Commercial cane sugar trends in the Tully sugar district

Commercial cane sugar (CCS), as measured by sugar mills, is in decline in t he wet tropics of Australia. One of these mills, Tully Sugar Ltd has measur ed CCS in the factory as required by legislation and also measured whole cl ean stalk CCS through a small mill, which is free of contaminants. 'Factory CCS' measures the CCS of cane entering the mill, after it has been harvest ed. The harvesting and transport process delivers to the mill cane that is contaminated by extraneous matter such as leaf material and soil. Beween 19 88 and 1998, 1516 blocks were sampled for 'small mill CCS'. These data were combined with block productivity information to determine the trends in sm all mill CCS and factory CCS using a linear mixed model analysis as the dat a were unbalanced. Other data, including the date of harvest for factory CC S, date of sampling for small mill CCS, farm of origin and cane variety wer e available and fitted as random effects in the mixed model. Year was fixed to determine time related trends in the 2 measures of CCS. Small mill CCS was higher than factory CCS and remained constant from 1988 to 1998. Predic ted factory CCS declined from 12.76 units in 1988 to 10.91 units in 1998. W e conclude that the CCS levels in whole clean stalks were actually stable, since small mill CCS remained constant over the IO-year period. Possible re asons for the differences in the trends for the 2 CCS measures are discusse d.