What is Soil Compaction and When is it a Problem
What is compaction?
Soil compaction occurs when moist or wet soil aggregates are pressed together and the pore space between them is reduced. Compaction changes soil structure, reduces the size and continuity of pores, and increases soil density (bulk density). Wheel traffic or pressure (weight per unit area) exerted on the soil surface by large animals, vehicles, and people can cause soil compaction. In areas of rangeland, compacted soil layers are generally at the soil surface or less than 6 inches below the surface, although they can be as deep as 2 feet under heavily used tracks and roads. Increases in density can be small to large.
When is compaction a problem?
Compaction changes several structural characteristics and functions of the soil. It is a problem when the increased soil density and the decreased pore space limit water infiltration, percolation, and storage; plant growth; or nutrient cycling.
Water movement and storage.—Compaction reduces the capacity of the soil to hold water and the rate of water movement through soil. It limits water infiltration and causes increased runoff and, in some areas, increased erosion. Compacted wheel tracks or trails can concentrate runoff that can create rills or gullies, especially on steep slopes. When the amount of water that enters the soil is reduced, less water is available for plant growth and percolation to deep root zones.
Water entering the soil can perch on a subsurface compacted layer, saturating the soil to or near the surface or ponding on the surface. This water readily evaporates. Compaction can increase the water-holding capacity of sandy soils. An increase in the amount of water stored near the soil surface and a decrease in the amount of water deeper in the soil may favor the shallower rooted annuals over the deeper rooted plant species, such as shrubs.
Plant growth.—Where soil density increases significantly, it limits plant growth by physically restricting root growth. Severe compaction can limit roots to the upper soil layers, effectively cutting off access to the water and nutrients stored deeper in the soil. Anaerobic conditions (lack of oxygen) can develop in or above the compacted layer during wet periods, further limiting root growth. Even in arid climates, anaerobic conditions can occur where water accumulates.
Nutrient cycling.—Compaction alters soil moisture and temperature, which control microbial activity in the soil and the release of nutrients to plants. Anaerobic conditions increase the loss of soil nitrogen through microbial activity. Compaction changes the depth and pattern of root growth. This change affects the contributions of roots to soil organic matter and nutrients. Compaction compresses the soil, reducing the number of large pores. This reduction can restrict the habitat for the larger soil organisms that play a role in nutrient cycling and thus can reduce the number of these organisms.
Please be aware of soil compaction. Take action by preventing compaction in your town. Read up about some causes, effects, and control techniques at this Website