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The lack of data is a serious constraint on mallee industry planning, but there is the opportunity to
learn from the sugar industry experience, to increase the amount of revenue generated from the overall
supply chain, and to distribute that revenue appropriately across the supply chain. The most apropriate
supply chain structure and careful management of incentives and rewards will enable the most rapid
systems improvements in the future.
2.8 Discussion
Sugarcane harvesting and transport has many similarities with mallee harvesting. Whole-of-crop
sugarcane harvesting with all material (cane and trash) transported to the sugar mill is the system with
the closest synergies with the mallee harvesting system.
As the mallee industry is still in its infancy, many lessons can be learnt from the mature sugar
industry. It will be important for the mallee industry to consider whole-of-system performance to
ensure components of the supply chain work efficiently as an integrated system. The availability of a
prototype harvester provides an opportunity to evaluate machine performance and assess critical
parameters across the supply chain.
The prototype mallee harvester performs the basic functions of gathering, severing stems at ground
level, feeding all the woody (trunks, stems, branches etc) and leafy biomass (foliage, leaves etc),
through a chipper system and delivering the chipped product into infield transport. There is no
debarking or separation of leafy biomass from woody biomass during the process.
The prototype mallee harvester incorporates a platform vehicle to power and propel the machine and
an attached harvester head arrangement. The harvester head is a single row, over-the-row
arrangement. The prototype mallee harvester is aimed at stems up to 15cm diameter. Alternative
systems (e.g. feller/buncher) will be required as age of tree and size increases.
The current platform vehicle is a Claas Xerion utility tractor. The current prototype mallee harvester
is limited by available power. Hence, future prototypes may not utilise the Claas Xerion as the
platform vehicle. Manoeuvrability and associated soil compaction issues will need to be considered in
the selection of the propulsion system (tracked or wheeled configuration) of the platform vehicle.
The prototype harvester in trials to date has achieved a maximum continuous pour rate of 35 tonne/hr.
The maximum pour rate achieved in trials was 38 tonne/hr for a short period. A continuous machine
pour rate in the order of 60 tonne/hr is required for a viable harvesting system.
Bulk density is a very important performance parameter for an efficient harvesting and transport
system. Bulk density changes with tipping and transport, and the associated impact on product
handling has not been determined. Similarly, the effect of product composition on bulk density is not
known definitively, but experience to date demonstrates that whole mallee biomass and clean pulp
wood chip have similar bulk densities, so the influence of biomass composition appears to be minor.
However the quality of the chipping process – the quality of cut – could potentially have a significant
impact upon material handling properties, and possibly some influence upon bulk density.
There are significant losses from mechanical harvesting of sugarcane, with the majority of losses
occurring in billeting and separation of trash from billets. There is no quantitative data on losses
during mallee harvesting as the prototype harvester has not undergone commercial testing but
preliminary observations are that it should be low. The main loss processes would include gathering,
chipping and spillage during transfer to the infield transport. As there is no separation of the product
on the harvester, there are no losses from this process like in sugarcane harvesting.
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