Physiological indicators drive climate-smart and sustainable AWD irrigation in rice systems

Efficient water management is crucial for modern rice cultivation, particularly in the context of climate change and limited water resources. To optimize irrigation, this study evaluated the physiological responses of rice to water stress. From January to April 2022, a randomized complete block design (RCBD) was employed to evaluate physiological traits associated with water regulation in rice plants. Key photosynthetic metrics, including stomatal conductance (g_sw), leaf temperature (T_leaf), fluorescence (F_s), electron transport rate (ETR), and photosystem II efficiency (Φ_PSII), as well as stress markers such as malondialdehyde (MDA) content and osmolality, were monitored. Results showed that g_sw shifts preceded visible stress symptoms, making them reliable early indicators of irrigation need. In the second experiment, water-use efficiency, plant stress, and greenhouse gas (GHG) emissions were measured from October 2022 to February 2023 to refine alternative wetting and drying (AWD) methods for better water-use efficiency. Using g_sw thresholds, the modified AWD (mAWD) outperformed conventional AWD (cAWD) in terms of irrigation water productivity (WP_I) and consumptive water footprint (WF_consumption) without inducing stress conditions in rice. WP_I for continuous flooding (CF), cAWD, mAWD was 1.16, 2.72 and 3.92 kg m^-3, while WF_consumption was 1,079.93, 584.90 and 517.57 m³ t^-1, respectively. Additionally, mAWD reduced yield-scaled GHG emissions, enhancing environmental benefits. This study underscores the value of physiological monitoring, especially g_sw, to advance AWD irrigation for sustainable rice production.