DOES HARVESTING SUGARCANE CROPS MORE FREQUENTLY INCREASE BIOMASS PRODUCTION?

SUGARCANE BIOMASS IS being considered as a possible alternative to non-renewable energy sources. Biomass can potentially be used to produce ethanol, second-generation biofuels and other renewable commodities and is currently used to produce electricity. Crop management is likely to differ as the value of biomass changes. Current management is based on maximising profit through sugar yield. Potentially nitrogen fertilisation rates, drying-off, ripening and harvest timing could all be manipulated if sugar production was not the only priority. In this paper increasing harvest frequency was investigated as a means of increasing sugarcane biomass production. This hypothesis was based on experimental work showing that biomass production slowed during the late stages of crop development and that substantial yield reductions occurred following crop lodging. Three harvest frequency treatments were established in an experiment in the Burdekin region: 1. A control which consisted of a plant crop and ratoons grown and harvested according to normal industry practice in the Burdekin region (Normal); 2. Cane harvested on an 8-month cycle (Accelerated); 3. Cane harvested on an 8-month cycle over the winter period and a 5-month cycle over the summer period (Double-accelerated). Harvest timing was specifically designed to avoid the wet season period (Jan–Mar). Two sugarcane varieties, KQ228A and MQ239A, were tested. While fresh biomass increased with harvesting frequency, the greatest amount of dry biomass was produced in the normal harvest frequency treatment. This was due to the relatively immature material harvested in the increased frequency treatments having high water content. Crops harvested more frequently also had increased green leaf and cabbage and lower millable stalk and dead leaf components relative to the normal harvesting frequency treatment. These outcomes suggest that, with current cultivars, harvest frequency should remain unchanged in a system where both sugar and biomass production are of value.