Drivers of soil organic carbon storage and vertical distribution in Eastern Australia

Aims: Drivers of soil organic carbon (SOC) storage are likely to vary in importance in different regions and at different depths due to local factors influencing SOC dynamics. This paper explores the factors influencing SOC to a depth of 30 cm in eastern Australia. Methods: We used a machine learning approach to identify the key drivers of SOC storage and vertical distribution at 1401 sites from New South Wales, Australia. We then assessed the influence of the identified factors using traditional statistical approaches. Results: Precipitation was important to and positively associated with SOC content, whereas temperature was important to and negatively associated with SOC vertical distribution. The importance of geology to SOC content increased with increasing soil depth. Land-use was important to both SOC content and its vertical distribution. Conclusion: We attribute these results to the influence of precipitation on primary production controlling SOC content, and the stronger influence of temperature on microbial activity affecting SOC degradation and vertical distribution. Geology affects SOC retention below the surface. Land-use controls SOC via production, removal and vertical mixing. The factors driving SOC storage are not identical to those driving SOC vertical distribution. Changes to these drivers will have differential effects on SOC storage and depth distribution.