Mitigating denitrification N-losses with optimized liquid organic fertilizer application strategies

Denitrification is the main pathway of nitrogen loss from soils, releasing nitrous oxide (N2O) and dinitrogen (N2). These emissions reduce nitrogen availability for crops and N2O also contributes to climate change. Nitrogen-based fertilizers drive soil nitrogen transformations – including denitrification. The magnitude of resulting emissions varies with management practices, climate and soil properties. Transitioning toward climate-smart agriculture requires understanding the interconnected nature of N-losses and possible trade-offs associated with mitigation strategies. For instance, suppressing N2O emissions through nitrification inhibitors might increase ammonia volatilization (Zhang et al. 2022). Quantifying soil-emitted N2 at the field-scale remains a significant challenge, and consequently, this component is often absent from evaluations of management practices. As a result, agricultural practices that improve nitrogen use efficiency while reducing denitrification losses have yet to be clearly identified.The overall objective of the joint project MinDen is to assess mitigation measures aimed at reducing both direct and indirect denitrification emissions while enhancing nitrogen use efficiency. To this end, a three-year field experiment was conducted across three sites in Germany, representing a gradient from heavy clayey soils with higher emissions to lighter, sandy soil with lower emissions.Four liquid-organic fertilizer application techniques - drag hose with incorporation, slit injection, slit injection with nitrification inhibitor, and drag hose with acidified slurry - were tested alongside two mineral-fertilizer treatments (a standard rate according to crop demand and a 20% reduced rate). At one site, an additional comparison was made between organically- and conventionally-managed fields. Ammonia (NH3), N2O and N2 fluxes were determined using passive samplers, static chambers and the 15N gas flux method. Here, we present the temporal dynamics of NH3, N2O and N2 emissions from the first two years at all three sites. Ultimately, these data sets are being used to validate biogeochemical models to regionalize N-losses from agricultural soils across Germany. Zhang, C., Song, X., Zhang, Y., Wang, D., Rees, R. M., & Ju, X. (2022). Using nitrification inhibitors and deep placement to tackle the trade-offs between NH₃ and N₂O emissions in global croplands. Global Change Biology, 28(14), 4409–4422. https://doi.org/10.1111/gcb.16198