Understanding the impacts of pour rate on sugar losses from the chopper harvester

Understanding the impacts of pour rate on sugar losses
from the chopper harvester

Sugar loss from a mechanical harvester is the most significant of all losses in sugarcane production. The pour rate or material flow through the harvester affects the amount of cane loss and extraneous matter (EM) harvested, as well as impacts on crop production in the next season. Cane loss and EM impact on the quantity and quality of crop delivered to the mills, thus influencing the profits of cane growers, harvesting contractors and millers. The aim of this research was to investigate the effects of harvester set up and operation on sugar loss and how this was influenced by different crop nutrient practices.

Field work and data collection was conducted in the Bundaberg, Childers and Ingham districts of Queensland during the 2014–16 sugarcane growing seasons. The sites were aligned with pre-existing nutrition trials arranged in a randomised factorial design with four replicates of nitrogen application rates (0–225 N kg/ha). In the plots of interest, the physical properties of the sugarcane including crop density, stalk length and diameter and leaf percentage was measured immediately prior to harvest. The sugarcane was cut by the chopper harvester with three working fan speeds (650, 850 and 1,050 r/min) and three ground speeds (4, 5 and 6 km/h). Billet and EM samples were collected to understand the impact on billet size distribution, billet quality and loss potential. Trash samples were also collected and analysed for sugar loss. The summation of the various components allowed the full assessment of machine impacts on sugar loss, sugarcane quantity and the economic impacts on the three sectors of the sugarcane industry.

The results showed that high pour rates (driven in the trials by high N application rates) produced an increased level of EM in the cane billets supplied to the mill and reduced the fan capacity to separate trash from billets. The proportions of damaged and mutilated billets at high pour rates were also elevated due to the difficultly in
separating the components by the extractor fan. Conversely, the percentage of sound billets and sugar loss were increased at the low N application as the lighter billets were ejected more easily by the cleaning system than the heavier ones. When the pour rate increased (high ground speed and the fan speed (6 km/h, 1,050 r/min, the commercial cutting setting)), the cane loss and EM were high but the billet supply bulk density decreased. Conversely, operating with the low ground and fan speeds (4 km/h, 650 r/min), the cane loss and the bulk density in the billet supply were reduced but the EM was increased, resulting in low CCS and high transportation cost that reduced the grower’s income. The cutting ground speeds at 4 km/h with 850 r/min of fan speed provided the optimised cutting conditions which were a combination of increased sugar recovery without excessive transport cost. In this situation, the growers’ revenue was increased around 9,700 AU$ per 1,000 t of harvested cane through better CCS and cane supply yield. Under this costing model, the harvesting contractor still achieved a balanced income even with the increased costs during harvesting and transportation. Additionally, the miller received increased returns due to the improved processing performance of the sugar recovery due to the quality of the billet supply (high CCS).

Crop parameters change very markedly between and within fields. This research has shown how these changing parameters can dramatically influence the ability of the chopper harvester to efficiently convert grower efforts on farm, to millable sugar at the refinery. The complex relationship between pour rate, ground and fan speed impacts on the profitability of the three sectors in the sugar industry – grower, contractor and miller. Continuously fine-tuning the harvester settings is important to fully optimise the system compared to the current practise of infrequent adjustment.