Changes in the components of cane and sucrose yield in response to drying-off of sugarcane before harvest

In irrigated sugarcane production, water is usually withheld prior to harvest to dry the field and to raise the sucrose content of the cane. Past research has provided conflicting results on the optimum length of drying-off. An analysis was conducted of pooled data from 37 experiments on drying-off in Southern Africa to: (1) determine the range of responses in sucrose yield and cane sucrose concentration that have been attained under various drying-off regimes; (2) quantify the trade-off between the loss in cane yield under drying-off and any possible gain in sucrose yield and cane sucrose fresh weight (FW) concentration; and (3) identify which components of sucrose yield and sucrose concentration are most sensitive to late-season water deficit, as a means of developing functions for crop simulation models. In only 22% and 61% of the drying-off treatments was there a significant increase in sucrose yield or sucrose FW concentration, respectively. For both sucrose yield and sucrose FW concentration, the average increase attained by drying-off was 8% and the maximum increase was about 15%. Increase in sucrose yield occurred when the decrease in stalk dry mass was no greater than about 10%. This relationship could form the basis for determining the trade-off between reduction in stalk mass and sucrose yield under varying drying-off regimes, and developing economic optima for drying-off severity. Increase in sucrose FW concentration occurred due to an increase in soluble solids and dehydration. Small reductions in fresh yield of cane under drying-off (up to 10%) can be attributed equally to dehydration and reduction in stalk dry mass.