Safeguarding Food Supply and Groundwater Safety for Maize Production in China.

Quantifying sustainable nitrogen (N) management at the national scale is critical for developing targeted policies and strategies to simultaneously achieve food security and groundwater protection. In this study, we report county-scale optimization scenarios for Chinese maize production and evaluate their outcomes for safeguarding food supply and groundwater safety. First, we performed random forest regression modeling to simulate NO leaching based on a meta-analysis that integrates climate, soil, water, and N balance parameters. The NO leaching was then mapped for 1406 counties based on data compiled from 2.89 million farmer surveys. Average NO leaching during the maize growth season was estimated to be 27.6 kg N ha, and 56% of counties had groundwater whose nitrate concentrations exceeded drinking water safety levels during 2005-2014. The top 5% farmers in each county produced not only more grain but also greater NO leaching. Scenario analysis of potential management changes found that when these top producers combined optimal N management practices, national N use in Chinese maize system was reduced by 25%, from 9.1 to 6.9 Mt, while maize production increased by 6.1%. Modeled NO leaching was 0.58 Mt, which was 31% lower than groundwater safety levels and 53% lower than the current leaching amount. This study provides evidence that integrated crop and N management practices implemented at the county level safeguard both maize crop food security and enhance environment sustainability.