Optimizing the lateral dripline spacing of drip-irrigated aerobic rice to increase water productivity and profitability under the water-limited condition

Abstract

The potential use of drip irrigation to reduce water use without yield penalty in aerobic rice cultivation has not been fully explored in the tropics due to high investment costs. One major way to lowering this cost is by optimizing the lateral spacing to serve more rows of rice plants per dripline. This study evaluates the effects of lateral dripline spacing on the grain yield, water productivity, and the economic return in aerobic rice production. Field experiments were conducted for the period of two years (2020–2021) using three lateral dripline spacings (40-cm, 60-cm, and 80-cm) as treatments and surface flooding as the control. Grain yields, water use, water productivity, and economic benefits were evaluated. The drip-irrigated aerobic rice did not show significant differences with surface flooding except for a lower yield at 80-cm in 2021 dry season due to its low percent filled grains. Among treatments, the 60-cm lateral spacing consistently obtained the highest irrigation water productivity by up to 1.03 kg m-3 and 42% irrigation water savings relative to surface flooding. Increasing the spacing of the lateral dripline decreased the material costs (80 <60 <40 cm) by 10–36%. The 60-cm spacing produced the highest average net income by 41–75% among drip treatments and had comparative economic returns compared with surface flooding. The net present value and the benefit-cost ratio indicate that it is economically viable to invest in drip irrigation using a 60-cm lateral spacing. Thus, this study suggests that when there is insufficient water to grow surface flooding aerobic rice, drip irrigation using 60-cm lateral spacing is the best option for reducing irrigation water use and increasing water productivity; while having comparative yield and economic return as surface flooding method of aerobic rice cultivation.