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Deforestation
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Bad agriculture practices
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Off road vechicles
Good agricultural practices
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Terracing
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Crop rotation
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Winter groundcover
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No-till farming
Other soil problems
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Expansive soils: clays absorb water and expand – causes movement of foundations
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Permafrost: thawing in summer causes subsidence, soil flows and landslides
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Alaska pipeline- 800 mi; across permafrost – on stilts
Salinization
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Salinization : after intensive irrigation water table is raisedevaporation causes salt to be deposited in soil
Soil contaminants
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Oil-field brines
Heavy metals
Pesticides
Cleaning agents (organic solvents)
Petroleum agents