Weather-dependent effects of Alternate Wetting and Drying (AWD) irrigation on ratoon rice: a 3-year field study

Alternate wetting and drying (AWD) irrigation improves water use efficiency (WUE) in rice, but its effectiveness in ratoon rice under varying climatic conditions remains unclear. This study is the first 3-year field experiment to assess the climate-dependent impacts of AWD irrigation on ratoon rice, particularly under extreme heat conditions.

A 3-year field experiment (2020-2022) was conducted to examine AWD irrigation's effects on soil properties, rice growth, yield, and WUE in a main-season-ratoon rice system. Four irrigation methods were tested: conventional irrigation (CK), AWD during the main-season rice filling period (T1), AWD during the ratoon rice filling period (T2), and AWD during both periods (T3). Weather data showed higher temperatures and lower rainfall in 2022 compared to 2020 and 2021.

AWD irrigation increased soil bulk density and total nitrogen, and and NO3- concentrations, while reducing NH4+ concentrations in both rice seasons. In 2020 and 2021, AWD irrigation positively increased root dry weight and activity, net photosynthetic rate, chlorophyll fluorescence, nitrogen metabolism enzyme activity, yield and WUE. However, the opposite was observed in 2022. Specifically, in 2020 and 2021, compared with CK, T1 and T3 increased the yield in the main season by 12.81% and 11.66%; T1, T2 and T3 increased the yield in the ratoon season by 12.93%, 7.66% and 24.10%; T1 and T3 increased the WUE in the main season by 14.90% and 14.07%; and T1, T2 and T3 increased the WUE in the ratoon season by 11.10%, 15.01% and 33.00%, respectively. In 2022, compared with CK, T1 and T3 reduced the yield in the main season by 12.04% and 12.60% and the yield in the ratoon season by 13.72% and 16.37%, and T1 and T3 reduced the WUE in the main season by 10.34% and 10.35% and the WUE in the ratoon season by 3.45% and 10.34%, respectively.

AWD irrigation enhances yield and WUE under normal conditions but reduces them under extreme heat. This study highlights the need for adaptive irrigation strategies, integrating heat-tolerance measures to counteract the adverse effects of climate change on ratoon rice production.