Carbon stocks in Tasmanian soils

Soil carbon (C) stocks were calculated for Tasmanian soil orders to 0.3 m and 1.0 m depth from existing data sets. Tasmanian soils have carbon stocks of 49 – 117 Mg C/ha in the upper 0.3 m with Ferrosols having the greatest soil C stocks. Mean soil C stocks in agricultural soils were significantly lower under intensive cropping than under irrigated pasture. The range in soil C within soil orders indicates that it is critical to determine initial soil carbon stocks at individual sites and farms for carbon accounting and trading purposes, because the initial soil C content will determine if current or changed management practices are likely to result in soil C sequestration or emission. The distribution of carbon within the profile was significantly different between agricultural and forested land in Tasmania with agricultural soils having two-thirds of their soil C in the upper 0.3 m compared to half in forested soils. The difference in this proportion between agricultural and forested land was greatest in Dermosols (0.72 vs. 0.47). The total amount of soil C in a soil to 1.0 m depth may not change with a change in land use but the distribution can and any change in soil C deeper in the profile might affect how soil C can be managed for sequestration. Tasmanian soil C stocks are significantly greater than those in states on mainland Australia which reflects the lower mean annual temperature in Tasmania that results in less oxidation of soil organic matter.