A theoretical study for North Vietnam of alternative agroforestry systems to pure cassava

Cassava is recognized in the region as the second most important crop after paddy rice. In Vinh Phu province of Vietnam, it is usually grown on highly erodible slopes of the small hills surrounding paddy fields. Cassava crop land is generally in annual use until the yield is less than 3–4 t fresh tubers/ha. This constant cropping system rapidly depletes the soil as fertilizers are infrequently used and crop residues are usually removed from the fields. Erosion is a major problem as the soil is exposed through hand cultivation and regular weeding during a cropping season which coincides with the wet season. Sustainable and productive cropping systems are needed.In order to take a first step towards sustainability, this paper presents several possible agroforestry systems in which cassava could be intercropped with a number of nitrogen fixing trees and shrubs. Several theoretical combinations have been examined assuming a critical lower production limit of 3–4 t fresh tubers/ha. Those with sustained high potential yields are recommended for future field experimentation.