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FAO SOILS PORTAL

Management and Natural Processes affecting the biological and chemical aspects of soils

In addition to physical soil health, chemical and biological soil health can be damaged and degraded. Three major aspects of chemical soil degradation are soil nutrient mining, salinization and pollution.

Soil Nutrient Mining

Combined effect of Soil nutrient mining and pollution and corresponding rating

Nutrient depletion of soils is a widespread soil degradation phenomenon that occurs as a consequence of soil erosion (it is the topsoil in which generally most soil nutrients are present that erodes fastest) but also because of poor management practices, such as slash and burn and other subsistence agricultural practices that do not replenish the nutrients taken out the soil by the crops. Note that nutrient mining is only considered in agricultural areas. No nutrient depletion is expected under other land uses (forestry, pastures). Specific studies concerning nutrient balances are of particular use at local and regional scale. See also, the FAO fertilizer and plant nutrition bulletin #14, Assessment of soil nutrient balance - Approaches and Methodologies.

Soil Pollution

Another aspect of importance to the soil chemical health is the absence of toxic substances in the soil. These are associated with very high input and management levels for instance cadmium toxicity related to high phosphorus applications, while the use of excessive N- fertilizer often leads to pollution of the groundwater.

Salinization

Salinization risk estimate of irrigated areas

Salinization occurs generally because of inadequately maintained irrigation systems.  In order to characterize the salinization risk the overall national salinization data from AQUASTAT and SOLAW are used. Only drylands areas are considered as salinized.