Environmental Engineering Reference
In-Depth Information
2007). R:S ratios of 2.5-year-old EG planted at 100-2000 trees/ha decreased with increasing plant-
ing density (Eastham and Rose 1990). Roots may be unsuitable for bioenergy because of soil con-
tamination. If roots are not utilized and need to be removed, species with high R:S ratios, e.g.,
E. occidentalis , may not be desirable.
The whole tree could be harvested and roots removed (Harper et al. 2000). Alternative harvest-
ing scenarios include separation and retention of leaves to maintain site fertility (Sochacki et al.
2007). In the case of root retention in the ground for pasture rather than cereal cropping, P. radiata
would be preferred as root decay would allow cereal cropping sooner. Methods to harvest tree crops
with roots may be affected by tree size and their respective root systems. Trees grown at 500 trees/
ha may be difficult to harvest with typical harvesters (Mitchell et al. 1999).
With high stocking densities and optimal slope position, 3-year biomass yields of 15-22 tons/ha
were possible, dependent on species. When averaged across the landscape, yields were more modest
and ranged from 12 to 14 tons/ha. These were achieved in lower than normal rainfall conditions;
with normal conditions and higher planting densities, higher yields may be possible. To maximize
biomass production and water use, planting density, water availability, and species must be matched
to site. There are significant opportunities to expand forest bioenergy in Australia through dis-
tributed electricity generation and production of ethanol and bio-oil. Utilizing the large amounts
of readily available forest residues would generate greenhouse benefits, assist forest regeneration,
and improve forest management. New forests in low rainfall environments would also provide resi-
dues for energy production, thus enhancing their overall viability. A recent mandate that electricity
retailers increase renewable energy production by 9.5 TWh annually has created a small, relatively
high value ($10-12/delivered green t) biomass market (Wright 2006).
Producing biochar from farm or forestry waste could have many benefits: generation of renew-
able electricity, liquid and gas biofuels, activated carbon, eucalyptus oil, heat or low-pressure steam,
and a net sequestration of CO 2 (McHenry 2009). With new policies and initiatives, the profitability
of these various products is likely to improve, especially if integrated into existing agricultural
production and energy systems.
Higher rates of soil sequestration and lower uncertainties in carbon asset verification, coupled
with lower risks of storing carbon in soils, make integrating biochar applications and agricultural
SOC into carbon markets appealing. Carbon markets that include agricultural SOC will enable
farmers to trade sequestered biochar soil applications and facilitate expanding new technologies
that improve farm productivity and energy security.
Growing SRWCs on surplus and degraded agricultural land could be environmentally beneficial
(Bartle et al. 2007). Dryland salinity in southern Australia could be ameliorated using SRWCs.
At A$35/green ton and a water use efficiency of 1.8 dry g/kg of water, SRWCs could produce 39
million per year of dry biomass from 1.5% and 8% of farmland in the 300-400 and 400-600 mm
rainfall zones, respectively, of the southern Australian wheatbelt.
The relatively low cost of fossil fuels in Australia generally limits the development of bioenergy
(Baker et al. 1999). The greatest prospects are therefore crops that yield a commercial product (e.g.,
eucalypt oil) or provide environmental benefits (beneficial re-use of wastewaters, salinity control
in catchments) as well as bioenergy. The economics of bioenergy projects are highly site-specific.
The “Integrated Oil Mallee” project in Western Australia involves more than heat and power
generation (Baker et al. 1999; Sims et al. 2006; Bartle et al. 2007). Biomass will come from grow-
ing SRWC eucalyptus mallee to help solve the dryland salinity problem on croplands. The mallees
are Eucalyptus species (e.g., E. horistes , E. kochii , E. angustissma , E. loxopheleba , and E. poly-
bractea ) with a multi-stemmed habit, lignotubers, and high oil concentration in their leaves, usually
90% cineole; elite lines have total oil content of 3.2% of leaf fresh weight. Mallee oil has short-term
fragrance and pharmaceutical markets and a potential long-term market as a solvent degreaser. By
1999, 12 million oil mallee had been planted on approximately 9000 ha. Linear hedges (twin rows)
will be harvested on a 2-year cycle yielding approximately 20 Mg/km FW. Harvesting trees on a
3  to 4 year cycle will provide pharmaceutical oils, activated carbon, heat and power, renewable
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