Effect of nitrification inhibitor (DMPP) on nitrous oxide emissions from agricultural fields: Automated and manual measurements.

Nitrogen fertilisation contributes significantly to the atmospheric increase of nitrous oxide (NO). Application of nitrification inhibitors (NIs) is a promising strategy to mitigate NO emissions and improve N-use efficiency in agricultural systems. This study investigated the effect of NI, 3,4-dimethylpyrazol phosphate (DMPP) on NO mitigation from spring barley and spring oilseed rape. Manual and automatic chamber methodologies were used to capture spatial and temporal variability in NO emissions. In a second experiment, we study the effect of N fertiliser levels without NI (0 %, 50 %, 100 %, 150 % and 200 % of recommended amount of N fertiliser), as well as 100 % of N with NI on NO emissions in spring barley. The automated chamber measurements showed dynamics of NO changes throughout the season, including positive and negative peaks that were unobservable with manual chambers due to low temporal resolution. Although not significant, application of NI tended to reduce NO emissions. The reduction was on average 16 % in spring barley and 58 % in spring oilseed rape in manual chamber measurements. However, NO reduction was 108 % in continuous automatic chamber measurements in spring barley. The NO EFs for the growing season were very low (0.025 % to 0.148 %), with a greater reduction in EF in spring oilseed rape (76 %) than in spring barley (32 %) with NI application. A positive correlation (R = 80 %) was observed between N fertiliser levels and NO emissions. Crop yield and crop N uptake were not significantly affected by the use of NI. This study highlighted that NI can reduce NO emissions, but the reduction effects are plot, crop and microclimate specific. Long-term experiments with continuous plot-scale measurements are needed to capture and optimise NO mitigation effect of NIs across wide variability in soils and microclimates in agroecosystems.