Alternate wetting and drying in high yielding direct-seeded rice systems accomplishes multiple environmental and agronomic objectives

Rice (Oryza sativa L.) cultivation is critically important for global food security, yet it also represents a significant fraction of agricultural greenhouse gas (GHG) emissions and water resource use. Alternate wetting and drying (AWD) of rice fields has been shown to reduce both methane (CH4) emissions and water use, but its effect on grain yield is variable. In this three-year study we measured CH4 and nitrous oxide (N2O) emissions, rice grain total arsenic (As) concentrations, yield response to N rate, and grain yield from two AWD treatments (drill-seeded and water-seeded) and a conventionally managed waterseeded treatment (control). Grain yields (average = 10 Mg ha ) were similar or higher in the AWD treatments compared to the control and required similar or lower N rates to achieve these yields. Furthermore, AWD reduced growing season CH4 emissions by 60–87% while maintaining low annual N2O emissions (average = 0.38 kg N2O–N ha ); N2O emissions accounted for <15% of the annual global warming potential (GWP) in all treatments. Fallow season emissions did not vary by treatment and accounted for 22–53% of annual CH4 emissions and approximately one third of annual GWP on average. The AWD treatments reduced annual GWP by 57–74% and growing season yield-scaled GWP by 59–88%. Milled grain total As, which averaged 0.114 mg kg 1 in the control, was reduced by 59–65% in the AWD treatments. These results show that AWD has the potential to mitigate GHG emissions associated with rice cultivation and reduce rice grain total As concentrations without sacrificing grain yield or requiring higher N inputs; however future research needs to focus on adapting AWD to field scales if adoption of this technology is to be realized. ã 2016 Elsevier B.V. All rights reserved.