Nitrification inhibitor's effect on mitigating N2O emissions was weakened by urease inhibitor in calcareous soils

The application of nitrification or urease inhibitors together with nitrogen (N) fertilizer has been proposed to reduce N losses, including nitrous oxide (N2O) emissions, from agricultural soils. We measured N2O fluxes, crop yield and plant N content over 3 years (2012-2015) to evaluate the long-term effects of nitrification and/or urease inhibitors on N2O emissions, crop production and N use efficiency (NUE) in an intensively farmed wheat maize system in northern China. The experiment consisted of the following five treatments: 1) CK, no N fertilizer; 2) U, urea; 3) NI, urea with 3,4-dimethylpyrazole phosphate (DMPP); 4) UI, urea with N-(n-butyl) thiophosphoric triamide (NBPT); and 5) NIUI, urea with combined DMPP and NBPT. Compared with the U treatment, the NI, NIUI and UI treatments mitigated cumulative N2O emissions by 55%, 40% and 21% in the maize season, respectively, and 47%, 40% and 33% in the wheat season, respectively. The annual direct emission factors of N2O for the U, NI, UI and NIUI treatments were 0.4%, 0.1%, 0.3% and 0.2%, respectively. The NIUI, NI and UI treatments increased the annual crop yield (7%, 6% and 4%) and the NUE (15%, 10% and 7%) relative to the U treatment. The NI treatment showed the best effect on mitigating N2O emissions, but its efficacy was reduced when applied together with UI. This indicates that more studies are required focusing on the performances and mechanisms of these two inhibitors in alkaline and low organic carbon soils. (C) 2017 Elsevier Ltd. All rights reserved.