Assessing Organic Fertilizer Nitrogen Cycling and Translocation into adjacent Aquatic Systems using 15N Tracing at different Scales

Nitrogen (N) fertilization is essential to increase agricultural productivity, but losses of excess N to the environment, especially from organic fertilization, are causing environmental and health issues. Thus, optimized cattle slurry management targeted to increase nitrogen use efficiency (NUE) can be fundamental for limiting fertilizer N losses from agricultural grasslands. This study aims to further investigate the nitrogen interactions between the pedosphere and hydrosphere at two different scales. At a 1 m² plot scale we assess the effect of different slurry application techniques on NUE and N losses. For this, ¹⁵N enriched slurry was applied using traditional broadcast spreading as well as modern injection techniques. Fates of fertilizer N such as plant uptake, immobilization and leaching are being investigated by ¹⁵N tracing and recovery approaches in order to create full fertilizer N balances. Second, a larger-scale ¹⁵N experiment is conducted on a 200 m² strip of a grassland slope to assess spatiotemporal patterns and pathways of N translocation along the slope to the buffer strip and into the adjacent creek. Soil and plant biomass, sediment within the creek and soil water are being sampled with subsequent ¹⁵N analysis. From the two ¹⁵N tracing experiments, we expect an in-depth understanding of how modern slurry application techniques alter N allocation and loss in the grassland plant-soil system, as well as of the translocation of leached N on a landscape scale.