A continental-scale Inventory of Soil Organic Carbon and Stable Carbon Isotopes from Australian Sandy Soils

The Australian CRC for Greenhouse Accounting has completed a robust continental-scale inventory of soil organic carbon (SOC) storage in well-drained sandy soils of the Australian continent. The SOC reservoir is known to vary spatially with primary variables of climate, texture, drainage, and vegetation conditions, all of which have been addressed by this study. Early phases of this project developed a robust soil sampling and carbon analysis program for the determination of SOC and 13-Carbon pools on a continental scale, which is based on a stratified sampling methodology and simplified analytical techniques. With this methodology a wide range of research problems can be addressed at a variety of spatial scales. The current analytical phase of this project has completed work on soils of coarse texture (sandy) in well-drained conditions, and established a robust relationship of two depth-specific SOC pools to mean annual temperature (MAT) and mean annual precipitation (MAP), while also taking into account the local variability with respect to the distribution of trees and grass. Forty three sites in Australia have been sampled across a wide range of climate regimes and analysed for percent carbon and δ13C, among other key soil physical and chemical properties. Subsequent analysis has produced best-fit empirical relationships of the 0-5 cm and 0-30 cm pools of SOC and 13-Carbon isotopic ratios to MAP and MAT, where correlation coefficients are greater than 0.7. Current research of this project is under way to assess the variability of SOC and 13-Carbon with soil textural conditions (particle size distribution), by analysis along soil texture gradients and by analysis of particle size fractions of each site.