MUNGBEAN RESPONSE TO SURFACE DRAINAGE WHEN GROWN AS A PRE-RICE CROP ON WATERLOG-PRONE RICELANDS

Large areas of the world's bunded rainfed lowland ricelands could be p lanted to a pre-rice crop if waterlogging damage during the early wet season is prevented. To build understanding necessary to develop effec tive field drainage practices for pre-rice crops, pot and field studie s were undertaken on a Typic Tropaquept lowland rice soil in the Cagay an Valley, Philippines. The objective of the studies was to quantify e ffects of excessive moisture on mungbeans (Vigna radiata (L,) Wilczek) encountering variable regimes of duration and elevation of water tabl e height in the root zone during a short-term waterlogging event. Smal l differences in level and duration of the root zone water table marke dly affected plant performance. Yields were reduced by 40-100% when th e water table level reached the soil surface for 6 days compared with the unstressed treatment, but were reduced by only 12-17% when the wat er level was 5 cm below the surface for the same time period. Regressi on analysis revealed a 4% reduction in yield per centimetre increase i n water table level between 5 cm below to 5 cm above the soil surface during the vegetative stage, and a 6.5% reduction per centimetre durin g the reproductive stage. Field experiments evaluated two prospective surface drainage techniques that farmers could employ to elevate the c rop above the zone of saturation during waterlogging events. Planting in furrows, and subsequently hilling up (HU) to create ridges was unsu ccessful in improving plant performance (as the base of the plant was not elevated). Planting on 25 cm high ridges formed by a plow dramatic ally improved growth and yield of mungbean (greater than or equal to 3 60% advantage compared with the other treatments) when subjected to a range of waterlogging stress events, Standing water occurred for 5-7 d ays on the soil surface of HU, broadcast seeded (B), and drilled (D) t reatments, but was 5-6 cm below the base of the plants in the ridge tr eatment during the two flooding events. The ridging method was observe d to be effective for farm-scale use in cultivating pre-rice mungbeans with either animal or tractor power.