Nitrification inhibitors reduce N2O emissions induced by application of biogas digestate to oilseed rape

Abstract

Winter oilseed rape (WOSR) is the major oil crop cultivated in Europe and the most important feedstock for biodiesel. Up to 90% of the greenhouse gas (GHG) emissions from biodiesel production can occur during oilseed rape cultivation. Therefore, mitigation strategies are required and need to focus on direct nitrous oxide (N2O) emission as one of the largest GHG contributors in biodiesel production. Earlier studies show that nitrification inhibitors (NIs) can reduce N2O emissions derived from N-fertilization. Since information on the effect of biogas digestates with or without NIs on N2O emissions from WOSR fields is scarce, the aim of this study was to evaluate their effects on N2O emissions, mineral N dynamics, and oil yield in WOSR production fertilized with digestate. The study was conducted at five sites across Germany over three years resulting in 15 full site-years data sets. Across all sites and years, N2O emission from WOSR fertilized with biogas digestate (180 kg NH4+-N ha−1yr−1) ranged between 0.2 and 3.5 kg N2O–N ha−1 yr−1. Due to the reduction of the nitrate concentrations following digestate application, application of NI significantly reduced annual N2O emission by 36%. Our results demonstrate that NI can be an effective measure for reducing N2O emissions from digestate application, but its effectiveness depends on soil and weather conditions, and ultimately on the site-specific potential for N2O production and release. There was no effect of NI application on grain and oil yield.