Effects of application of inhibitors and biochar to fertilizer on gaseous nitrogen emissions from an intensively managed wheat field

Highlights: • Optimal N fertilizer application rate decreased N₂O, NO and NH₃ emissions. • Biochar application increased SOC, total N and pH, and also NH₃ and N₂O emissions. • Addition of urease and nitrification inhibitors decreased N₂O, NO and NH₃ emissions. • Combined application of biochar and inhibitors reduced N₂O, NO and biochar-induced NH₃ emissions. • Wheat yield was increased by biochar; NUE was increased by biochar and inhibitors. The effects of biochar combined with the urease inhibitor, hydroquinone, and nitrification inhibitor, dicyandiamide, on gaseous nitrogen (N₂O, NO and NH₃) emissions and wheat yield were examined in a wheat crop cultivated in a rice-wheat rotation system in the Taihu Lake region of China. Eight treatments comprised N fertilizer at a conventional application rate of 150 kg N ha⁻¹ (CN); N fertilizer at an optimal application rate of 125 kg N ha⁻¹ (ON); ON + wheat-derived biochar at rates of 7.5 (ONB1) and 15 t ha⁻¹ (ONB2); ON + nitrification and urease inhibitors (ONI); ONI + wheat-derived biochar at rates of 7.5 (ONIB1) and 15 t ha⁻¹ (ONIB2); and, a control. The reduced N fertilizer application rate in the ON treatment decreased N₂O, NO, and NH₃ emissions by 45.7%, 17.1%, and 12.3%, respectively, compared with the CN treatment. Biochar application increased soil organic carbon, total N, and pH, and also increased NH₃ and N₂O emissions by 32.4–68.2% and 9.4–35.2%, respectively, compared with the ON treatment. In contrast, addition of urease and nitrification inhibitors decreased N₂O, NO, and NH₃ emissions by 11.3%, 37.9%, and 38.5%, respectively. The combined application of biochar and inhibitors more effectively reduced N₂O and NO emissions by 49.1–49.7% and 51.7–55.2%, respectively, compared with ON and decreased NH₃ emission by 33.4–35.2% compared with the ONB1 and ONB2 treatments. Compared with the ON treatment, biochar amendment, either alone or in combination with inhibitors, increased wheat yield and N use efficiency (NUE), while addition of inhibitors alone increased NUE but not wheat yield. We suggest that an optimal N fertilizer rate and combined application of inhibitors + biochar at a low application rate, instead of biochar application alone, could increase soil fertility and wheat yields, and mitigate gaseous N emissions.