The organic carbon stock in biomass and soil profiles sampled from nearby paddocks with different land-use histories was estimated at 7 sites in the upper Liverpool Plains catchment and the Manilla district of north-western New South Wales, Australia. The distribution of soil carbon concentrations over a depth of 2 m was significantly affected by site and land use. Continuous cultivation and cropping over ≥20 years significantly depleted carbon concentrations compared with grassy woodlands in the surface 0.20 m at all sites and to a depth of 0.60 m at 3 sites. Depth of sampling (0–0.20 v. 0–1.0 m) significantly affected the differences between land uses at most sites regarding estimates of the stock of soil carbon. These results show that differences in soil carbon concentrations and stock size do not remain constant with depth between contrasting land uses. However, comparisons between land uses of the total amount of carbon stored were dominated by the number of trees per ha and the size of the trees in grassy woodlands. The implications of these results for carbon accounting are discussed.

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Australia’s “Direct Action” climate change policy relies on purchasing greenhouse gas abatement from projects undertaking approved abatement activities. Management of soil organic carbon (SOC) in agricultural soils is an approved activity, based on the expectation that land use change can deliver significant changes in SOC. However, there are concerns that climate, topography and soil texture will limit changes in SOC stocks. This work analyses data from 1482 sites surveyed across the major agricultural regions of Eastern Australia to determine the relative importance of land use vs. other drivers of SOC. Variation in land use explained only 1.4% of the total variation in SOC, with aridity and soil texture the main regulators of SOC stock under different land uses. Results suggest the greatest potential for increasing SOC stocks in Eastern Australian agricultural regions lies in converting from cropping to pasture on heavy textured soils in the humid regions.

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