Modeling the impacts of water and fertilizer management on the ecosystem service of rice rotated cropping systems in China

Detailed information on the impacts of water use and nutrient application on agro-ecosystem services including crop yields, greenhouse gas (GHG) emissions and nitrogen (N) loss is the key to guide field managements. In this study, we use the DeNitrification-DeComposition (DNDC) model to simulate the biogeochemical processes for rice rotated cropping systems in China. We set varied scenarios of water use in more than 1600 counties, and derived optimal rates of N application for each county in accordance to water use scenarios. Our results suggest that 0.88 ± 0.33 Tg per year (mean ± standard deviation) of synthetic N could be reduced without reducing rice yields, which accounts for 15.7 ± 5.9% of the N application in China in 2005. Field managements with shallow flooding and optimal N applications could enhance ecosystem services at a national scale, leading to 34.3% reduction of GHG emissions (CH4, N2O, and CO2), 2.8% reduction of overall N loss (NH3 volatilization, denitrification and N leaching) and 1.7% increase of rice yields, as compared to current management conditions. Among provinces with major rice production, Jiangsu, Yunnan, Guizhou, and Hubei could achieve more than 40% reduction of GHG emissions under appropriate water managements, while Zhejiang, Guangdong, and Fujian could reduce more than 30% N loss with optimal N applications. Our modeling efforts suggest that China is likely to benefit from reforming water and fertilization managements for rice rotated cropping systems in terms of sustainable crop yields, GHG emission mitigation and N loss reduction, and the reformation should be prioritized in the above-mentioned provinces.