Straw return reduces yield-scaled N2O plus NO emissions from annual winter wheat-based cropping systems in the North China Plain.

Straw return in combination with synthetic N fertilizer is considered to be beneficial to soil fertility and crop yield. Such practice, however, can considerably modify soil microbial activity and relative C and N availability, both of which are known to regulate soil nitrous oxide (N2O) and nitric oxide (NO) emissions. Minimizing these emissions per unit of crop yield is a prerequisite to minimize the environmental footprint of agricultural production and thus, a policy objective. In our study, we quantified N2O and NO emissions and determined fertilizer-N use efficiencies (NUE) and crop yields of two double-cropping (summer maize/Welsh onion-winter wheat) systems with and without straw incorporation in the North China Plain. Relative to the fertilized treatment without straw amendments, straw incorporation showed a significant inhibitory effect on annual N2O emissions from the maize-wheat system (-31%), but no significant effect was observed for the Welsh onion-wheat system. However, straw return significantly reduced annual NO emissions by >30% for both systems. Meanwhile, straw return in both systems significantly increased the NUE and crop yields by 34-47% and 7-16%, respectively, as compared to the treatment without straw additions. Across the double-cropping systems, annual direct emission factors of N2O, NO and N2O+NO were 0.37-0.57%, 0.08-0.78% and 0.57-1.36%, respectively. Furthermore, a negative relationship between direct emission factors of N2O+NO and crop NUE was observed, highlighting the importance of optimizing NUE for reducing environmental risks of a cropping system. When expressing emissions on a yield basis, straw return significantly reduced annual yield-scaled N2O+NO emissions by 15-42% for both systems. Overall, our results show that the combined application of crop straw and synthetic N fertilizer is a promising N management strategy for maximizing crop yields while mitigating N-trace gas emissions.