Optimising harvest date in sugar production: A case study for the Mossman mill region in Australia: I. Development of operations research model and solution

Cane and sugar yields within a sugar mill region can vary with geographical location, harvest date, harvest age, variety and crop class. It is not possible, due to limited mill capacity, to harvest all cane when maximum yields are attained. Given a prolonged harvest season, an important question is how the harvest of individual paddocks of cane should be scheduled so as to maximise net revenue for the entire mill region. This paper presents the application of an optimisation model to the Mossman mill region with the objectives of maximising sugar yield and net revenue in relation to harvest date and crop age. Six years of block productivity data classified according to district, crop class, variety, harvest date, harvest age, cane yield and sugar yield, were used to generate the input parameters for the model. Other inputs were sugar price, growing and milling costs, and transport and crushing capacity. With current crushing capacity and harvest season lengths, an application of the model to maximise sugar yield showed a 4% increase in sugar yield compared to current practice, but a 23% decrease in net revenue due to a shorter crop cycle with less ratoons before replanting. Optimising with respect to net revenue, gave a 3% gain in sugar yield with an 8% gain in net revenue. When crushing capacity was allowed to increase for current season lengths, the model showed a 14% gain in net revenue given fixed milling costs. It is concluded that there is scope for optimising harvest date to improve profitability in this mill region given current harvest season lengths and land area.