Development of sustainable legume production in rice-based farming systems in Cambodia

Lowland rice production is the dominant agricultural enterprise in Cambodia, traditionally grown as a single crop over the wet season, with land remaining fallow over the dry season. Development of a farming system where legumes are produced in the dry season following wet season rice, poses numerous constraints. These include: poor soil quality characteristic of lowland rice soils, provision and maintenance of adequate soil moisture over the dry season, and management of a novel crop for traditional rice farmers. A series of experiments were conducted from 2007 to 2010 to evaluate a number of production variables on two legume crops, mungbean and peanut, sown post-wet season rice. In lighter soils where legumes appear suitable for growth, soil-stored water from the wet season is not sufficient to grow legume crops, and supplementary irrigation water is required. Comparison between three bed configurations using gravity fed irrigation, and the traditional watering can method, found that flood irrigation on flat beds could improve yields, and farmers preferred this method over the labour intensive hand-watering method, although water use increased. Use of rice straw as mulch reduced weed growth and promoted legume growth, and increased water use efficiency. Future work will need to determine the most efficient bed configuration to facilitate irrigation and to optimise plant population, and to evaluate specific irrigation scheduling on the amount and timing of water required, in different soil types for more sustainable rice based dry season legume farming systems.