Managing sheep grazing systems in southern Australia to minimise greenhouse gas emissions: adaptation of an existing simulation model

Abstract

This study summarises the development of a framework in which changes in the management strategies of sheep grazing systems in temperate Australia can be evaluated in terms of their impact on greenhouse gas emissions and financial viability. An exploratory study of a sheep grazing system at Hamilton, in western Victoria, indicates that reducing emissions from some sheep grazing systems in temperate Australia by 20% over the next 15 years will require a similar (i.e. 18%) reduction in stock numbers providing that no other management or technology is used to reduce emissions. This reduction in stock numbers will reduce both farm operating surplus and net cash income by about 15.5 to 17%. The reduction in net cash income represents a direct reduction in the general welfare of the farmer. However, economically viable reductions in emissions may be able to be achieved through changing the time of lambing. Spring lambing resulted in returns per unit emissions which were 15 to 20% greater than those for autumn lambing. Surveys suggest that about two-thirds of all flocks in the area lamb in autumn. Therefore, there exists an opportunity to reduce emissions by the order of 15 to 20% from the region without substantial economic penalties. Overstocking resulted in both increased net methane and nitrous oxide emissions and reduced profitability. The relatively small reductions in stocking rate needed in such situations will reduce greenhouse emissions significantly and also may have the effect of reducing soil and vegetation degradation, thereby improving the sustainability of these enterprises. Implementation of these stocking rate recommendations to reduce greenhouse gas emissions could thus be achieved as part of overall sustainable farming.