Optimising harvest date in sugar production: a case study for the Mossman mill region in Australia: II. Sensitivity to crop age and crop class distribution

Optimisation of harvest date in sugarcane production has been shown to increase productivity and profitability. This paper assesses the sensitivity of these responses to crop class and age distribution at harvest, using the Mossman mill region as a case study. Analyses were conducted to assess the consequences of different number of ratoons before ploughing out various fixed crop ages at harvest; and the advantages of fallowing before planting compared to ploughout and immediate replant. Productivity and profitability were found to be sensitive to modifications in model input parameters and constraints. The optimal number of ratoons to maximise both sugar yield and net revenue was found to be three. While the optimal cane supply was not very sensitive to constraints on crop age when it was restricted to 12 months plus or minus 2, there was a significant reduction in net revenue (4 to 5%) when restricted to younger and older crops (9 to 13 and 11 to 15 months). Comparisons of fallow verses ploughout replant showed a gain of 16% in net revenue when all crops were immediately planted after ploughout. This suggests that current fallowing practices are not financially beneficial in the case study region of coastal Mossman. The analysis methodology can be applied in other regions to identify better ways of scheduling cane supply.