Efficacy of three nitrification inhibitors to reduce nitrous oxide emissions from pig slurry and mineral fertilizers applied to spring barley and winter wheat in Denmark

Mineral fertilizers and livestock manure are major sources of nitrous oxide (N2O) emissions from agricultural soil. Meta-analyses consistently show that nitrification inhibitors reduce N2O emissions, and this study was established to evaluate the efficacy of three selected compounds, DMPP, nitrapyrin and Piadin, to reduce N2O emissions from spring-applied mineral fertilizers (NS 26–13 or UAN) and pig slurry. An N source either alone or combined with an inhibitor were established in 2020 and 2021. In 2020 these treatments were applied in late April before seeding of spring barley, and in 2021 the same treatments were applied in early April to winter wheat under conventional tillage (as in 2020) and no-till management, respectively. Nitrous oxide fluxes and soil mineral N dynamics were monitored during spring only. The range of N2O emissions in the spring barley experiment was typical for this site, bt much higher with pig slurry compared with mineral fertilizers. The winter wheat experiment the following year showed generally low N2O emissions. The effects of nitrification inhibitors, across all treatments, varied between 0 and 90% reduction of N2O emissions. The variable emission levels and treatment effects were explained with reference to climate (temperature, rainfall), distribution of fertilizers, and crop growth, and a need for comparative studies to resolve interacting effects was identified. Overall, the results were consistent with nitrification inhibitors being more effective at reducing N2O emissions from crops where mineral N uptake is delayed relative to the time of fertilization, from mineral N fertilizers in wet or compacted soil, and from organic fertilizers at moderate or even dry soil conditions.