Estimation of potential area of preparatory irrigation for rainy season lowland rice and supplemental irrigation for dry season cropping using existing reservoirs constructed for aquaculture: a case study in semi-mountainous village, Lao PDR

Abstract

The rural area in Lao PDR has a low yield of rainy season lowland rice, and most rice fields are not utilized for crop cultivation during the dry season. Delay in transplanting owing to late field ponding is considered the cause for the low yield of rainy season lowland rice. Reservoirs for aquaculture are located in the upper part of fields; however, stored water is not efficiently utilized. In this study, a potential area of preparatory irrigation for early field ponding (APIR) and supplemental irrigation for dry season cropping (ASID), using existing reservoirs, was estimated in two basins in the semi-mountainous village of Lao PDR. Estimated water withdrawal was calculated considering water balance in four cases of water management in reservoirs, considering aquaculture cultivation period and timing of the drainage operation. Water requirements for early field ponding and soybean, a candidate crop for dry season cropping, and conveyance efficiency were calculated using hydrological approaches. Results show APIR in each basin was 4.1 ha and 8.6 ha under current water management in a low-yield rice field area of 7.8 ha and 6.3 ha, respectively. ASID in each basin was 2.1 ha and 1.1 ha, respectively, under current water management. Although APIR and ASID increased under closed aquaculture, the impact was negligible. ASID increased when the drainage operation shifted to the final timing of supplemental irrigation. This water management approach was recommended for both types of irrigation considering improved agricultural productivity obtained through more efficient use of stored water, with aquaculture maintained.