Bioeconomics of pasture resources development in sheep production systems

Abstract

Within any grazing system managers need to decide on how to best manage the existing mosaic of pasture resources. This involves the adjustment of stocking rates and grazing management, as well as the use of inputs and existing technologies. The main technologies available to grazing managers are fertiliser, and the sowing of introduced species to improve pasture productivity, quality and persistence. These represent a series of tactical and strategic decisions that need to be made under climatic uncertainty about their degree of success in improving the persistence of desirable species, production and profits. The process represents a complex dynamic decision problem. To address this problem a bioeconomic framework was developed that is capable of modelling the dynamic nature of pasture resource composition and production, and its response to climate and utilisation by grazing livestock. The framework integrates the sequential nature of the decision-making problems faced by sheep producers under climatic uncertainty. This is achieved by developing a paddock-level dynamic pasture resource development (DPRD) simulation model and integrating it into a seasonal stochastic dynamic programming (SDP) model. The SDP consists of four seasonal transition probability matrices which are applied sequentially to solve a recursive equation with the objective of maximising the expected net present value of the sheep enterprise in the long run. The SDP identified optimal tactical and strategic decision rules for each season, in terms of stocking rates and pasture re-sowing as functions of the state of the pasture at the start of a season, which is defined in terms of pasture mass and botanical composition. This process was applied for three soil fertility input systems and three sheep production systems, represented as wool, wool/meat and meat production systems. The outcomes from the process identified pasture state triggers for tactical grazing rests and management, as well as for the optimal replacement of a degraded sward. The optimal target levels for botanical composition, pasture mass and stocking rate were also derived.