Water use of rice and mung bean cultivations in a downstream area of an irrigation system in South Sulawesi in the 2nd dry season

This paper revealed the irrigation rate by groundwater, evapotranspiration (ET), total water balance and yield in the experimental rice and mung bean fields in a downstream of an irrigation system in South Sulawesi in the 2nd dry season. In the rice field, the irrigation rate was 2678.4 mm by 21 times intermittent irrigation, the effective rainfall was 77.1 mm and ET was 539.1 mm, totally. The water balance suggested that 81% of input water should have been consumed by vertical percolation, lateral seepage and surface runoff through the levee and infiltration in temporal earth ditches during conveying pumped water. To decrease such losses of irrigated water, more frequent but smaller irrigation to keep the soil surface saturated without forming cracks and the farm-lot consolidation of rice fields was proposed as one of prospective ways. In the mung bean field, the irrigation rate was 163.3 mm just by twice irrigation, rainfall was 118.2 mm and ET was 320.3 mm, totally. The water balance suggested that mung bean could make the deficit up by absorbing moisture from the deeper soil layer and groundwater through deeply extended roots. Additional possible supply was by the lateral seepage and runoff from an adjacent rice field. The yield of mung bean was one-third of the national average. To increase the yield, more frequent irrigation was required. But alternatively, cultivation of other crops, which have higher commodity values and are tolerant to the dry condition, was also proposed as one of prospective ways.