B. H. Nolte
Extension Agricultural Engineer, OSU
N. R. Fausey
Soil Scientist, USDA-ARS
The volume of a typical cultivated silt loam soil is 50 percent soil particles, 30 percent water and 20 percent air. Of course, air and water content are constantly changing. An applied load that reduces the total volume causes compaction. Because the soil particles and water are relatively incompressible, compaction causes reorientation of soil particles and reduces the volume of air. This slows down water and air movement and reduces the water holding capacity of the soil.
Excessive soil compaction may result in poor drainage; increased energy for tillage; reduced crop yields because of reduced water and air movement in the soil; reduced rate of root growth; and delays in tillage, planting and harvesting. Ponding of water on the soil surface in wheel track depressions and on turn rows that receive extra machine traffic usually show the first evidence of excessive compaction.
Drainage systems for crop production are designed to remove excess water from the soil by runoff from the surface or through subsurface drains. Compacting the soil through farming practices will slow infiltration, increase the volume of surface runoff and allow less water to enter the soil profile. More runoff may increase erosion. Because compaction reduces the rate of water movement through the soil, it results in slower soil profile drainage by subsurface (tile) drains. Longer periods of soil saturation may increase denitrification.
Excessive soil compaction causes water problems in two locations, (1) at the soil surface and (2) below the normal tillage depth.
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