Cassava production practices in Asia-Can they maintain soil productivity

Cassava production practices in Asia vary greatly, depending mainly on farm size, labor availability, soil and climate, socio-economic conditions and local traditions. On larger farms in Asia, especially in Thailand, Malaysia, Mindanao island (Philippines) and Hainan island (China), cassava is grown in monoculture. In Guangdong and Guangxi provinces of China, in parts of Vietnam, the Philippines, and especially in Indonesia, cassava is normally intercropped with peanut, maize, upland rice, soybean, mungbean or watermelon. Cassava is usually grown continuously on the same fields year after year, but in some areas the crop is rotated with maize, sugarcane or bush fallow to prevent a decline in soil fertility. In China, Vietnam, India and Indonesia, soil productivity is usually improved through the use of pig or cow manure, sometimes augmented with wood ash or chemical fertilizers. Fertilizer use is increasing among farmers in Thailand, albeit at low application rates, while in Malaysia application rates are quite high. Maintaining soil fertility in cassava fields depends largely on the rates at which manure and chemical fertilizers are used, and whether the nitrogen, phosphorus and potassium (N, P and K) applications correspond with the local soil characteristics and crop requirements. In most Asian countries, fertilizer recommendations are not based on soil analyses, often leading to the application of excessive amounts of P and inadequate amounts of K. While cassava in Asia is seldom grown on very steep slopes (except in parts of China, Indonesia and Vietnam), even on gentle slopes the crop can cause severe erosion when grown on light-textured soils with low levels of organic matter. Erosion-induced soil losses of over 100 t/ha/year have been recorded in trials conducted in Hainan island (China), Leyte island (Philippines) and East Java (Indonesia). Research has shown that erosion can be reduced markedly by simple agronomic practices, such as application of fertilizers, zero or reduced tillage, closer plant spacing, mulching, intercropping, or the planting of contour barriers of various grasses, legumes or fast-growing tree species. However, few of these practices are currently used by cassava farmers. By involving farmers directly in the testing and selection of soil conservation practices on their own land, more suitable practices may be developed, and hopefully this will lead to increased adoption of management practices that not only increase cassava yields but also maintain the soil productivity.