Soil Erosion and Conservation on Subtropical Arable in Yunnan Province, South-west China

China has one of the world’s most severe soil erosion problems, extensively reviewed by Wen (1993) and Edmonds (1994) (see also this volume, Chapters 11 and 13). The population is putting severe pressures on the soil resource, which supports 22 per cent of the global population on 7 per cent of the world’s cropland (Brown 1984). The productive soil resource is severely restrained by climate. Much of western China, particularly Xinjiang, Gansu, Ningxia and Inner Mongolia provinces, is too arid, while the Qinghai-Tibetan Plateau of the west is also too cold for extensive crop production (Zhao 1986). Hence, most crops are grown in the humid east. Only about 13.5 per cent (130 million hectares) of total land area is cultivated (Wen 1993). Whilst government policy prohibits cultivation of slopes steeper than 28 per cent (Barrows et al. 1982), this limit is often breached to extend crop production. Land resource pressures exerted by 1200 million people are superimposed on diverse environments, which are often geologically and geomorphologically unstable. Therefore, physical factors, such as slope steepness and stability, tectonic activity, rainfall erosivity and soil erodibility interact with anthropogenic activities, producing the complicated erosion problem. Thus, erosion is produced by a complex interplay of environmental and anthropogenic factors.