Auditing on-farm soil carbon stocks using downscaled national mapping products: Examples from Australia and New Zealand

From soil sampling, clear differences in carbon stocks to 30 cm were observed when comparing the stocks measured at sites from both countries. In New Zealand, soil carbon stocks were estimated to be as high as 101 t/ha for the top 30 cm of soil. For the Australian sites which were all situated in the Hunter Valley region of NSW, the highest measured soil carbon stocks were 25 t/ha for the top 30 cm. The largest soil carbon variance was observed at the New Zealand hill country farm, where the landscape consists of alluvial terraces, complex broken valley sides and a summit plateau mantled with volcanic ash. In Australia, the presence of subsoil pedogenic carbonate (marl) contributed to high variance estimates relative to the other sites.