Erosion Impact on Nitrogen Turnover and Retention in Soil (ErosioN)

• Applicants: Dr. Caroline Buchen-Tschiskale; Dr. Maire Holz, Ph.D.
• Subject Area: Soil Sciences
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468948545

Soil erosion has a major influence on the nitrogen (N) distribution and N turnover in soils, yet, there has been little research that holistically studied erosion induced changes in N turnover.In this project, we aim to elucidate the impact of soil erosion on soil-plant mediated N turnover, focusing on changes in the mineralisation-immobilisation-turnover. We hypothesize that mineralization-immobilization-turnover in erosion-affected soils is mainly controlled by (i) soil organic matter (SOM) and N availability, (ii) plant presence and (iii) the presence of free mineral surfaces for development of mineral-associated organic matter (MAOM). Gross mineralization and immobilization will likely be reduced in eroded soils due to reduced SOM and N contents caused by topsoil removal. In contrast, those fluxes will be increased and shifted towards net mineralization in depositional sites with high SOM and N contents due to topsoil accumulation. Eroding soils are expected to exhibit high SOM and N storage capacities due to topsoil removal. They are hypothesized to be characterized by net immobilization because of the large amount of free mineral surfaces. This process is expected to lead to a net increase of soil N stocks in eroded soils.The working program comprises three experiments with different degrees of complexity to study the effect of soil erosion on N turnover. 15N balance approaches and tracing techniques will be complemented by the application of the most recent 15N model (Ntrace) to differentiate gross N transformation processes in soil. In order to gain an initial understanding of soil erosion status on N turnover, an in situ 15N tracing experiment will be conducted in the field (WP1) comparing different slope positions and two sites in northern Germany. In contrast, WP2 and WP3 will focus on improving our process based understanding of short-term changes of different N pools with erosion and will be conducted as microcosm experiments under controlled conditions. In WP2, N turnover will be assessed by 15N tracing using soils representing non-eroded, weakly eroded, and strongly eroded states and considering the effect of crop presence (Barley - Hordeum vulgare L.) on N turnover. WP3 aims to assess the effect of soil erosion on N retention in soil. We will examine how freshly incoming SOM labelled with 14C affects MAOM-N in topsoils and whether this material is allocated to and sequestered in deeper soil layers after being displaced from minerals in the topsoil.Combining isotopic labelling techniques in the field and under controlled conditions will allow us not only to assess the effect of erosion on N mineralization-immobilization-turnover, but also to quantify the influence of soil erosion on N retention in soil. The project will provide quantitative data on simultaneously occurring N turnover processes in erosion-affected soils. These data will allow for adaptation of N management strategies in erosion affected soils.

• DFG Programme: Research Grants