Pushing the Limits of Soil Organic Carbon Storage: The Role of Land Use in Soil Carbon Dynamics

Healthy soils with high carbon content not only enhance agricultural productivity but also serve as significant carbon sinks, by sequestering atmospheric carbon dioxide. Understanding soil organic carbon dynamics is paramount for devising effective climate change mitigation strategies. In our study we analyzed the effect of a continuous dissolved organic matter (DOM) input in a Luvisol under three different land uses: grassland (GR), miscanthus (MI) and bare fallow (BF). We wanted to test if we could observe a maximum carbon content in the smaller fraction (<20μm), comparing our results to our calculations based on regressions for theretical saturation limits taken from the literature. We used a DOM-rich solution and irrigated the samples twice per week for 6 weeks. The GR and MI treatments surpassed the calculated theoretical limit by approx. 20%, contrary to BF which only reached approx. 70% of this theoretical limit. By the end of week 4, even though the carbon input was never interrupted, we observed a limited microbial respiration. It implies that the microbial communities might have focused on POM transformation, contrary to the expectation of them choosing the provided DOM. We also analyzed the change in available specific mineral surface area (SSA) through the experiment and detected a decrease for all the treatments, in line with the results for carbon content. Finally, we calculated the approximated leached carbon for each treatment. Our findings challenge the conventional notion of carbon saturation and underscore the importance of considering soil management practices and environmental conditions, contributing to advancing knowledge in soil carbon dynamics and emphasizing the critical role of adequate soil management in building a sustainable and climate-resilient future.