Application of RothPC-1 to soil carbon profiles in cracking soils under minimal till cultivation

This study examines soil organic carbon (SOC) profiles in two neighbouring field sites (‘Dog’ and ‘Shed’ paddocks) which share a similar land use history but are characterised by different soil types (euchrozem and vertosol). SOC inventories to 30 cm depth at the two sites were similar however enhanced transport of SOC in the cracking vertosol soils of the Shed paddock produced a significantly flatter SOC profile and higher whole profile SOC inventories at this site. No clear relationship was observed between clay content and SOC distribution at either sample site. Modelling of SOC turnover using RothPC-1 yielded a satisfactory fit to the observed SOC profiles however the soil moisture and temperature values calculated within the model were found to be at odds with 5 year field observations reported from the site. When field measured values for the moisture and temperature were substituted into the model the fit to the observed SOC profiles was significantly poorer indicating that the purely convective transport approach used to model SOC movement within RothPC-1 may not be sufficient to model vertical SOC transport in cracking soils. The results highlight the need for a cautious approach when using RothPC-1 in arid, cracking soil environments