Role of Organic and Conservation Agriculture in Ammonia Emissions and Crop Productivity in China.

There is an increasing food demand with growing population and limited land for agriculture. Conventional agriculture with nitrogen (N) fertilizer applications, however, is a key source of ammonia (NH 3 ) emissions that cause severe haze pollution and impair human health. Organic and conservation agricultural (OCA) practices are thereby recommended to address these dual challenges; however, whether OCA provides cobenefits for both air quality and crop productivity is controversial. Here, we perform a meta-analysis and machine learning algorithm with data from China, a global hotspot for agricultural NH 3 emissions, to quantify the effects of OCA on NH 3 emissions, crop yields and nitrogen use efficiency (NUE). We find that the effects of OCA depend on soil and climate conditions, and the 40-60% substitution of synthetic fertilizers with livestock manure achieves the maximum cobenefits of enhanced crop production and reduced NH 3 emissions. Model forecasts further suggest that the appropriate application of livestock manure, straw return, and no-till could increase grain production up to 59.7 million metric tons (100% of straw return) and reduce maximum US$2.7 billion (60% substitution with livestock manure) in damage costs to human health from NH 3 emissions by 2030. Our findings provide data-driven pathways and options for achieving multiple sustainable development goals and improving food systems and air quality in China.