Multi-objective water management strengthens synergistic control of nitrogen and phosphorus losses and CH4 emissions in paddies in the Yangtze River Basin.

Abstract

Synergistically mitigating non-point source (NPS) pollution and greenhouse gas (GHG) emissions remains a challenge in rice production, due to "trade-off" emission effects. This study proposed the new multiple-objective irrigation (MOI) strategy with improved water management based on differences of critical periods (CPs) of total nitrogen (TN) and total phosphorus (TP) losses and methane (CH₄) emissions. Through a systematic analysis of multi-sites data from 148 studies, CPs for single TN and TP losses, single CH₄ emissions, and coupled carbon-nitrogen-phosphorus loss were identified as: the turning green stage, the mid to late tillering stages, and the early tillering to early jointing-booting stages, respectively. Based on these identified periods, three water management strategies - "as much storage as possible", "as much drainage as possible", and "low-water management" - were applied in the MOI, incorporating distinct water thresholds, specific durations for field drying, and water retention parameters. Field experiment revealed that MOI significantly outperformed traditional flooding irrigation (TFI) and alternate wetting and drying (AWD) practices in water-saving and pollution mitigation. MOI reduced 35.65 % and 29.21 % TN losses, 64.31 % and 54.34 % TP losses, and 66.46 % and 43.28 % CH₄ emissions compared to TFI and AWD, respectively. Moreover, MOI conserved 56.76 % and 48.39 % irrigation water compared to TFI and AWD, respectively, while exhibiting better tolerance to high-temperature stress relative to AWD and maintaining stable yields. This study confirmed that accurate identification of CPs and optimization of irrigation can synergistically enhance agricultural production and ecological benefits, providing a significant basis for sustainable water management in paddy fields.