What Causes Soil Compaction?

Causes

• The primary causes of soil compaction involve equipment, vehicle and pedestrian traffic. Garden equipment such as tractors, lawn mowers, skid-lifts or pickup trunks rolled across the soil eliminate the moisture and air spaces between soil particles. Parking a car on a lawn also causes underlying soil to compact. Excessive, repeated foot traffic from people or animals also collapses a soil's porosity. Often the worn, compacted area of corridor created from heavy wear is colloquially called a cow path. Moist soils that later become extremely dry also may compact as water and air molecules leave the spaces between soil particles.

Factors Affecting Compaction

• Soil structure, parent material and moisture content all contribute to the degree of soil compaction in a landscape. Small-particle soils, such as heavy loam or clay types, compact more readily and easily compared to gritty, sandy soils. If a coarse-grained soil contains organic matter, the compaction may more readily occur. Moist soil compact most severely when compared to very dry or waterlogged soils, according to Kansas State University. However, if machinery or vehicles are heavy enough, compaction occurs regardless of soil qualities.

Alleviating Soil Compaction

• In lawns, compaction caused by foot traffic or parked cars may be somewhat remedied through core aeration. The holes into the top 2 to 3 inches of soil help water and air to penetrate downward again. Deep tillage, to a depth of 8 to 12 inches, is the best way to remedy soil compaction. If the garden already exist with mature plantings, especially with wide-spreading tree roots, tilling may not be feasible. Stop further compaction in the area by not moving heavy machinery, vehicles or unnecessary foot traffic across the area. Especially avoid any heavy treading on soils that are moist to wet, as that will compound compaction.

Avoiding Compaction

• In garden beds or above the expansive root zone of trees, placing a coarse mulch about 3 to 4 inches deep can diminish minor compaction from foot traffic and small maintenance equipment. Vehicles should remain on pavement drives or worn tire tracks across a property -- park on pavement or designated gravel areas and not on bare soil or turf. If heavy machinery must drive across a landscape, placing thick plywood under tires as the vehicle moves helps distribute weight and not create intense ruts or compaction. Dry soils compact less than moist or wet soils, so schedule before rainfall is expected or turn off irrigation well before any trekking across the soil must occur.