The effect of grazing management and legumes on soil organic carbon stocks in pastoral systems relevant to the Australian Carbon Credit Unit Scheme: a critical review

Abstract

Soil carbon dynamics and the potential of management to influence its sequestration and storage is receiving global recognition. The Australian federal government’s emissions trading scheme includes a list of eligible activities whereby a landholder can earn Australian Carbon Credit Units through documenting soil carbon stocks over time. A systematic literature review was undertaken to establish the nature and geographical spread of evidence on the impact of grazing management and legume inclusion in pastoral systems (two of the eligible management activities) on soil carbon stocks. A small number of eligible research articles were identified in Australia (n = 14) from the global literature. Published studies were mainly in New South Wales and Queensland (from 2010 to 2020) on a variety of soil types across all climatic zones. In the majority of studies, there was limited ability to determine the effect of the eligible activities on soil carbon stock due to experimental design and one-off sampling. The legume studies (n = 3) that did show accumulation of soil organic carbon (SOC) had sampled SOC stocks before and after treatment imposed, accounted for equivalent soil mass, and were all conducted on a research station. Interpreting the impacts of management was hindered by insufficient documentation of grazing management history that was often confounded by the biophysical drivers of soil carbon dynamics, and reporting SOC stocks for a fixed soil depth (50% of studies). An investment in resampling those sites sampled more than 10 years ago in close proximity to original sampling location could provide greater insight into the expected levels of SOC accumulation.