Long-term efficiency of cropland management strategies for the mitigation of soil organic carbon losses

In the last decades, declining trends of soil organic carbon (SOC) were observed in agricultural soils as a result of unsustainable management and climate change. Improved management of agricultural soils is needed to mitigate SOC losses and an associated decline in soil fertility and functionality. The present study assesses the effect of different agricultural management strategies on SOC content in a long-term field experiment (1983–2021) in Puch/Fürstenfeldbruck, Germany. The management strategies included different organic amendments (straw, slurry, farmyard manure, legume, and non-legume cover crops) in addition to varying levels of mineral nitrogen (N) fertilization. The results showed a generally decreasing trend in the SOC content of the control as well as for most of the management strategies. However, different management strategies exhibited a pronounced temporal differentiation of the SOC content depending on the organic amendment. Specific management practices such as the incorporation of cereal straw and the cultivation of cover crops contributed to the mitigation of SOC losses to some extent. However, only the combined application of organic fertilizers (slurry), incorporation of cereal straw and the integration of a cover crop was able to fully mitigate the SOC loss and maintain the SOC level throughout the observation period. Moreover, the results indicated that substantially increased yields induced by the application of N fertilizer only marginally contributed to SOC loss mitigation, questioning the reliability of yield-based C input estimation. Given the potential SOC decline in arable soils, it is imperative to implement the full range of improved agricultural management practices, such as cultivating cover crops, returning harvest residues, and applying organic fertilizers to secure soil fertility and functionality. • The majority of agricultural management strategies led to a decline in soil organic carbon content from 1994 to 2021. • Climate change and changes in agricultural management practices assumed to be key drivers of soil organic carbon depletion. • Increasing the main crop yield exerts a negligible effect on soil organic carbon loss mitigation. • The study highlights limitations of yield-based C input estimations. • Only combined organic fertilization, straw incorporation and cover crop cultivation can mitigate SOC losses in the long term.