Ammonia mitigation campaign with smallholder farmers improves air quality while ensuring high cereal production

Reducing cropland ammonia (NH3) emissions while improving air quality and food supply is a challenge, particularly in China with millions of smallholder farmers. We tested the effectiveness of a tailored nitrogen (N) management strategy applied to wheat-maize cropping systems in “Demonstration Squares” across Quzhou county in North China Plain. The N management techniques included optimal N rates, deep fertilizer placement and application of urease inhibitors, implemented through cooperation between government, researchers, businesses and smallholders. Compared with conventional local smallholder practice, our NH3 mitigation campaign reduced NH3 volatilization from wheat and maize by 49% and 39%, and increased N use efficiency by 28% and 40% and farmers’ profitability by 25% and 19%, respectively, with no detriment to crop yields. County-wide atmospheric NH3 and PM2.5 concentrations decreased by 40% and 8%, respectively. County-wide net benefits were estimated at $7.0 million. Our “Demonstration Square” approach demonstrates that cropland NH3 mitigation and improved air quality and farm profitability can be achieved simultaneously by coordinated actions at county level.