Environmental Engineering Reference
In-Depth Information
Fig. 4.1 Landscape position influences soil development (Published with kind permission of US
Department of Agriculture, Natural Resources Conservation Service (
2010b
). Figure is public
domain in the USA. All Rights Reserved)
4.3.1.5 Time
Time is required for horizon formation. The longer a soil surface has been exposed
to soil forming agents like rain and growing plants, the greater the development of
the soil profile. Soils in recent alluvial or windblown materials or soils on steep
slopes where erosion has been active may show very little horizon development.
Soils on older, stable surfaces generally have well defined horizons because the rate
of soil formation has exceeded the rate of geologic erosion or deposition. Relatively
young soils may lack typical hydric soil morphologies due to lack of time to allow
for organic matter accumulation or redoximorphic feature formation.
4.3.2 Soil Forming Processes
The four major processes that change parent material into soil are additions, losses,
translocations, and transformations.
4.3.2.1 Additions
The most obvious addition is organic material. As soon as plant life begins to grow
in fresh parent material, organic material begins to accumulate. Organic matter
gives a black or dark brown color to surface layers. Even young soils may have a
