The role of oxalate-extractable aluminum in regulating soil organic carbon decomposition in agricultural topsoil in humid continental climates: Insights from a long-term incubation field-scale study.

Examining soil carbon losses across various time scales is essential for understanding the potential of soil carbon stabilization. It allows for considering these losses in estimating the net changes in carbon stocks. The soil's intrinsic physical and chemical properties, particularly those associated with the mineral phase, have been suggested to regulate soil organic carbon (SOC) losses. However, the relationship between these properties and SOC losses remains to be determined in long-term experiments. A 600-day incubation experiment was conducted on sieved soil samples (<2 mm) and intact cores (volume=~200 cm3) collected from an arable field in Bjertorp in southwest Sweden with large variations in soil texture and SOC to determine the respiration rate through chamber alkali trap respirometry using a Portable conductivity meter. After the incubation experiment, soil properties (carbon, nitrogen, and pH) were also measured. In addition, previously determined soil texture, oxalate extractable aluminum (Alox), and iron measurements were used to explain the results of the incubation experiment. The ratios between Alox and SOC and Alox and clay content were used as proxies for the protection of SOC. Preliminary results from the sieved soil samples indicate that the respiration rate (µg C-CO2 g-1 SOC h-1) was positively correlated to the Alox:SOC  and clay:SOC ratio. These findings can be interpreted as the absence of SOC protection by Alox and/or clay complexes or interactions. The conclusions drawn from this study suggest the need for additional exploration into the intricate dynamics that influence the fate of soil organic carbon (SOC) associated with mineral phases when assessing carbon stocks.