HAS THE INDUSTRY BENEFITED BY REDUCING BILLET LENGTH?

OVER THE 40 YEARS since the adoption of chopper harvesting in Australia, there has been a trend in reducing billet length, with an acceleration in this trend in the past decade. Early chopper systems in harvesters generally had two blades/drum, whereas five blade and six blade per drum systems are now common. This change has been driven by the assumptions that shortening billet length will both enhance the cleaning performance of the harvester extractor system, and improve load density. Both these factors are of critical importance at the high harvester operating speeds now deemed essential and the subsequent higher leafy trash levels now common in the industry. While reducing billet length intuitively indicates an increase in load density the change in the length/diameter relationship, or slenderness ratio, is the most important parameter in determining the actual impact of changing billet length. Both the billet length to achieve maximum load density for a crop and the maximum achievable load density in clean billets from that crop are stalk diameter dependent. Increasing leafy EM concentrations change absolute values, but not the relativity associated with billet length and diameter. The association between billet length and trash extraction performance of the harvester is equally complex; however, reducing billet length and/or billet diameter reduces billet terminal velocity, driving an increase in cane loss at given harvester extractor settings. Direct mass loss during the billeting process and the indirect impacts of increased billet damage and product deterioration rates are strongly related to billet length. The paper reports on past research from both Australian and overseas and, in conjunction with the results from field trials conducted in 2016, demonstrates that the net cost to the Australian industry of the move to shorter billets can approach 10% of total industry value and that this is a totally avoidable loss.