Soils

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Soils Their PreservationRaven Berg - Chapter
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Properties of Soil

• Soils are formed by two types of weathering of
  bedrock
• mechanical weathering results from physical
  forces that reduce the size of rock particles
  without altering their chemical nature.
• chemical weathering chemically alters the rock so
  that it is more likely to fragment or dissolve.

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• Soil Terminology
• humus partly decomposed organic material in the
  soil brown or black in color.
• soil water and air spaces between soil
  particles may be filled by air and water carrying
  dissolved minerals the only source of these
  materials for plant roots.
• leaching movement of water and dissolved
  material downward through the soil.
• illuviation deposition of a mineral into a
  lower soil layer from a higher layer as a result
  of leaching.

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• Soil Horizons
• horizontal layering of soils
• Soil Profile
• a vertical section from
• surface to parent material

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Major Soil Types
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Destructive Effects of Soil Erosion
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• Loss of up to 70 of topsoil through wind and
  water erosion in some U.S. farmland, and greater
  losses in other countries, leading to
• loss of organic and mineral nutrients needed for
  plant growth, resulting in outright loss of
  farmland and means of food production, or at
  least necessity of heavier application of
  fertilizers.
• siltation of reservoirs and streambeds (clean
  river gravel needed for some fish eggs and
  invertebrates to develop).

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• Soil Conservation
• In order to prevent dust bowl events from
  occurring, various agricultural practices have
  been adopted
• Conservation Tillage
• leaving behind remains of the previous crop to
  keep soil in place
• just under 2/3 of tilled land in the US now uses
  some form of conservation tillage
• No-till relies on pesticides to remove weeds
  instead of plowing

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• Crop Rotation
• changing the crop type from year to year
• helps in reducing pest accumulation
• helps maintain soil nutrients, because different
  plants sequester different amounts of different
  nutrients

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• Contour Farming
• On hilly farmland, creates furrows and/or ridges
  running horizontally across the contour of the
  hill slope.
• runoff water moving down the slope at high
  velocity and causing erosion is captured by these
  furrows or ridges and runs along them to an
  outlet.
• ridges and/or furrows gently slope in the
  direction of the outlet, thereby reducing the
  velocity of the water and its erosion potential.

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• Strip Cropping (Strip Farming)
• Strip cropping involves growing crops in a
  systematic arrangement of contoured or
  across-slope strips to reduce water erosion.
• hybridization between contour farming and crop
  rotation
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• Terracing
• a terrace is an earthen embankment that is
  constructed across a slope to intercept runoff.
• creating level areas along a steep slope to
  retain water and slow erosion.

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• Barriers to Soil Erosion
• Windbreaks (Shelterbelts, Field Borders,
  Hedgerows, Tree Lines)
• windbreaks are permanent vegetation at the edge
  or ends of crop rows.

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• Grassed Waterways
• a grassed waterway is a natural or constructed
  channel, that is planted with grass to protect
  the soil from gully erosion.
• waterways can serve as outlets for terraces or
  diversions, as well as for transporting storm
  water across a field without erosion.

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