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.