Pasture management and livestock genotype interventions to improve whole farm productivity and reduce greenhouse gas emissions intensities

Livestock greenhouse gas (GHG) emissions form the largest proportion of emissions from agricultural activities. Here we seek intervention strategies for sustainably intensifying the productivity of prime lamb enterprises without increasing net farm emissions. We apply a biophysical model and an emissions calculator to determine the implications of several interventions to a prime lamb farm in Victoria, Australia. We examine the effects of lamb liveweight or age at sale, weaning rate, maiden ewe joining age, genetic feed-use efficiency, supplementary grain feeding according to green pasture availability, soil fertility and botanical composition. For each intervention, stocking rates were optimised to the lesser of a minimum ground cover or a maximum amount of supplementary grain feed.
Total animal production of the baseline farm was 478 kg clean fleece weight plus liveweight (CFW+LWT)/ha.annum and ranged from 166 to 609 kg CFW+LWT/ha.annum for interventions that replaced existing pastures with annual ryegrass or increased soil fertility, respectively. Annual GHG emissions intensity of the baseline farm was 8.7 kg CO₂-e/kg CFW+LWT and varied between 7.7 and 9.2 kg CO₂-e/kg CFW+LWT for interventions that reduced maiden ewe joining age or increased sale liveweight, respectively. Stocking rate primarily governed production, and in many cases production drove emissions, so interventions that increased production did not always reduce emissions intensity. Indeed, replacing existing perennial ryegrass/subterranean clover pastures with perennial legume swards caused large reductions in both production and emissions, and interventions that increased soil fertility caused large increases in production and emissions; as a consequence both strategies had little effect on emissions intensity.
Stacking several beneficial interventions together further increased production and reduced emissions intensity relative to individual interventions alone. Baseline production increased by 61% by increasing soil fertility, improving feed-use efficiency and reducing the joining age of maiden ewes, while baseline emissions intensity was reduced by 17% by stacking together three similar interventions. We suggest that imposing several beneficial strategies on existing sheep farming systems simultaneously is more conducive to sustainable agricultural intensification compared with imposing any single intervention alone. The best strategies for both sustainably increasing production and reducing emissions intensity were those that decoupled the linkage between production and emissions, such as interventions that shifted the balance of the flock away from adults and towards juveniles while holding average annual stocking rates constant.