Introduction
Natural resources and environment are the bases for human social and agricultural development. China has a vast territory, a large population, and abundant natural resources. The total land area of China is 960 million hectares, which accounts for 1/15 of the total world land area. However, the average land area per person in China is only one-third of that in the world overall. The unusable land area, including deserts, glaciers, tundra, exposed rock, and other area, accounts for 28% of the total land area in China. The desertified (wind-eroded) and potentially desertified land areas account for 3.5%, and the water-eroded land areas account for 15.6%. The total cultivated land area is only 130 million hectares, or 13.5% of the total land area of China (Liu Yingqiu, 1988). About 6.7 million hectares, or 5% of total cultivated land, have become deserts. About 8 million hectares of land, or 6%, are too saline for cultivation. About 42 million hectares of China's cultivated land, or one-third of the total cultivated land, are undergoing serious water and wind erosion. Only a quarter of the cultivated land is well managed and highly productive (Peng Fude, 1987). Obviously, protecting land resources and improving land productivity are essential to feeding more than a thousand million people and for economic development in China. Clearly, controlling soil erosion and improving eroded lands are important tasks for effective management of land resources in China.