Replacing chemical fertilizer with manure reduces NO emissions in winter wheat - summer maize cropping system under limited irrigation.

Nitrous oxide (NO) emissions from agroecosystems are a major contributor to global warming and stratospheric ozone depletion. However, knowledge concerning the hotspots and hot moments of soil NO emissions with manure application and irrigation, as well as the underlying mechanisms remain incomplete. Here, a 3-year field experiment was conducted with the combination of fertilization (no fertilizer, F0; 100% chemical fertilizer N, Fc; 50% chemical N + 50% manure N, Fc + m; and 100% manure N, Fm) and irrigation (with irrigation, W1; and without irrigation, W0; at wheat jointing stage) for winter wheat - summer maize cropping system in the North China Plain. Results showed that irrigation did not affect annual NO emissions of the wheat-maize system. Manure application (Fc + m and Fm) reduced annual NO emissions by 25-51% compared with Fc, which mainly occurred during 2 weeks after fertilization combined with irrigation (or heavy rainfall). In particular, Fc + m reduced the cumulative NO emissions during 2 weeks after winter wheat sowing and summer maize top dressing by 0.28 and 0.11 kg ha, respectively, compared with Fc. Meanwhile, Fm maintained the grain N yield and Fc + m increased grain N yield by 8% compared with Fc under W1. Overall, Fm maintained the annual grain N yield and lower NO emissions compared to Fc under W0, and Fc + m increased the annual grain N yield and maintained NO emissions compared with Fc under W1, respectively. Our results provide scientific support for using manure to minimize NO emissions while maintaining crop N yield under optimal irrigation to support the green transition in agricultural production.