Soil erosion and conservation in the headwaters of the Yangtze River, Yunnan Province, China

In the headwaters of the Yangtze River, erosion rates are high and of increasing concern, not least because of the construction of the Three Gorges (Sanxia) Dam downstream. Sedimentation within the proposed reservoir could impair its efficiency and therefore soil conservation must be an integral component of basin management. Soil conservation efforts in Yunnan are reviewed and the local-scale planned approach is illustrated, using Dongchuan and Xundian as case studies. A runoff plot study at Yunnan Agricultural University (Kunming) is evaluating the effectiveness of various soil conservation measures. Maize (Zea mays) cropping treatments, typically employed in local agronomic practices, are applied to 30 erosion plots at three different slope angles, cultivated both parallel and perpendicular to the contour, thus simulating a range of agricultural conditions on arable slopes. Plot data from 1993-96 suggest several suitable soil conservation measures. The average rank order of treatment effectiveness, in diminishing erosion rates, was: 1 straw mulch, 2 intercropping, 3 no tillage, 4 polythene mulch and 5 conventional tillage. The mean erosion rate on the straw mulch plots was 0.22 of the mean conventional tillage rate. Erosion rates, were generally lower on plots where contour cultivation was used. The mean contour cultivation erosion rate was 0.69 of the mean do downslope-orientated cultivation rate. Therefore, straw mulch and contour cultivation seem particularly suitable soil conservation measures. Currently, the research team is attempting to extrapolate conservation treatments validated in plot experiments to actual field conditions.