Soil carbon sequestration under the tropical perennial legume Desmanthus in northern Australian grasslands

Aims Soil organic carbon (SOC) sequestration in pasture systems has the potential to offset greenhouse gas emissions in beef production. However, the productivity and sequestration potential of extensive, unfertilised pastures in northern Australia are often constrained by nitrogen (N) limitations. To address this, tropical legumes such as Desmanthus offer a promising pathway to increasing N inputs, thereby enhancing both pasture productivity and SOC sequestration. Methods This study examines the impact of Desmanthus on SOC stocks using a space-for-time substitution approach with 12 paired sites across northern Australia. The SOC stocks were measured to 100-cm depth using intact core sampling. Key results Desmanthus-improved pastures stored significantly more SOC than control sites, with an estimated increase of 7.5 t C ha−1 (P < 0.001), equating to an sequestration rate of 0.47 t C ha−1 year−1 over an average of 16 years since establishment. A fitted exponential model suggests that most SOC accumulation occurred within the first decade, after which SOC likely approached a steady state. Increased SOC sequestration in Desmanthus pastures was likely driven by enhanced C and N inputs and greater below-ground biomass allocation. Conclusions The SOC gains from good Desmanthus stands can potentially offset a substantial proportion of herd emissions at low stocking densities in the first decade after establishment. Implications Despite the clear potential for Desmanthus to improve pasture productivity and contribute to SOC sequestration, widespread adoption remains limited. Challenges such as variable establishment success, competition with existing pasture species, and high seed costs continue to constrain its uptake.