| Summary: | Urea (U) is the most important nitrogen (N) fertilizer in agriculture worldwide, and as N fertilizer can result in large gaseous losses of NH<sub>3</sub> and N<sub>2</sub>O. Thus, urease inhibitors (UIs) and nitrification inhibitors (NIs) have been coupled with U fertilizers to mitigate NH<sub>3</sub> and N<sub>2</sub>O emissions. However, it is still unclear whether adding NIs and/or UIs to U stimulates other pollutants, while reducing one pollutant. Furthermore, part of the NH<sub>3</sub> deposition to earth is converted to N<sub>2</sub>O, leading to indirect N<sub>2</sub>O emission. To estimate direct and indirect effect of UIs and NIs on the N<sub>2</sub>O-N and NH<sub>3</sub>-N losses from U; therefore, we analyzed multi-year field experiments from the same site during 2004 to 2005 and 2011 to 2013. The field experiments with U fertilization with or without UI (IPAT, N-isopropoxycarbonyl phosphoric acid triamide) and NI (DCD/TZ, Dicyandiamide/1H-1, 2, 4-Triazol) in winter wheat and with calcium ammonium nitrate (CAN) were conducted in southern Germany. Fluxes of NH<sub>3</sub> or N<sub>2</sub>O emissions were determined following each split N fertilization in separate experiments on the same site. Our results showed that U with NIs considerably reduced N<sub>2</sub>O emissions, and adding UIs decreased NH<sub>3</sub> emissions. However, the effect on N<sub>2</sub>O emissions exerted by (U + UIs) or (U + UIs + NIs) was inconsistent. In contrast to the treatment of (U + UIs + NIs), the addition of NIs alone to U stimulated NH<sub>3</sub> emission compared to treatment with U. When 1% indirect N<sub>2</sub>O emission from NH<sub>3</sub> (IPCC emission factor (EF4)) was considered to estimate the indirect N<sub>2</sub>O emission, total N<sub>2</sub>O emissions from (U + NIs) were approximately 29% compared to that from U alone and 36% compared to that from (U + UI), indicating that indirect N<sub>2</sub>O emission from NH<sub>3</sub> induced by NIs may be negligible.
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