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A sustainable mallee woody crop industry will require optimised farming and delivery systems. This
may comprise mallee biomass supply on its own, or mallee integrated with other farming systems.
Optimum planting and management arrangements will differ markedly for each scenario. Competition
for soil moisture is important and will depend on local climate and soils. Row layout, tree spacing and
age at harvest will impact harvesting efficiency. Since harvesting and transport will be the major cost
in mallee supply to the processor, designing the layout to maximise harvest efficiency and minimise
cost is of critical import.
Considerable capital has already been expended on establishing more than 13 000 Ha of mallee in
Western Australia. Many of these alley plantings will be too old to harvest economically with a
chipper harvester and alternative systems (e.g. feller-buncher) will be needed to control competition
with existing cereal crops.
It is likely that biomass supply to a processor will comprise block plantings close to the processor,
supplemented by existing feedstock from dispersed alley plantings where appropriate. Block
cultivation may comprise closely spaced alleys (10-30m) on marginal land close to the processor.
Spacing will be site specific and determined by soil moisture competition and yield. Harvest and
transport logistics must be considered in determining layouts. Harvesting efficiency will be improved
when the concentration of biomass per metre of row is maximised and distance between belts is
minimised.
Where mallee planting is not intended for biomass removal, consideration will need to be given to
protocols for carbon credits.
Mallee planting provides vegetative biodiversity in a wheat monoculture and the collateral benefits of
this biodiversity and associated environmental dividend needs to be quantified.
Improvements to the productivity and profitability of the mallee farming systems will require further
R&D to improve biomass yield, tree presentation for cost effective harvesting and better integration
with other farming systems. Farming systems need to be implemented that not only enhance economic
and environmental performance in the farming sector, but also match value chain requirements for
overall efficiency.
Harvesting Systems
Chapter 2 demonstrated that sugarcane harvesting and transport systems have many similarities with
mallee systems. In particular whole-of-crop sugarcane harvesting with all material (cane and trash)
transported to the sugar mill has close synergies with mallee harvesting system.
The sugar industry has shown the importance of considering whole-of-system performance to ensure
components of the supply chain work efficiently as an integrated system. The prototype mallee
harvester provides an opportunity to evaluate machine performance and assess critical parameters
across the supply chain.
The current harvester performs the basic functions of gathering, severing stems at ground level,
feeding all the woody and leafy biomass 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 current system is limited by available power which impacts pour rate, a
critical factor in the delivered biomass cost and future prototypes will need to address this.
Manoeuvrability, mobility and associated soil compaction issues will need to be considered in the
selection of the tracked or wheeled configuration harvester.
The prototype harvester, in trials to date, has achieved a pour rate of up to 38t/hr for a short period. A
continuous machine pour rate greater than 50 t/hr will be required for a viable harvesting system.
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