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Transport efficiencies may be possible by leaving residue materials such as bark and twigs behind in
the paddock, but if there is a high enough value for residues, for example as a bioenergy feedstock,
then transporting the mixed biomass will be acceptable. In addition, separation on the harvester has a
low chance of success and will result in a more complex machine design and product losses in field. A
better strategy may be too utilise semi-mobile equipment to undertake product separation at nodes
close to the biomass source and then transport different products to different markets.
Sugarcane harvester field efficiencies are typically 30% to 50%, whereas for mallee, modelling
indicates field efficiencies could be 70-80%. This is the consequence of long row lengths and slow
harvesting speed, resulting in a reduced number of times the harvester needs to turn per hour of
operation and per tonne harvested.
The dispersed nature of the mallee crop will have a significant upon field efficiency, with yields per
paddock hectare of less than five tonnes per hectare, and typically around one green tonne per hectare.
Infield haul distances will be relatively long and vary widely over short periods, which will make the
logistics of harvesting and hauling complex. To simplify this part of the process, the introduction of a
shunt truck between the haulouts and the road transport is under consideration, as it should allow the
harvester and its associated haulouts to work closely together and introduce important flexibility into
the farm operations.
Harvest timing is restricted to the winter and spring seasons in Australian sugar cane, whereas mallees
could, with some qualifications, be harvested all year. This changes the scale of operations
significantly, in that a one million tonne per season sugar mill processes at the rate of about two
million tonnes a year. In comparison, a large bioenergy conversion factory might require about
100,000 to 200,000 green tonnes of biomass over a whole year. While mallee road transport logistics
will consequently be relatively simple, the dispersed mallee crop and long infield transport distances
will make on-farm logistics relatively complex and expensive. Extensive use of sugar cane logistics
and harvester monitoring systems will help the new mallee industry.
The mallee industry will also benefit from the comparatively stable nature of the ex-harvester product.
Green biomass can be stored for periods of a few days, and after upgrading and drying the finer
components of the biomass, storage of weeks should be feasible. This is a significant point of
difference with sugar cane which has cut-to-crush intervals of only hours, which makes the logistics of
a mill’s supply chain complex.
Payment systems and business structures vary in sugar cane and provide a range of models from
which a new mallee industry will be able to choose. The new industry has the opportunity to set itself
up so that responsibilities and rewards are properly aligned and the value added along the supply
chain can be appropriately shared amongst the participants – to increase the size of the cake for the
benefit of all.
At equivalent pour rates, the cost of sugarcane harvesting is less than half that of the estimated cost of
mallee harvesting. The actual cost of mallee harvesting is unknown but modelling a hypothetical
system using the Harvest Haul Model (Sandell and Prestwidge 2004) for this project demonstrates the
importance of pour rate and tonnes per harvester per year in reducing per tonne costs. The high power
requirement for mallee chipping and the low speed at which harvesters can travel while cutting trees
will limit the capacity of the new industry to reduce per-tonne costs.
Key considerations regarding sugar and mallee harvesting systems and the impact on the supply chain
are tabulated in Appendix 1 of the document.
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