Estimating the risk associated with drying-off strategies for irrigated sugarcane before harvest

The development of recommendations for drying-or management in sugarcane is difficult due to climatic variability and lack of knowledge of the sensiti vity of changes in sucrose content and cane yield to severity of water defi cit. Relative cane biomass targets were developed for drying-or irrigated s ugarcane before harvest based on derived relationships between cane yield, cane dry weight, and sucrose concentration, using pooled data from previous field studies. These targets were then linked to a crop-soil model and lon g-term climate data to determine the economically optimum duration of dryin g-or, and its variability from season to season for 2 locations in Australi a and one location in South Africa, for a range of harvest dates and soil t ypes. The crop-soil model was validated on yields measured in 37 drying-or treatments conducted in South Africa and Australia. The simulation results show that the required drying-or duration can be highly variable, although the level of variability is not necessarily correlated with rainfall per se . There were interactions between soil type and harvest date, but not at ev ery location. The systems approach outlined here can be useful in developing recommendati ons for drying-or where experience is limited, such as in expanding areas o f sugar industries, for districts in which the practice of irrigation is in creasing, or for harvest dates outside the current harvesting season.