Reducing enteric methane in northern Australian grazing systems – a synthesis of the role for tropical legumes

Abstract

Enteric methane (CH4) emissions from ruminant livestock are a major source of greenhouse gases in northern Australian grazing systems, where the extensive, low-input nature of production limits the applicability of alternative mitigation strategies such as feed additives. Tropical forage legumes therefore represent one of the few practical abatement options available, offering mitigation through both direct suppression of rumen methanogenesis and indirect improvements in animal productivity. This review synthesises evidence from in vitro, in vivo and farm-scale studies and integrates these findings with production-system modelling and agronomic assessments to evaluate CH4 abatement potential under extensive grazing conditions. In vitro studies demonstrated an average 12.1% reduction in CH4 yield across tropical legume species, while in vivo studies reported a comparable mean reduction of 13.8%. Legume inclusion rate (% of dietary dry matter) emerged as the primary predictor of CH4 response. Production-system modelling across low-, medium- and high-productivity grazing systems showed that legume incorporation reduced emissions intensity by an average of 28%, with approximately 82% of the reduction attributable to productivity gains and 18% to direct suppression of enteric CH4. A multi-criteria prioritisation framework combining CH4 abatement potential with agronomic suitability identified a small number of high-potential species. Leucaena leucocephala consistently produced the greatest direct CH4 suppression, whereas Desmanthus and Stylosanthes spp. offered broader environmental adaptation and greater scalability despite more modest direct abatement. These findings suggest that effective CH4 mitigation in northern Australian grazing systems will require a portfolio of legumes tailored to regional conditions. Tropical legumes are an immediately deployable mitigation strategy, although their full potential will depend on overcoming constraints to establishment, persistence and adoption in commercial grazing systems.