| Summary: | Nitrification inhibitors have been proposed as a tool to mitigate nitrous oxide (N<sub>2</sub>O) emissions from agriculture, which are caused mainly by fertilization. The nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was tested in a winter rapeseed field after dairy slurry application in Central Estonia. N<sub>2</sub>O emissions were monitored using the closed chamber method. Soil and leachate chemical parameters were also analyzed. N<sub>2</sub>O emissions increased from pre-slurry application values of 316 and 264 µg m<sup>−2</sup> h<sup>−1</sup> for the control and treatment plot, respectively, to maximum values of 3130.71 and 4834 µg m<sup>−2</sup> h<sup>−1</sup>, with cumulative emissions during the study period of 12.30 kg ha<sup>−1</sup> for the control plot and 17.70 kg ha<sup>−1</sup> for the treatment plot. The intense precipitation period that began with the application of the slurry resulted in changes in soil moisture and water-filled pore space (WFPS), modifying the nitrification/denitrification balance. Positive significant correlations (<i>p</i> = 0.016 and <i>p</i> = 0.037, for the control and treatment plot, respectively) were found between N<sub>2</sub>O fluxes and WFPS. Future studies should consider the role of nitrifier and denitrifier communities in order to better assess in-field nitrification inhibitor effectiveness.
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