Accumulation of organic carbon was limited to the surface of a duplex soil in the mixed farming zone of south-eastern Australia

Context The goal of increasing sequestration of carbon (C) in soil assumes that management factors can be as influential as intrinsic factors such as climate and parent material. Aim The hypotheses tested in this study were (i) that soil C would increase more in limed than in unlimed pasture treatments, and (ii) that well-managed perennial pasture treatments would accumulate soil C to a greater depth than annual pasture treatments. Method An 18-year field experiment was conducted on a duplex soil in the mixed farming zone of south-eastern Australia. The experiment contained four treatment contrasts: limed and unlimed perennial and annual pasture systems. Soils samples to 120 cm were taken annually and analysed for C and nitrogen (N) concentrations. Soil C and N stocks were calculated. Key results The four treatments produced a similar annual rate of increase in soil C concentration and C stocks. The increase in C stock was confined to the surface 30 cm of soil in all four treatments, leading to the rejection of both hypotheses. Nitrogen concentration and N stocks to 30 cm depth increased significantly over the 18 years, with no difference among treatments. Conclusion Pasture land use increased soil C storage by ~700 kg ha−1 year−1; however, the increase was confined to the surface soil. Implication The soil C sequestered in this duplex soil is vulnerable to erosion. The co-retained N might have more value from both production and environmental perspectives.