A WEB-BASED SYSTEM FOR PLANNING USE OF LIMITED IRRIGATION WATER IN SUGARCANE

SUPPLEMENTARY irrigation is important for sugarcane productivity and viability of cane farming in many regions where rainfall is the main source of water supply to the crop. Growers have to contend with variable and unpredictable rainfall and with variable water allocations. Because of uncertainty about the season’s water allocations, growers are reluctant to use all their assured allocation early for fear of dry periods later in the growth of the crop. In many seasons allocations are not fully utilised. Growers require some way of assessing the risk of using their water early. An optimising technique (‘Watersense’) for determining the best time to irrigate sugarcane with limited irrigation was developed using the APSIM-Sugarcane model. Watersense aims to find an irrigation strategy that minimises overall water stress and provides the highest yield. A replicated experiment was established on the farm of David Lawson near Bundaberg to compare irrigation schedules based on Watersense (‘Plus’ treatment) and the grower’s considerable experience (‘Grower’ treatment). The treatments were compared by noting irrigation times and yield components, determined by sampling, over three ratoons (2nd, 3rd and 4th). Crop water use was measured with an EnviroSCAN system in the last two ratoons. The Grower and Plus irrigation schedules were remarkably similar for the second and third ratoon crops. In the fourth ratoon, the grower used all the water available by April while Watersense saved some water for May. In the third ratoon, biomass was greater in the Grower than the Plus treatment even though the Plus treatment used more water. In the fourth ratoon, sucrose content was higher in the Plus treatment and resulted in a slightly greater sucrose yield in this treatment.The probability of predicting the correct irrigation date is much greater for irrigations in the near rather than in the distant future. While information about irrigations far into the future may be vague, the information can indicate by when the allocations should be used. Watersense should help growers to use their allocations at the best time and should encourage use of all water allocated every year.