| Summary: | Efficient management of freshwater resources is critical as threats to water security increase due to changes in climate, population, and land use. The water and agricultural sectors of Asian countries have been identified as the most at risk for climate change impacts, and small-scale farmers are particularly vulnerable to changes in water availability and water quality. This research explored the tradeoffs between maximization of yield and minimization of environmental impact in rice production in Sri Lanka. The study used the DeNitrification-DeComposition (DNDC) model to examine how variations in climate, soil, and paddy management affect outputs of yield, greenhouse gas (GHG) emissions, and nitrogen (N) leaching in paddy systems in Sri Lanka from 1991 to 2010. Reducing fertilizer had little effect on yield, and N leaching and N2O emissions declined as a result. Reliable water inputs in irrigated systems increased yields over rain-fed schemes; alternate flooding techniques to mitigate water stress did not reduce yield. Alternate flooding increased N leaching as did rain-fed cultivation. A sensitivity analysis of soil parameters determined that high clay content reduced N leaching, low soil organic carbon increased yield, and the more basic the pH of the soil, the greater the reduction in GHG emissions. The results inform best practices for Sri Lankan farmers and decision makers on the supervision of water resources and agricultural inputs. This research demonstrates how cultivation in rice-growing regions in south Asia affects the environment and the nitrogen cycle on a global scale, in turn how informed management of these systems can adapt to a changing environment.
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