Utilizing rainfall and alternate wetting and drying irrigation for high water productivity in irrigated lowland paddy rice in southern Taiwan

Taiwan's average annual rainfall is high compared to other countries around the world; however, it is considered a country with great demand for water resources. Rainfall along with alternate wetting and drying irrigation is proposed to minimize water demand and maximize water productivity for lowland paddy rice cultivation in southern Taiwan. A field experiment was conducted to determine the most suitable ponded water depth for enhancing water saving in paddy rice irrigation. Different ponded water depths treatments (T 2 cm , T 3 cm , T 4 cm and T 5 cm ) were applied weekly from transplanting to early heading using a complete randomized block design with four replications. The highest rainwater productivity (2.07 kg/m 3 ) was achieved in T 5 cm and the lowest in T 2 cm (1.62 kg/m 3 ). The highest total water productivity, (0.75 kg/m 3 ) and irrigation water productivity (1.40 kg/m 3 ) was achieved in T 2 cm . The total amount of water saved in T 4 cm , T 3 cm and T 2 cm was 20, 40, and 60%, respectively. Weekly application of T 4 cm ponded water depth from transplanting to heading produced the lowest yield reduction (1.57%) and grain production loss (0.06 kg) having no significant impact on yield loss compared to T 5 cm . Thus, we assert that the weekly application of T 4 cm along with rainfall produced the best results for reducing lowland paddy rice irrigation water use and matching the required crop water.