Evaluation of the effectiveness of N process inhibitors in paddy rice via a 15N tracing approach

Abstract

Nitrogen (N) stabilizers, e.g. nitrification inhibitor (NIs), urease inhibitor (UIs), or combined NIs and UIs (NUIs) have been recommended to reduce N losses, and improve fertilizer N use efficiency (NUE) and crop yield. However, the effectiveness of N stabilizers on rice yield and NUE varies greatly and the underlying mechanisms are not well understood. We performed a series of 15N tracing experiments in the laboratory and in the field of two paddy soils with contrasting pH (pH 5.18 and 7.83) to evaluate the effects of N stabilizers on gross rates of soil N transformations, rice yield, NUE and N loss. Results showed that in acidic soil the NI and NUI did not significantly affect the NH4+ residence time and the potential risk of N loss (gross nitrification rate (ONH4) + NH3 volatilization (VNH3), ONH4 + VNH3). However, the NI significantly inhibited ONH4 reducing the combined ammoniacal N loss (ONH4 and VNH3) by 19.7% and prolonging the NH4+ residence time in alkaline soil. Similarly, NUI also reduced ONH4 + VNH3 by 15.8%, thus, increasing the residence time of ammoniacal N in alkaline soil. The results of the field trial showed that application of NI and NUI can improve rice yield and NUE by extending a residence time of NH4+ in alkaline soil, but not in acidic soil. This study provided information under which conditions NIs and/or NUIs can be recommended to enhance rice production while reducing environmental impacts.