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 Nt 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.