The fertile soil layer under natural conditions takes a very long time to form. At the same time, tens of millions of tons of nitrogen, potassium, phosphorus, the main components of plant nutrition, are annually withdrawn from the vast areas occupied by agricultural crops. Soil depletion does not occur only because organic and mineral fertilizers are annually applied to fields in cultivated agriculture. Crop rotation also contributes to the preservation of soil fertility, aimed at creating conditions for the accumulation of nitrogen in the soil (legumes) and hindering the propagation of pests of cultivated plants. Adverse changes in the soil occur when sowing the same crops for a long time, salinization with artificial irrigation, waterlogging with improper reclamation. As a result, soil fertility is gradually declining. It is these processes, along with deforestation, that led to the transformation into deserts and semi-deserts of many areas of ancient agriculture (Egypt, Mesopotamia, Central Asia).
Among the anthropogenic changes in the soil is erosion. Erosion is the destruction and demolition of soil cover by water currents or wind. Especially destructive is water erosion. It develops on slopes with improper cultivation of the land. With melt and rainwater, millions of tons of soil are carried into ravines and ravines from the fields.
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