Impact of land use variation on soil C change in different agricultural soils in NW New South Wales, Australia

Soils are an important reservoir of terrestrial carbon (C) and can be a source or sink of atmospheric C depending upon management practices. There is increasing international interest in quantifying the magnitude and resilience of this sink. Land-use change can affect C storage and turnover in soils by altering the soil environment. This can also have a profound impact on the sustainability of farming systems and C sequestration or C losses from soil. Change in land use typically results in different rates of erosion, aggregate formation, biological activity and drainage, which will have a significant impact on soil organic carbon (SOC) accumulation. Differing land uses have variable impact on SOC pool and fluxes. For example, decline in SOC under cropping or grazing can be attributed to reduced inputs of organic matter, increased decomposability of crop residues, and tillage effects that decrease the amount of physical protection to decomposition. A system of paired plots have been established in three major soil types (basalt, metasediment and granite) across north-western New South Wales, Australia, through state wide soil monitoring program in order to determine the direction and magnitude of soil C changes associated with major land use change i.e. cropping, native pasture, improved pasture and woodland. Ten random samples were collected from a 25 x 25 m plots at four different depths (to 30 cm) from each land-use which were in close proximity having identical soil type, slope, aspect and elevation. Total soil organic carbon in the surface 10 cm decreased in the order of woodland > native pasture > improved pasture > cropping soils for all three soil types. However, the site variation was large and changes in surface total soil carbon was not significantly different between improved pasture and cropped soils.