Effect of biofertilizer and wheat straw biochar application on nitrous oxide emission and ammonia volatilization from paddy soil.

Biofertilizer can improve soil quality, especially the microbiome composition, which potentially affect soil nitrogen (N) cycling. However, little is known about the responses of nitrous oxide (NO) emission and ammonia (NH) volatilization from biochar-amended paddy soil to the biofertilizer application. Therefore, we conducted a soil column experiment using four 240 kg N ha (equivalent to 1.7 g N pot) treatments consisting of biofertilizer (3 t ha, equivalent to 21.2 g pot), biochar (7.5 t ha, equivalent to 63.6 g pot), and a mixture of biofertilizer and biochar at the same rate and a control (CK). The results showed that the NO emissions and NH volatilizations were equivalent to 0.15-0.28% and 18.0-31.5% of rice seasonal N applied to the four treatments, respectively. Two treatments with biofertilizer and biochar individual amendment significantly increased (P < 0.05) the NO emissions to same degree by 30.2%, while co-application of biochar and biofertilizer further increased the NO emission by 74.4% compared to the control. The higher NO emission was likely attributed to the increased gene copies of AOA, nirK, and nirS. Applying biofertilizer significantly increased (P < 0.05) NH volatilization by 24.7% relative to the control, while applying biochar had no influence on NH volatilization. Co-application of biofertilizer and biochar significantly decreased (P < 0.05) NH volatilization by 12.3% compared to the control. Overall, the net global warming potential based on NH and NO in current study increased by 13.0-26.0% in both the individual- and co-application of biofertilizer and biochar. Interestingly, both individual- and co-applications of biofertilizer and biochar increased the rice grain yield by 16.5-38.3%. Therefore, applications of biofertilizer and biochar did not increase the GHGI. Particularly, the co-applying of them significantly lowered (P < 0.05) the GHGI by 15.2%. In conclusion, biofertilizer and biochar should be co-applied to achieve the goals of environment protection and food security.