Application Crop Season Impacts Biochar's Effects on Gaseous Nitrogen Pollutants During the Wheat Growth Cycle

Abstract

Biochar (BC) application to agricultural soil can impact the nitrogen (N) gases losses to atmospheric environment, i.e., the ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission. Under typical rice-wheat rotation, applied at which growth cycle may change the aforementioned effects of BC. We here conducted a soil column experiment to evaluate the responses of N use efficiency (NUE), NH₃ volatilization and nitrous N₂O emission during the wheat season to biochar applied in rice (R) or wheat (W) growth cycle, meanwhile regarding the inorganic fertilizer N input rate, i.e., 72, 90, and 108 kg ha^–1 (named N72, N90, and N108, respectively). The results showed that BC application influenced the wheat growth and final grain yield, particularly increased the grain yield when applied in rice season at N90 to that at N108. Overall, BC addition enhanced the NUE by 11.0%‒53.8% and 32.6%‒52.8% over N90 and N108, respectively. More inorganic fertilizer N input led to higher NH₃ volatilization, also for the emission factor. Interestingly, 19.7%‒34.0% lower NH₃ vitalizations were recorded under treatments with BC applied in rice season, compared with the treatments with fertilizer N only. BC applied at rice season exerted higher effectively on mitigating N₂O emission than that applied at wheat season under three N input rates, i.e., 60.5%‒77.6% vs 29.8%‒34.8%. Overall, considering the crop yield and global warming potential resulting from NH₃ volatilization and N₂O emission of wheat season, N90+BC(R) is recommended. In conclusion, farmers should consider the application time and reduce inorganic fertilizer N rate when using BC.

Keywords: Biochar, crop production, GWP, NH3 volatilization, N2O emission