POTASSIUM: A CRITICAL ROLE IN SUGARCANE PRODUCTION, PARTICULARLY IN DROUGHT CONDITIONS

POTASSIUM (K) is an essential nutrient for sugarcane production and fulfils a number of important roles in plant growth. Its role in regulating the uptake of water and leaf stomatal opening in plants is of particular interest in view of the periodic drought conditions that affect the Australian sugar industry. However, there are perceptions that the application of K is not always warranted because of large soil reserves, or inputs of K in irrigation water. There are also concerns that the addition of K will affect juice quality and the recovery of raw and refined sugar. The paper summarises the current knowledge and perceptions of K in sugar-cane production and presents the findings of recent investigations. It emphasises the disparity between the amount of K applied as fertiliser and that removed by the crop. It reviews the recent modifications to the K recommendations for the Australian sugar industry, which are aimed at ensuring that soil reserves are maintained without affecting cane juice quality. Data from field trials, pot experiments and leaf analysis trends are presented which indicate that the role of K is more complex than previously recognised and that the ability of soil to supply K, and the plant uptake characteristics, need to be taken into account. The data suggest that varietal differences are important in relation to K uptake and that the current third leaf K critical value may not be appropriate for the more modern Australian sugarcane varieties. They also suggest that luxury consumption of K by sugarcane may be more of an issue with some varieties than others. Potassium is clearly an important nutrient in sugarcane production. Fertiliser use needs to be optimised to ensure the efficient supply, uptake and utilisation of K by sugarcane crops. This will enable sugarcane crops to take up a balanced suite of nutrients and be better able to withstand the drought conditions that periodically occur in the sugarcane growing regions.