Soil Degradation

Soil degradation is the alteration of one or more soil properties due to human or natural causes that results in a lowered performance of a soil for a specific function. The term soil degradation is also used to describe alteration of the soil properties associated with a soil's natural or inherent set of physical, chemical, and biological properties. Soil degradation may be a temporary condition or a permanent state, depending on the severity of the degradation and the resilience of the soil to being restored to a functional level for a specific purpose or to its natural inherent state through improved management and/or changes to physical variables (e.g., end of a drought period).

Soil erosion is an example of a soil-degradative process and is often considered to be a temporary condition (see photo). Erosion may be minimized through alteration of land management practices to slow erosion processes and allow the degraded soil properties associated with soil loss to become restored (e.g., the reestablishment of topsoil).

The U.S. Soil Erosion Service, predecessor to the Soil Conservation Service and now the Natural Resources Conservation Service, identified the degradative effects that the intensive agricultural management practices of the early part of the 20th century were having on the rates of soil erosion in the Great Plains region. High levels of topsoil loss during the preceding years, coupled with drought conditions, resulted in decreased agricultural productivity, leading ultimately to the Dust Bowl. To initiate a new era of soil conservation and restoration, the U.S. government implemented agricultural policies aimed at helping farmers use practices known to decrease [Page 2582]erosion and facilitate restoration of the degraded conditions. These new forms of agricultural land management, such as contour plowing and resting land, mitigated the rates of soil erosion and allowed the reestablishment of topsoil. This change led to sustainability in the form of continued agricultural fertility of the soils of the U.S. Great Plains region.

Soil erosion due to water runoff in a grain-producing region of Castilla-La Mancha, Spain, is attributed to a combination of management practices and high-intensity precipitation events typical of Mediterranean winters.

Source: C. Lacasta, Consejo Superior de Investigaciones Científicas, Centro de Ciencias Medioambientales (CSIC-CCMA), Madrid, Spain.

Soil desertification is another example of a soil-degradative condition. It includes several aspects of soil degradation and is generally a condition not considered to be reversible. Some regions in sub-Saharan Africa experience desertification due to population pressures on soil resources combined with climatic factors. The resulting soil degradation in the form of soil compaction and loss of nutrients is so severe, likened to the spreading of desert conditions, that restoration is not generally considered a possibility.

The processes of soil degradation depend on both human and physical variables that affect a soil region. These human and physical variables can change during timescales as short as a human life and include aspects of land management practices and decisions as well as physical environmental factors such as climate change. Improved understanding of human and physical environmental effects on the processes of soil degradation is helpful in developing ongoing management techniques and policies that specifically address current soil degradation issues characteristic of a particular region, thus improving the sustainability of soil function and resources.

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