Erosion, Soil


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Erosion, Soil

 

the destruction of soil by the action of water and the wind and the subsequent movement and redeposition of the products of destruction.

Erosion by water is manifested on slopes, where rainwater or meltwater flows downhill. It is subdivided into sheet erosion (the relatively uniform removal of soil by the action of running water, excess water that had not been absorbed by the soil), rill erosion (the formation of small rivulets, which can be easily eliminated by ordinary measures), and gully, or channel, erosion (the erosion of soil and rocks by streams of water).

Erosion by wind (seeDEFLATION) occurs on any type of terrain, including plains; it can occur daily (low-velocity winds lift soil particles and carry them elsewhere), or it can be periodic in the form of dust storms, which are strong winds that lift the top layer of soil, sometimes with the plant cover, and carry the soil mass great distances.

According to the degree of destruction, soil erosion is subdivided into geological (or natural) erosion and accelerated erosion, the latter brought about by man’s activities. Geological erosion proceeds slowly, and soil productivity is not decreased. Accelerated erosion is caused by man’s economic activities, namely, improper tillage and irrigation, the destruction of the plant cover by grazing livestock, logging, and construction work.

Intensive soil erosion decreases soil productivity, damages plantings, and causes the silting of rivers and lakes; the gulleys transform agricultural lands into nearly untillable lands and impede tillage. Soil erosion destroys roads and communications lines, power lines, and other forms of transmission.

Soil erosion inflicts great damage to agriculture. This was once particularly so in the USA and Canada, where long-continued overcultivation depleted the soil, and continues to be so in the Mediterranean, Middle East, India, Pakistan, China, southern Africa, and Australia. As a result of soil erosion, in 1975 more than 50 million hectares of all the world’s plowlands were no longer usable. In the USSR, according to state land inventory figures (1975), about 200 million hectares require protection from water erosion (the Central Chernozem Regions and areas along the right bank of the Dnieper, in the Volga Region, on the Don, and in the Northern Caucasus, the mountainous regions of Transcaucasia, and Middle Asia); wind erosion threatens more than 100 million hectares (Northern Kazakhstan, Southern Siberia, southern parts of the Ukraine, the Trans-Volga Region). The latter occurs more often in regions where the soil consists of finegrained particles.

In the USSR, soil erosion control is one of the state’s principal tasks in agricultural development. To this end, various combined agrotechnical, forest-improvement, hydroengineering, and economic-management erosion control measures have been adopted, each group of measures developed specifically for a particular area. Agrotechnical measures include tilling and seeding across slopes, deep (more than 22 cm) tillage alternating every two or three years with ordinary plowing, subsurface plowing, nonmold-board tillage, the loosening in spring of winter cover crops, slotting, and the return of slopes to plant cover. Such measures help regulate the flow of meltwater and rainwater and considerably decrease washout. In areas subjected to wind erosion, agrotechnical measures include subsurface plowing, instead of ordinary plowing, using subsurface cultivators that preserve the stubble (soil-protection tillage technique), which decreases dust dispersion and promotes increased moisture retention of the soil. Of great importance in all regions subjected to soil erosion is protective crop rotation, as well as raising crops between strips of high-stem plants sown earlier to provide snowcatch and windbreak rows. Of the forest-management measures, the most effective are shelterbelts (field-protection, ravine, and gully control shelter-belts). Hydroengineering measures include terracing on steep slopes; water-retaining bands and drainage ditches, chutes, and stepfalls are built along the bottoms of gulleys and ravines. Erosion-control measures are usually planned within the system of land-use management.

REFERENCES

Baraev, A. I., A. A. Zaitseva, and E. F. Gossen. Bor’ba s vetrovoi eroziei pochv. Alma-Ata, 1963.
Pochvozashchitnoe zemledelie. Edited by A. I. Baraev. Moscow, 1975.

E. I. GAIDAMAKA

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But subsequent civilizations, which presumably knew what had happened to those earlier ones, continued to inflict the same abuses--allowing deforestation, erosion, soil depletion, salinization, and contamination to gradually degrade and destroy the land that meant so much to them.
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