Soil erosion and conservation in Yunnan Province, China

The scale and severity of soil erosion within the headwaters of the Yangtze River in Yunnan Province are discussed. The Yangtze River rises in the wes tern uplands of the Qinghai-Tibet Plateau and traverses 6380 km through sou thern and central China. The headwaters are in tectonically active and geol ogically unstable uplands. The basin is also generally under intensive agri cultural use, mainly for rice cultivation. Hence, erosion rates are high an d of increasing concern, especially considering the construction of the Thr ee Gorges (Sanxia) Dam in the middle section. Sedimentation within the prop osed reservoir could impair its efficiency and therefore soil conservation must be an integral component of basin management. Soil conservation effort s in Yunnan are reviewed and the local-scale planned approach to soil conse rvation is illustrated, using Dongchuan and Xundian as case studies. An ong oing runoff plot study at Yunnan Agricultural University (Kunming) is used to evaluate the effectiveness of various soil conservation measures. Maize (Zea mays) cropping treatments, typically employed in local agronomic pract ices, are applied to 30 erosion plots at 3 different slope angles, cultivat ed both parallel and perpendicular to the contour, thus simulating a range of agricultural conditions on arable slopes. Plot data from 1993-1996 sugge st several suitable soil conservation measures. Erosion rates were generall y lower on plots where contour cultivation was used. The mean contour culti vation erosion rate was 0.69 of the mean downslope orientated cultivation r ate. Straw mulch and contour cultivation seem particularly suitable soil co nservation measures.