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

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.