Effects of cultivation techniques on maize productivity and soil properties on hillslopes in Yunnan Province, China
The rapid population increase in China from 556.7 to 1226.7 million during the past 50 years means China has one-sixth of the world’s population. This population growth has imposed high pressures on Chinese agriculture. Crop production and productivities have more than doubled, for example mean maize yields have increased from 1.54 to 3.91 t ha-1 from 1960 to 1998. Despite this, food shortages remain major problems. These pressures have also led to intensive cultivation of sloping lands, making China the country with the most serious soil erosion problems in the world. Yunnan Province, south-west China, has some 70% of its total of 6.53 million hectares of cultivated fields located on sloping land, most of which suffers from soil erosion. Furthermore, traditional downslope cultivation of these upland fields produces increased soil loss and runoff and threatens agricultural sustainability. Crop yields on sloping land in these areas have decreased by 30-60% in the last century because of soil erosion and in 50-100 years most topsoil may have been removed. There is an urgent need to develop more productive and sustainable cropping systems and the dual aims of this project were to investigate ways of increasing productivity of maize on sloping land, while conserving soils. This investigation was carried out in Wang Jia Catchment (25028’N,102053’E), selected as a representative area of fragile slopes in Yunnan Province. Five treatments (1) Traditional + Downslope planting (control), (2) Traditional + Contour planting, (3) Traditional + Contour + Straw mulch, (4) Minimum tillage + Contour + Straw mulch and (5) Traditional + Contour + Polythene mulch, were selected for evaluation and established on replicated field plots in 1998 and 1999. An additional experiment in 1999 investigated the effects of irrigation on crop yield. Although there were variations during the growing season and between years, straw mulch with contour planting increased soil moisture (0-20 cm depth) and was associated with lower soil temperatures. Polythene mulch improved soil moisture retention when applied after early season rainfall or irrigation and caused increases in soil surface temperature of up to 4-50C. These increases in soil moisture and temperature were associated with increases in Green Leaf Area Index, Green Leaf Area Duration and standing biomass. Grain yield was increased up to 51.6%, compared to un-mulched plots. Straw mulch increases in yield 14.0 and 20.7% (nonirrigated treatment), compared with the control in 1998 (5.0 versus 4.3 t ha-1) and 1999 (6.2 versus 5.3 t ha-1), respectively. Furthermore, straw mulch appeared to be beneficial for maintaining soil fertility and improving soil structure. Irrigation improved early vegetative growth and final yields when early season rainfall was unreliable and maize grain yield increased by 39.5 to 59.6% in 1999, compared with the corresponding non-irrigated treatments. Polythene mulch and contour planting combined with early irrigation produced the highest maize yields. The results are compared with other published work, including research in erosion plots, where the effectiveness of mulches in reducing runoff and erosion has been evaluated. A cultivation technique combining polythene mulch, straw mulch, contour planting and early season irrigation is considered likely to be highly effective for increasing productivity and improving soil conservation on sloping land. This project is part of a larger programme, which aims to establish and evaluate a demonstration model at a catchment scale for more sustainable crop production systems in the highlands of South-East Asia.