Effect of application timing of nitrogen fertiliser on sugarcane crop performance and NUE

Sugarcane crop development is typically slow in the first few months after planting or ratooning. This results in a low nitrogen (N) requirement during the early stages of growth. SIX EASY STEPS® guidance for ratoon crops indicates fertilisation can be delayed up to 6 weeks after harvest, except for late-cut cane that should be fertilised straight after harvest. A trial was established to investigate whether there were benefits of either early or delayed N application on N uptake, NUE and crop performance in a supplementary irrigated farming system at Mackay. Treatments included early and delayed application of N as urea and four N application rates (0, 75, 150 and 200 kg N/ha). Early application was approximately 14 days after planting/harvesting and Late application was approximately 70 days after planting/harvesting. Leaf N %, crop N uptake over time, cane and sugar yield, and nitrogen use efficiency were monitored in the plant, first-ratoon and second-ratoon crops. Nitrogen application timing had no statistically significant effects on the measured crop factors, although sugarcane yield tended to favour early application in the ratoon crops. N application rate increased leaf N %, crop N content and cane and sugar yield. In most cases this was associated with N deficiency at 0N and 75N. There were few statistically significant differences between the 150N and 200N rates. NUE declined with N application rate, but should always be considered in association with crop productivity. The average nitrogen fertiliser uptake efficiency for the site was 0.32. Increasing uptake of fertiliser N is key to overcoming water quality issues associated with sugarcane farming in the catchments of the Great Barrier Reef. The outcome of the trial is consistent with guidance not to delay fertiliser application by more than 6 weeks after harvest.