Application of enhanced-efficiency nitrogen fertilizers reduces mineral nitrogen usage and emissions of both N2O and NH3 while sustaining yields in a wheat-rice rotation system

The application of nitrification and urease inhibitors with urea can increase the residence time of ammonium (NH4+) in soils and thus reduce nitrogen (N) losses to the environment. We therefore hypothesized that these inhibitors would perform better in enhancing crop yield and lowering nitrous oxide (N2O) and ammonia (NH3) emissions in rice preferring NH4+ than in wheat preferring nitrate (NO3-). Additionally, a biostimulant (BS) when co-applied with urea would improve N uptake and thus reduce N loss as well. Thereby, the objective of this two-year field experiment was to evaluate the effects of urease inhibitor (UI) N-(n-butyl) thiophosphorictriamide (NBPT), the new nitrification inhibitor (NI) 3,4-dimethylpyrazole succinic acid (DMPSA), dual inhibitors (UI + NI) (NBPT DMPSA), and a BS on crop yield and soil N2O and NH3 emissions in a wheat-rice rotation system. Treatments comprised no N fertilizer (Zero-N), urea under conventional practice (CN), and urea at a reduced rate by 20% either alone (RN) or combined with UI, NI, UI + NI, or BS. Averagely, RN treatment decreased N2O and NH3 emissions by 29.9% and 21.7%, respectively, but reduced grain yield and N use efficiency by 13.1% and 16.3%, respectively, compared with the CN treatment, although not always significantly. However, the combined use of RN and UI, NI, UI + NI, or BS resulted in comparable grain yield and N use efficiency but with lesser N2O and NH3 emissions by 56.4% and 36.1%, respectively averaged across treatments compared with CN treatment. We demonstrated that both inhibitors performed better in reducing N2O and NH3 emissions in rice than in wheat. Overall, we propose that the application of NBPT, DMPSA, and BS could be an effective strategy to mitigate gaseous N pollution while sustaining crop yields in the wheat-rice rotation system.