Impact of urease inhibitor and biofertilizer application on N2O emissions derived from fertilizer using 15N-labelled urea

The introduction of nitrogen (N) fertilizers into agricultural soils represents the predominant anthropogenic contributor to the emission of the greenhouse gas N₂O. The impact of N management choices on nitrous oxide (N₂O) fluxes is contingent upon interactions with both soil biotic and abiotic factors. This study, conducted by the Joint FAO/IAEA Centre in the spring of 2022 at the experimental station of the University of Natural Resources and Life Sciences (BOKU) near Vienna, Austria, aims to explore the influence of a urease inhibitor (UI) and biofertilizer (BI) on N₂O emissions arising from fertilizer use in wheat cropping systems. Employing a randomized complete block design with five treatments and four replicates, including a control treatment (T₁), urea-only application (T₂), urea with UI (T₃), urea with BI (T₄), and urea with both UI and BI (T₅). For this study, the application rate was 50 kg N ha^-1 at the tillering stage (GS 31), except for T₁. N-(n-butyl) thiophosphoric triamide (nBTPT) was used as the UI, and Azotobacter chroococcum as the BI. N₂O gas fluxes were measured using the static chamber method eight times between 3 to 84 days post-fertilizer application, and gas samples were analysed via off-axis integrated cavity output spectroscopy (ICOS, Los Gatos). The highest cumulative N₂O and ¹⁵N₂O emissions occurred in the T₃ treatment, where urea was combined with UI. The emission factors for N₂O in T₂, T₃, T₄, and T₅ were 0.63%, 0.85%, 0.52%, and 0.68%, respectively. Results from ¹⁵N₂O emissions and the fraction of N₂O from ¹⁵N-urea confirmed that UI increased N₂O release from the added fertilizer source. The fraction of N₂O from ¹⁵N-urea reached 26% in the Urea+UI (T₃) treatment, decreasing to 12% in the Urea+BI (T₄) treatment.