THE EFFECT OF TIME OF RATOONING ON SUGARCANE GROWTH IN THE BURDEKIN

THE PURPOSE of this study was to examine the growth of crops ratooned between April and December 1999 in the Burdekin district with the chief interest to determine the productivity of crops started and harvested outside the current harvest season in Australia (mid-June to late November). Relationships between stalk emergence, leaf emergence and thermal time (temperature x time) were similar for all times of ratooning, suggesting that variation in crop growth responses to thermal time are consistent and not affected by the time of ratooning. However, no relationships were found between crop biomass accumulation and thermal time after 32 weeks of age. After 32 weeks of age, time of ratooning and crop age had a significant influence on cane, sugar and biomass yields. Crops ratooned in November and December had significantly lower cane yield than all other times of ratooning. At 52 weeks, the cane yield of crops ratooned in April and May was greater than all other times of ratooning and sugar yield was lowest for crops ratooned in November and December. Dry matter and sucrose content were influenced by the time of the year they were harvested and crop age. Any ratoon crop (regardless of time of ratooning) harvested in April, May or December had significantly lower CCS and dry weight sucrose content compared to those harvested between June and October. Crop age had a large effect on CCS, sucrose and dry matter content, particularly in April, May and December. Under the current cane payment system, gross returns from 52 week old ratoon crops were lowest for crops ratooned in April and December. The conclusion from this study is that the productivity of crops harvested outside the current season is a balance between the effects of time of ratooning on crop growth and the impact of the time of year on sucrose content. Many other factors must be considered to make decisions about when a region should start the harvest season.