Ammonia emissions from inhibited urea fertilizers – Results on mitigation potential and wheat yield from a multisite experiment across six different regions in Germany

The use of urease- and nitrification inhibitors (UI, NI) is widely accepted in agriculture. However, robust ammonia (NH 3 ) reduction factors for specific compounds and regions are missing. This study of coordinated field trials evaluated NH 3 emissions in Germany across 22 site-year combinations after the application of inhibited urea in winter wheat. Tested fertilizers were urea (U), urea with UI (U+UI), and double-inhibited urea (U+UI+NI). Ammonia emissions were determined using ALPHA samplers, inverse dispersion modeling, and semi-quantitative passive flux samplers. Improving the existing calibrated passive sampling approach, a linear mixed-effects model was developed, accounting for the placement of individual plots within the trial layout. Regardless of the fertilizer treatment, the weather covariates and the clay content significantly influenced the emission factors (EFs, expressed as NH 3 -N per unit N applied). Average EFs for the treatments were 8.0, 3.1, and 3.8% for U, U+UI, and U+UI+UI, respectively. Compared to U, the emission reduction was affected by inhibitor treatment, soil clay content, and temperature, and was highest under high N-loss scenarios. Average reductions were 61% for U+UI and 52% for U+UI+NI. The results suggest a regionalization of EFs and reduction factors. Grain N yield was significantly influenced by inhibitor treatment and was highest for U+UI with 164 kg N ha −1 . U+UI+NI featured the highest absolute yield. With a reduced grain protein concentration, this resulted in a similar grain N yield when compared to U. Combining results of emission and yield measurements, recommendations for specific production targets in winter wheat production are derived. • U+UI (2-NPT) and U+UI+NI (2-NPT + MPA) decrease NH 3 emissions by 61 and 52%. • Environmental covariates influenced emissions and the reduction by inhibitors. • Inhibitors had distinct effects on yield components, however, not always significant. • Improved Transfer Coefficient for calibrated passive sampling. • Coherent field study for new inhibitors and combined yield and emission assessment.