Simulated evaluation of grazing management systems for arid chenopod rangelands in Western Australia

Abstract

A simulation model of the pastoral production system for a chenopod pasture type was used to evaluate pasture and animal production responses to a range of alternative management systems, stocking rates and initial pasture condition states. The management systems evaluated included the Merrill four-pasture, three-herd system, deferred rotation, the Annean system (involving winter grazing only), and continuous grazing. These systems were evaluated at five stocking rates and for four levels of initial pasture condition. Simulations were based on historical rainfall data from a station in the Western Australian arid zone for the period 1963–1987. Formal systems of rotational resting appear to have little prospect for application in this environment. Although animal production in winter was high under deferred rotation, overall these systems were inferior to the Annean and continuous grazing systems in terms of both animal production and pasture response (change in density of desirable perennial plants). In most instances the best pasture response resulted from the Annean system which also achieved levels of animal production (in winter) which were generally second only to deferred rotation. However, at low stocking rates, continuous grazing produced similar pasture and animal production responses to the Annean system for range varying from excellent to poor condition. For range in very poor condition, continuous grazing limited the rate of recovery relative to the Annean system. Although the latter is particularly beneficial under these circumstances, its application depends on the ability to distribute animals at low stock density over summer in order to avoid the potentially serious consequences of heavy grazing pressure at this time.