Soil is degraded due to human or environmental influence. Degradation of soil is a major concern to crop farmers and even the home gardener, as mismanaged soil loses its ability to grow vegetation, and often exhibits desertification, where topsoil becomes dry and blows away. There are around six different types of soil degradation.
Erosion, according to the Food and Agriculture Organization of the United Nations, is the detachment of material from the upper crust of the earth by water, wind or ice. Sheet erosion is due to trampling of the soil by human activity or by heavy rainfall. Wind erosion is caused when vegetation is stripped from an area of land and wind slowly dries, then blows away topsoil. Gully erosion happens after sheet erosion, forming tracks where the heaviest erosion has occurred, creating gullies.
High salt levels occurring in soil, according to the ACS Horticulture College gardening website, reduces plants ability to grow in a soil. Discharge of saline groundwater into surface soil is due to large scale vegetation clearing, which reduces the amount of water absorbed by plants, causing ground water to rise. As saline groundwater rises to the level of plant roots, vegetation dies.
Acidic soil is when the soil pH is below 7.0, caused by a rise of hydrogen ions in the soil. Acidic soil prevents plants from gaining access to certain nutrients, according to ACS Gardens. The use of fertilizers that leave acidic residues and the growing of vegetables that have a large amount of base ions, such as legumes, contributes greatly to soil acidity.
Compaction is the pressing down of soil, which reduces the pore space for water seepage and plant roots. Compaction is caused by the running of large machinery over a soil area, livestock traffic and foot traffic says Dominic Ballayan, from the Food and Agriculture Organization of the United Nations.
Continued use of pesticides, insecticides and chemical fertilizer contribute to chemical residues building up in a soil. The repeated use of the same chemicals in a localized area is the main cause. Contaminated areas of the soil, according to ACS Gardens, may require the soil laying unused for several years.
Nutrient loss in soil is caused by overplanting an area with quick harvests, according to the University of Michigan. Planting the same crops in the same area will also result in nutrient loss, as it causes an imbalance in the soil. Allowing soil to rest, or rotating crops, along with good fertilization, are the best management techniques.