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Abstract
Weeds and fungal diseases cause significant losses to grain crops in Australia. In many cases cultural methods of control are effective. However, it is often difficult for farm decision-makers to select the optimum crop rotation, from an economic point of view, given the technical constraints they face. A decision to plant a particular crop will have implications for both current and future profitability because the current decision will alter the constraints faced by the decision-maker in subsequent periods. Dynamic programming is used to solve the rotation problem faced by grain growers in north-western New South Wales in areas where the weed, wild oats (A vena falua or A vena ludoviciana), and the disease, crown rot (Fusarium graminearum Group I), have a significant effect on wheat yields. The solutions to the dynamic programming problem suggest that in many circumstances a stable rotational pattern is appropriate. In the present case the model is solved for a set of conditions which is relevant to only a small part of the wheat-belt of New South Wales. However, the method can be applied to aid decision-making in individual cases where the user may wish to change the underlying agronomic assumptions of the model.