Soil erosion is a natural process that occurs in all soils over time, but it’s usually slow enough that the lost soil can be replenished. Soil typically erodes in a three-part process: soil detachment, movement and disposition. A number of variables speed up the rate at which soil erodes, and by controlling these variables you can reduce or minimize erosion in your landscape.
The impact of raindrops on the soil surface can cause the surface layer of soil to break down. Once the soil particles are loosened, they’re carried away with the runoff. Water can cause rills, or narrow fissures to occur in the soil, or larger gullies, which typically are found at the base of sloped areas of landscapes. Hard, driving rains that impact the soil with more force than lighter rains tend to erode soil more rapidly. Soil erosion caused by rainfall is often greatest and most noticeable during short, high-intensity rain storms. Long-lasting, less intense storms also cause erosion, but this isn’t as noticeable because the soil loss isn’t as significant initially.
Soil particles are carried away by the wind in three ways: saltation, surface creep, and suspension. Saltation occurs when soil particles are lifted a short distance by the wind and dropped down on the ground again. Surface creep occurs when large soil particles are dislodged by wind and rolled along the soil surface. Suspension occurs when fine particles of soil are lifted high into the air and carried great distances on the wind. Tilling the soil to create a rough surface and providing adequate moisture during dry or windy periods can minimize the soil’s susceptibility to wind erosion.
The physical characteristics of your soil play a big part in how easily it erodes away. Generally, well-draining soils with high levels of organic matter are resistant to soil erosion because they have good structure and hold together well. For example, coarse sand, sandy loam and loamy soils are less susceptible to erosion than silt, fine sand, and some clay soils. This is because lighter soils such as silt or fine sand are low in organic material and dry rapidly. You can improve the structure and texture of these soils applying organic material, such as compost, leaves or mulch.
The odds that soil will erode increases if the soil is bare of plants or crop residues. These materials act as a barrier over the soil, protecting it from raindrop impact and splash and wind, and they slow down the movement of runoff water. Grass, trees and shrub produce interlocking root systems which help hold soil in place, but in low-lying or sloped areas, a lack of windbreaks such as trees and shrubs can make your soil more vulnerable to wind erosion, even if there is a covering of grass. This is because these areas dry more rapidly than those that have protection from wind, and dry soil is more easily carried by the wind.
The steeper and longer the slope a piece of land is, the higher the risk of erosion will be. This is a simple matter of gravity. The velocity of wind and water is increased on a slope, and it is easier for wind and water to carry the soil downhill than uphill or across a flat stretch of land. Erosion on sloped areas of land can be minimized by providing vegetative cover such as shrubs or deep-rooted plants. You can also modify the slope by adding terraced steps into the slope using natural stone or landscape timbers.