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Soil erosion is a major environmental and agricultural problem worldwide. Although erosion has occurred throughout the history of agriculture, it has intensified in recent years (1). Each year, 75 billion metric tons of soil are removed from the land by wind and water erosion, with most coming from agricultural land (2). The loss of soil degrades arable land and eventually renders it unproductive. Worldwide, about 12 X 10 sup 6 ha of arable land are destroyed and abandoned annually because of nonsustainable farming practices (1), and only about 1.5 X 10 sup 9 ha of land are being cultivated (3, 4). Per capita shortages of arable land exist in Africa, Asia, and Europe because of lost eroded land and the expansion of the world population to nearly 6 billion (1, 5).
To adequately feed people a diverse diet, about 0.5 ha of arable land per capita is needed (6), yet only 0.27 ha per capita is available. In 40 years, only 0.14 ha per capita will be available both because of loss of land and rapid population growth (5). In many regions, limited land is a major cause of food shortages and undernutrition (4, 7). Over 1 billion humans (about 20% of the population) now are malnourished because of food shortages and inadequate distribution (8, 9). With the world population increasing at a quarter of a million per day and continued land degradation by erosion, food shortages and malnutrition have the potential to intensify (10, 11).
The use of large amounts of fertilizers, pesticides, and irrigation help offset deleterious effects of erosion but have the potential to create pollution and health problems, destroy natural habitats, and contribute to high energy consumption and unsustainable agricultural systems. Erosion also is a major cause of deforestation: As agricultural land is degraded and abandoned, more forests are cut and converted for needed agricultural production (12).
In this article, we (i) examine the ways in which erosion reduces soil fertility and crop productivity, (ii) assess the environmental and economic costs of soil erosion, and (iii) compare various agricultural techniques and practices that reduce erosion and help conserve water and soil resources.
Erosion on Croplands and Pastures
Worldwide erosion rates. Of the world's agricultural land, about one-third is devoted to crops...