Tracing nitrogen transformations during spring development of winter wheat induced by ¹⁵N labeled cattle slurry applied with different techniques

Slurry application is often associated with considerable nitrogen (N) losses: ammonia (NH₃), nitrous oxide (N₂O) and a mostly unknown contribution of dinitrogen (N₂) emission, as well as N leaching. Thus, an outdoor lysimeter experiment with growing winter wheat in undisturbed soil cores was set up to follow the transformation of cattle slurry ¹⁵NH₄⁺ and soil ¹⁵NO₃⁻ using a double labeling approach. Slurry treatments included the following application techniques: a trailing hose with/without acidification, and open slot injection with/without nitrification inhibitor. The fertilizer application rate was 67 kg N ha⁻¹. In addition to NH₃ emissions, N₂O and N₂ emissions were measured, as well as N contents and ¹⁵N enrichment of soil N pools and plant compartments. The major gaseous loss pathway was NH₃ with up to 8 kg N ha⁻¹ following trailing hose application, while slot injection significantly reduced NH₃-N losses. Regardless of the application technique, N₂O emissions were low (up to 0.1 kg N₂O-N ha⁻¹), while N₂ emissions reached up to 3 kg N ha⁻¹. No effect on N leaching from topsoil was found. ¹⁵N plant uptake was greater in slot injection than trailing hose treatments. An effect of the nitrification inhibitor was visible in the nitrate contents, but not in gaseous N losses or N leaching from topsoil. Impacts of the application techniques on individual soil N pools were small. The ¹⁵N recovery offered a chance to map the short-term effects and was highest in the soil N_t pool (32 % to 48 % of ¹⁵N applied) with a greater contribution of microbial N than mineral N at beginning of stem elongation. Indications for high N immobilization was derived from the applied N balance approach. In the present case, slot injection scored as the best application technology based on the highest NH₃ reduction, while N₂ and N₂O emissions were not enhanced.