A comparative analysis of greenhouse gas emissions from beef cattle grazing irrigated Leucaena leucocephala (Lam.) de Wit cv. Cunningham crops in northern Australia

This study provides a gate-to-gate Life Cycle Assessment (LCA) of the greenhouse gas (GHG) emissions from steers grazing on irrigated Leucaena leucocephala (Lam.) de Wit cv. Cunningham (Leucaena) crops and a surrounding farm property in northern Australia. It involves modeling the GHG emissions from the steers as a project and comparing these emissions with the historic pre-project management and alternative projects on the farm property. The herd consists of 1,250 steers, which are bred on a nearby property and walked to the property analysed in this study. The steers start grazing the Leucaena crops when they are 16 months old and continue until approximately 240 days. At the conclusion of grazing Leucaena, the steers are sold. The results of the project are compared with (i) pre-project historic management, where the steers graze on the bush paddocks until the time of sale, (ii) a proposed project, where the Leucaena crop is extended on previously cleared land and areas currently under forest; and (iii) an alternative project, where Leucaena crops are extended to land that has been previously cleared. The proposed extended and alternative projects include heifers that enter the Leucaena crop at 2 years old and graze for 210 days. The results show significant long-term average reductions in GHG emissions between the current, proposed extended and alternative Leucaena projects and the pre-project historic management (P<0.05), each with reductions of 81%, 41% and 76% of GHG emissions respectively. The long-term average reduction of GHG emissions is significant (P<0.05) per liveweight tonne (LWT) produced for the current, proposed extended and alternative projects, with reductions of 83%, 74% and 95%, respectively. These significant reductions can be attributed to 1) the higher growth rates in the steers, with steers achieving the preferred sale weight in less time; 2) the net primary productivity of Leucaena; and 3) the increased soil carbon content under the crop.