Nitrous oxide emissions from manured soils as a function of various nitrification inhibitor rates and soil moisture contents

Application of nitrification inhibitors (NI) coupled with nitrogen additions can reduce nitrous oxide (N2O) emissions. The effectiveness of NIs can be impacted by environmental and soil conditions; however, more information is needed about their optimum application rates, in particular when applied with manure. This study investigated the effectiveness of a range of NIs application rates on reducing N2O emissions from soils receiving liquid manure additions under three moisture contents. Two incubations (A and B) were conducted in Gray Luvisolic (GL) and Black Chernozemic (BC) soils using two NIs [2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) and the new 3,4-dimethylpyrazole succinic acid (DMPSA)]. Soil NH4+ and NO3- concentrations were measured. Beneficial N2O emission reductions caused by NIs were evident at the intermediate and high soil water contents. The averaged emission reductions were 60% and 56% at the 60% and 80% water-filled pore space (WFPS) of the GL soil, respectively. Likewise, a coherent reduction of 58% was also found at the 60% WFPS of the BC soil. Conversely, this emission reduction vanished in this very carbon-rich, clayey BC soil at the highest moisture (80% WFPS). Moreover, as low N2O fluxes occurred with the lowest moisture (40% WFPS), non-significant and minimal emission reductions by NIs were observed, with a null reduction in the BC soil and only 10% averaged reduction in the GL soil at 40% WFPS. Focusing on the N2O emission reduction and nitrification inhibition under a broad range of NIs rates (in incubation B), as soil moisture rose from 60 to 80% WFPS, the most efficient NI rate increased from 0.25 to 1.0 kg a.i. ha(-1) for nitrapyrin and from 0.22 to 0.65 kg a.i. ha(-1) for DMPSA in both soils. In sum, results inform how soil moisture and NI application rates influence the effectiveness of NIs, aiding to improve strategies to reduce N losses from agricultural systems with NI implementation. (C) 2020 Elsevier B.V. All rights reserved.