Significant reduction of ammonia emissions while increasing crop yields using the 4R nutrient stewardship in an intensive cropping system

Ammonia (NH3) emissions should be mitigated to improve environmental quality. Croplands are one of the largest NH3 sources, they must be managed properly to reduce their emissions while achieving the target yields. Herein, we report the NH3 emissions, crop yield and changes in soil fertility in a long-term trial with various fertilization regimes, to explore whether NH3 emissions can be significantly reduced using the 4R nutrient stewardship (4Rs), and its interaction with the organic amendments (i.e., manure and straw) in a wheat–maize rotation. Implementing the 4Rs significantly reduced NH3 emissions to 6 kg N ha–1 yr–1 and the emission factor to 1.72%, without compromising grain yield (12.37 Mg ha–1 yr–1) and soil fertility (soil organic carbon of 7.58 g kg–1) compared to the conventional chemical N management. When using the 4R plus manure, NH3 emissions (7 kg N ha–1 yr–1) and the emission factor (1.74%) were as low as 4Rs, and grain yield and soil organic carbon increased to 14.79 Mg ha–1 yr–1 and 10.09 g kg–1, respectively. Partial manure substitution not only significantly reduced NH3 emissions but also increased crop yields and improved soil fertility, compared to conventional chemical N management. Straw return exerted a minor effect on NH3 emissions. These results highlight that 4R plus manure, which couples nitrogen and carbon management can help achieve both high yields and low environmental costs.