Evaluating water depths for high water productivity in irrigated lowland rice field by employing alternate wetting and drying technique under tropical climate conditions,Southern Taiwan

The uncertainty of monsoon rainfall and the decreasing availability of irrigation water, as a result of climate change, and high water demand of other sectors have resulted to wide adoption of alternate wetting and drying (AWD) technique especially in irrigated lowland rice production to overcome water scarcity. However, under climate change circumstances, AWD can be optimized when taking advantage of favorable water seasonality conditions to increase crop yield and irrigation water use efficiency. Therefore, a field trial was conducted to find suitable water depth for reducing rice irrigation water use by combining four different water depth treatments (T_2cm, T_3cm, T_4cm, and T_5cm) with rainfall through a randomized complete block design having 3 replications. Water depths were applied weekly from transplanting to heading. The results showed that water stress at vegetative stage decreased plant height and tillers number between 7 and 33 % at panicle initiation, followed by total and partial growth recovery. In addition, panicle number per hill showed a 53–180 % decrease at the heading stage. Severe water stress induced by the lowest water treatment significantly reduced yield components between 15 and 52 % at harvest. It was found that weekly application of 3 cm water depth combined with rainfall improved AWD effectiveness, and yielded the highest beneficial water productivity with less yield expenses.