Relationships between 137Cs and soil organic carbon (SOC) in cultivated and never-cultivated soils: An Australian example

The relationship between soil redistribution processes (i.e. soil erosion and deposition), using the caesium-137 (137Cs) method, and the movement, storage and loss of soil organic carbon (SOC) are examined for a small catchment in south-eastern Australia. While recent studies have found strong and statistically significant relationships between 137Cs and SOC within heavily cultivated (i.e. highly disturbed) landscapes, there has been a dearth of studies in uncultivated conditions. The site used in this study is characterized by different land use histories and soil types and therefore offers a unique opportunity to investigate the relationship between 137Cs and SOC for both cultivated and uncultivated conditions. Depth distribution profiles and hillslope transects were sampled for 137Cs and SOC to examine the relationship between the redistribution of soil particles and SOC at the point and hillslope scale. It was noted that the distribution of 137Cs and SOC with depth in the soil profile differs among land use and soil types. The relationship between 137Cs and SOC was also investigated, with results indicating that there was no relationship between 137Cs and SOC for uncultivated hillslopes. In contrast, strong and statistically significant relationships were found for the previously cropped transects. The lack of a relationship within uncultivated hillslope areas in the current study appears to indicate that SOC and 137Cs are not moving along the same physical pathways or by the same mechanisms, rather it is suggested that the spatial distribution of SOC is a result of biological factors (e.g. biological oxidation, mineralization). The results of this study suggest that the use of 137Cs data to predict SOC redistribution patterns in grazing, largely undisturbed landscapes is problematic. Caution is thus required before using 137Cs to predict the spatial distribution of SOC within uncultivated landscapes in this region of Australia, and within similar dry climatic regions.