Soil erosion in Yunnan Province, southwest China, is recognised as a major environmental problem. With some 95% of the Province classed as mountainous and the valleys and plains already fully utilised for agriculture, industry and urban growth, pressure on remaining land resources is high. Cultivation has steadily encroached onto increasingly steep and marginal land, which further accelerates erosion rates. Little published work is available of soil erosion rates or potential soil conservation measures in Yunnan. A collaborative research programme was initiated between Yunnan Agricultural University (YAU) and The University of Wolverhampton to study several potential soil conservation measures. Thirty runoff plots on the experimental farm of YAU were used to investigate the effectiveness of five treatments: conventional tillage (control), no-tillage, straw mulch, polythene mulch and intercropping. Plots were cropped with maize (Zea mays) sown either along the contour or downslope, on 3, 10 and 27 slopes. Data on erosion rates and crop productivity were collected during four growing seasons (May-October), 1993-1996 inclusive. Seasonal rainfall totals were 576.3, 768.3, 876.3 and 619.7 mm in 1993, 1994, 1995 and 1996, respectively. Respective seasonal mean erosion rates equalled 0.73, 4.00, 7.56 and 0.05 tha(-1). Straw mulch was very effective in decreasing erosion rates. In 1993, 1994, 1995 and 1996, soil loss was 18, 66, 86 and 78% less than the conventionally tilled plots, respectively. Straw mulch maintained topsoil structure and encouraged infiltration, thus decreasing runoff and erosion rates. Conversely, erosion rates under conventional tillage were high. Erosion rates from the polythene mulch plots were similar to conventional tillage, as infiltration was effectively decreased, thereby concentrating runoff and channelling it towards exposed, inter-mulch areas. However, maize development and grain yields were consistently higher under the polythene mulch than the other treatments. Mean contour cultivation erosion rates were 31% less than downslope planting rates. The collaborative research on soil conservation is continuing, with a catchment-based research programme underway in Wang Jia catchment in Kedu Township, in northeast Yunnan. (C) 2004 Elsevier B.V. All rights reserved.
