1IntroductionSoil and water conservation is a comprehensive subject on the study of reasonable exploration and utilization of soil and water resources. During the 3000 years' historical practices, Chinese people have gained rich experiences in environmental protection and
improvement. In the 1930s, American scientists, represented by Professor Bennett, set up the subject of "soil conservation" concentrated on soil cultivation. Meanwhile, Russian agronomist who developed the subject of "soil conservation" (Tang etal., 1998) focused on the improvement of soils by appropriate measures of agriculture, forestry and water conservancy. Soil and water conservation is really an interdisciplinary and comprehensive subject for its complicated loss processes and regional distribution
resulted from different human activities and natural factors like climates and landforms. It is closely related in theory with meteorology, hydrology, geology, physiognomy, agrology, botanical ecology, sociology and economics (Zhang etal., 2002). It is related in practice with agronomy (e.g. agricultural mechanization), forestry, stockbreeding, water conservancy, horticulture (e.g. fruit trees, vegetables and flowers), aquiculture, social economics in soil and water conservation, administration in soil and water conservation, system engineering in soil and water conservation (Liu etal., 2001).Soil and water loss has now turned to be a disastrous problem in worsening the global ecological environment. According to the latest statistics, there is a land degradation area of 20
×108 km2 and a loss of 2642×104 km2, accounting for 28.3% of the total global cultivated land area (Wang, 2002).All human economic activities in the world are not only dependent on but also affected by the deteriorating ecological environment, which contrarily hold back the economic development and living standard improvement. Breaking the balance between a strong economic foundation and favorable ecological environment is of negative effect to economic development and even to human survival. With the economic development, population explosion and the moving of human activities from plain to mountainous areas, the social, economic and ecological situations will directly influence the overall developing situation, in which to improve the mountainous ecological environment is the key subject of the whole project of soil and water conservation. Above all, the soil and water conservation shoulders a heavy responsibility with a long way to go (Zhang, 2001).2ThebasiccharacteristicsofsoilandwaterlossinChinaChina has been one of the countries in the world with most serious problem of soil and water loss. This austere confrontation before us with an increasingly expanding area of soil loss and desertification makes our conservation work burden a quite heavy responsibility. The basic characteristics of soil and water loss in China are as follows:2.1WidedistributionAccording to the second national soil erosion remote-sensing survey in 2002, China has at present a loss of 356×104 km2 of land accounting for 37.1% of its total land area. Among which 165×104 km2 are eroded by water, 191×104 km2 by wind (Table 1 and Figure 1), and 26×104 km2 by both (China, 2004).2.2ExpandingareaThe water-eroded area has increased from 116×104 km2 in the 1950s to 165×104 km2 in 2002, of which the total harnessed area is no more than 91×104 km2. The lost area of 4876×104 ha is 38.6% to the total arable land of 1.26×108 ha. The present lost area is 45.4×104 km2,accounting Slight water erosionLight water erosionMedium water erosionLess strong water erosionStrong water erosionExtremely strong water erosionSeverely strong water erosionSlight wind erosionLight wind erosionMedium wind erosionStrong wind erosionExtremely strong wind erosionSeverely strong wind erosionLight freezing-thawingMedium freezing-thawingStrong freezing-thawingExtremely strong freezing-thawingNo obvious erosionFigure 1 Types and intensities of soil erosi
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