Influence of soil parent material and clay content of Dermosols on soil carbon content in Tasmania

Influence of soil parent material and clay content on soil carbon, in Tasmanian Dermosol soils. A wide variety of Dermosol order soils were sampled and analysed for Total Organic Carbon (TOC) throughout Tasmania as part of the Soil Carbon Research Project (SCaRP). Dermosols are the most common soil order in Tasmania but they vary considerably in colour, clay content and texture. Much of this variability can be attributed to differences in Soil Parent Material (SPM). Alluvial parent materials often result in dark grey sandy loam or loam A horizons. Igneous parent materials often result in brown clay loam A horizons with well developed blocky structured B horizons. Tertiary sediments often result in grey loam A horizons grading to yellow-brown light clays. These three broad parent material classes have distinctly different mineralogy and provide a good case study to examine whether these differences in SPM and associated mineralogy influence TOC. The effect of SPM on TOC within the Dermosol order was analysed by a spatial mixed model following normalisation of explanatory variables such as rainfall and cropping intensity. Clay contents were estimated by texture tests performed on homogenised subsamples. The effect of clay content on TOC was analysed by attributing a quantitative clay content value, so that regression models could be used.