Biogas slurry substitution reduced nitrous oxide emissions without compromising crop yield in a winter wheat-summer maize rotation system
Biogas slurry (BS) produced by anaerobic treatment of manure and organic wastes could be recycled to cropland to sustain crop growth as an alternative source of fertilizers. However, due to a lack of relevant field studies, a detailed understanding of how BS affects crop yield and N2O emissions remains poorly understood. In this study, we conducted a field experiment including the control whit no N input (the control, CK) and different BS substitution ratios (zero% substitution, CF; 50% substitution, 50%BS; 100% substitution, 100%BS) substituted to N with a total of 210 kg N ha-1 rate in winter wheat-summer maize rotation system in the North China Plain. To investigate the effect of BS substitution on the amount and source of N2O emission, we monitored N2O fluxes and analyzed isotopomer ratios of soil-emitted N2O. Furthermore, we investigated changes of the nitrifier and denitrifier communities under BS addition. Results showed that compared with CF, 50%BS and 100%BS significantly decreased N2O emissions by 40.1% and 35.5%, respectively, during the wheat season, and by 31.9% and 49.2%, respectively, during the maize season, while achieving as similar crop yield as CF. Soil NO3--N, temperature and moisture were crucial soil properties affecting N2O emission. N2O isotopomer analysis revealed that nitrification and fungal denitrification accounted for up to 45% of the N2O emission peaks observed after fertilization events in CF treatment. Further SP analysis revealed that BS partially substituted for chemical fertilizer did not alter the contribution of N2O emission pathway. BS substituted for CF decreased the AOB-amoA, nirK, nirS copies by 65%, 41% and 35%. The lower AOB-amoA and nirS may be the key factors for lower N2O emissions in 50%BS treatment. Our results showed that BS partially substituted for chemical fertilizers will be a reasonable practice to maintain crop yields while simultaneously mitigate N2O emission in the North China Plain.