Productivity trends in sugarcane in the wet tropics

Production trends in the wet tropics of Queensland were analysed for the period 1960-1995. There were gains in tonnes cane per hectare (TCH) and losses in CCS in all districts, with tonnes sugar per hectare (TSH) changing little. A detailed study was made for Babinda, Tully and Mulgrave mill areas where TCH rose 11,21 and 23% respectively, CCS fell 15, 12 and 10%, and TSH changed by -7, +6 and + 11 %. Varietal improvement was estimated to have increased TCH by 26, 30 and 12%, and CCS by 7, 3 and 15%, but other factors decreased both except for TCH at Mulgrave. Losses in CCS are substantially explained by increases in extraneous matter and proportion of billets derived from suckers. Varietal gains in TCH were offset by various combinations of shifts from fallow plant to replant cane, extended ratoons, changes from burnt cane to green cane trash blanketing, and harvesting losses of millable stalk. On the other hand, TCH gained from increases in extraneous matter. In addition to long-term trends, there is annual variation in CCS, largely associated with rainfall, there being both transient (reversible) and irreversible effects. The large year-to-year fluctuations in TCH are considered to be strongly associated with weather, in which some consequence of excessive wetness dominates in the higher rainfall mill areas. Low radiation also depresses productivity.