2f. Soil Erosion and Conservation

Geologic Erosion

  • process that transforms soil into sediment

  • takes place naturally without the influence of human activities

  • geologic erosion is greatest in semiarid regions

    • rain is not enough to be damaging

    • not enough to support plant life that would have protected the soil

Accelerated Erosion

  • occurs when people disturb the soil or the natural vegetation by:

    • overgrazing lovestock

    • cutting forests

    • plowing hillsides

    • tearing up land for construction projects

  • can be 10 to 1000 times as destructive as geologic erosion

  • erosion rates

    • US: avg on cropland is 12 Mg/ha (5.4 tons/ac)

      • 7 Mg/ha (3.1 tons/ac) by water

      • 5 Mg/ha (2.2 tons/ac) by wind

    • cultivated soils in africa and asia can be 10 times that

Effect of raindrops

  • bigger raindrops are more erosive

    • faster, more energy at point of impact

  • splash

    • moves soil in all directions

    • if on a slope, more soil splashes downhill

      • net movement of soil downslope

    • raindrops are more important than running water

      • if soil is covered and protected, its less likely to move

sheet erosion

  • splashed soil is moved uniformly

  • columns of soil remain where pebbles protected soil from raindrop impacts

rill erosion

  • running water gathers into small channels due to irregularities on the soil surface

  • those channels incise into the soil surface

  • can be smoothed by tillage, but damage is already done

  • location of rills is random

interrill erosion

  • sheet erosion that takes place between rills

gully erosion

  • rill erosion that cannot be smoothed by tillage equipment

ephemeral gullies

  • similar concept to “ephemeral stream”

  • follows the slope

  • similar to rill erosion

    • can be smoothed by tillage

  • different from rill erosion

    • not random, always occurs in same location

  • if not managed, can cause permanent damage

conservation practices

  • contour cropping

    • pool water

  • contour strip-cropping

    • both slow flow of runoff

  • terraces

    • shorten length of slope

  • grassed waterways

    • slow runoff

  • conservation tillage - no till