A moderate wetting and drying regime produces more and healthier rice food with less environmental risk

Context and problem: Water management is one of the most important practices to determine rice yield, water use efficiency (WUE), uptake of arsenic (As) and cadmium (Cd) by plants, and greenhouse gas (GHG) emissions from the paddy field. However, few studies measured all of these outcomes simultaneously at a whole system level. Objective: The objective of this study was to test the hypothesis that an alternate wetting and moderate drying regime (WMD) could achieve multiple goals of increasing rice yield, saving water, and reducing As and Cd contents in the grain and GHG emissions from the paddy field, either with or without wheat straw incorporation. Methods: A high-yielding rice variety was grown in the field and three irrigation regimes were conducted including conventional irrigation (CI), WMD, and alternate wetting and severe drying (WSD), either with wheat straw incorporation (+WS) or without wheat straw incorporation (-WS) in each regime. In CI regimes, the field was continuously flooded except drainage in the mid-season. In WMD and WSD regimes, fields were not irrigated until the soil water potential reached -15 kPa and -30 kPa at 15-20 cm depth of the soil, respectively. Results: Compared with CI regimes, WMD regimes significantly increased grain yield by 6.18-8.15 % in-WS plots and by10.1-11.1 % in +WS plots, whereas WSD regimes markedly decreased it, with less reduction in the +WS plots. The WMD regimes increased available nitrogen and microbial biomass carbon contents in the soil. Both WMD and WSD regimes pronouncedly increased water use efficiency and decreased As content in the grain. The WMD decreased, while the WSD increased, Cd content in the grain. Either WMD or WSD substantially reduced CH4 emissions and increased N2O emissions from the field. However, the reduction in CH4 emissions far over-weighed the increases in N2O emissions in CO2 eq in both regimes. The emission of CO2 was increased in WSD regimes, whereas it showed no significant difference between WMD and CI regimes. The WMD regimes signif-icantly decreased global warming potential and yield-scaled global warming potential in either -WS or +WS plots. Conclusions: A WMD regime could produce more and healthier rice food with less environmental risk. Implications: This study provides useful information for rice production to produce more and healthier food and reduce environmental risk by improving water management.

Automated summary

Water management plays a crucial role in determining rice yield, water use efficiency, uptake of arsenic and cadmium by plants, and greenhouse gas emissions in paddy fields. This study aimed to test the hypothesis that an alternate wetting and moderate drying regime could achieve multiple goals of increasing rice yield, saving water, and reducing harmful elements and greenhouse gas emissions. The results showed that this water management regime effectively increased rice yield, improved water use efficiency, reduced arsenic content, and decreased greenhouse gas emissions.