Crop diversification in lowland rice cropping systems in Cambodia: effect of soil type on legume production.

he majority of rice production in Cambodia is based on rainfed lowland cropping systems, where rice is grown over the wet season, and fields left fallow over the dry season. Improved rice production systems in Cambodia have provided opportunities for crop diversification in rainfed lowland cropping areas. We aim to develop a system based on rice production in the wet season, followed by legume crops grown in the dry season, to provide farmer income over a greater portion of the year. In 2007-08, we evaluated peanut, soybean and mungbean production on 4 soil types commonly used for lowland rice production in Cambodia. Establishment and growth of legume crops varied between varieties and sites. Poor crop establishment and growth was attributed to soil physical constraints, and compounded by differences in crop management between sites. Inherent soil acidity and poor soil structure as a result of wet cultivation for preceding rice production, impaired nutrient availability and uptake by the crop. Insect pests, diseases and weeds also contributed to reductions in yield. Water management was also a significant issue in this rice/legume rotation system. Agronomic and management strategies need to be developed to minimise these constraints. There is potential for adoption of practices such as minimum tillage, retention of crop residues, raised bed configuration, irrigation strategies, and inoculation of legume seed, to improve production in this Cambodian system. Experiments to examine the effect of these treatments on legume crop production on lowland rice soils will be implemented in the 2008-09 dry season.