Effect of topsoil dilution on stabilization of plant derived carbon

Soil tillage often results in tillage erosion in hilly croplands, i.e. to subsoil incorporation into topsoil. However, up to now effect of tillage erosion on the turnover and stabilization of freshly added plant material remains poorly understood. We therefore conducted an incubation experiment comparing topsoil, diluted topsoil and subsoil from an erosion effected field site in north-east Germany. ⁽¹⁴⁾CO₂ respiration was traced over a period of 33 days after addition of ¹⁴C labelled plant residues and ⁽¹⁴⁾C incorporation into several C fractions was studied. The topsoil showed increased C turnover compared to subsoil, however, topsoil dilution resulted in slightly higher C fluxes than in the topsoil, indicative of a more diverse microbial community. The addition of plant residues induced increased decomposition of native soil organic matter, resulting in a priming effect of similar magnitudes in all treatments ranging around 20%. This indicated that C might not be preferentially stabilized in the studied diluted topsoils or in the subsoil. In terms of carbon fractionation, topsoil dilution primarily affected the POM and MAOM (< 20 µm) fractions, with a decline in the order of topsoil > diluted > subsoil. Freshly assimilated carbon was preferentially stabilized in the MAOM fraction (<20µm), especially in subsoils, indicating potential for carbon stabilization in these soils. Overall we observed small effects of topsoil dilution on soil C storage, however, it's important to note that this study used shoot material, which is less intensively retained in soil compared to root material. Topsoil dilution seems to be a promising way to enhance C sequestration but further research is needed to assess its effectiveness for long-term soil carbon sequestration and to evaluate the role of root-derived carbon in these processes.