Synergistic effects of biological nitrification inhibitor, urease inhibitor, and biochar on NH₃ volatilization, N leaching, and nitrogen use efficiency in a calcareous soil-wheat system

Urease inhibitors (UIs), chemical nitrification inhibitors (CNIs), and biochar (BC) are commonly applied nitrogen (N) management strategies in reducing soil N loss and increasing nitrogen use efficiency (NUE) in agriculture. Biological nitrification inhibitors (BNIs) are natural abilities of certain plant roots to suppress soil-nitrifier activity. They have some advantages over chemical nitrification inhibitors (CNIs), but their effects on N loss and NUE are not critically examined yet. In this study, the synergistic effects of BNI of methyl 3-(4-hydroxyphenyl) propionate (MHPP at dosage of 1000 mg kg(-1)), UI of N-(n-butyl), thiophosphoric triamide (NBPT, 2% of applied_urea_N), and BC (w heat straw biochar, 1% (w/w)) on NH3 volatilization, inorganic N leaching, plant N uptake (N_yield), and NUE are explored through a wheat growth pot experiment. MHPP and BC can increase NH3 volatilization, which increased by 18.5% in the BC treatment and 32.9% in the MHPP_BC treatment. Individual application or co-application of MHPP, NBPT, and BC significantly decreased N leaching by 25.4% to 42.6% (P < 0.05). The treatments of MHPP, BC, MHPP_NBPT, and MHPP_BC significantly increased the N_yield in the range of 7.41%-10.3% and the NUE in the range of 9.94%-13.7% compared with the CF treatment (P < 0.05). The partial mechanism of those strategies in regulating N pathways was by causing niche differentiation between ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA), and changing community structure mainly of AOB. NBPT, MHPP, and BC were found mainly in the targeted Nitrosospira cluster 3a.2 and Nitrosospira cluster 3b. In general, the application of MHPP_NBPT is a promising strategy for simultaneously reducing NH3 and increasing NUE.