Energy Fuels 2010, 24, 2–9 : DOI:10.1021/ef9006438 Published on Web 09/30/2009
Toward Sustainable Production of Second Generation Bioenergy Feedstocks† John R. Bartle* and Amir Abadi Department of Environment and Conservation Perth Australia, Locked Bag 104, Bentley Delivery Centre, Western Australia 6983 Received June 24, 2009. Revised Manuscript Received September 2, 2009
Some analysts point to continuing advances in agricultural technology and declining global population growth rates to predict a substantial surplus of agricultural land by 2050. Such surplus land could be diverted into growing biomass for renewable energy to help overcome the global challenge of climate change. Others suggest that diversion of agricultural land into bioenergy will exacerbate risk of chronic food shortage by 2050. On balance it appears that declining population growth rate, continuing technology advance, and intensifying use of existing global agricultural land could support sufficient food production as well as some bioenergy production. Competitive bioenergy requires development of second-generation (lignocellulosic) feedstocks rather than first-generation (starch, sugar, and oilseed) feedstocks. Secondgeneration feedstocks from woody crops have the potential to complement intensive agriculture and ameliorate its environmental impacts. Woody biomass crops may therefore have a lower effective cost than generally perceived. The potential for woody crops is indicated with an economic analysis of mallee, a woody crop being developed for low-cost biomass production in Western Australia. Mallees are short, multistemmed eucalypts grown in dispersed narrow belts, harvested on a regular short cycle, and regenerated by coppice. When integrated into the dryland agriculture of this region it has the potential to improve the economic and environmental performance of the entire system. and the risk that the world may be heading into a period of chronic food shortage.5-7 This debate stimulated interest in second-generation (lignocellulosic) feedstocks for bioenergy.8 This paper provides an overview of how production of second-generation feedstocks from woody crops might be accommodated into global agriculture without compromising food supply. It focuses on the potential for woody crops to be developed as dual purpose components of agricultural systems, to produce feedstocks for bioenergy and deliver environmental services. It then presents a case study from the southwest of Western Australia where mallee eucalypts are being developed for integration into a dryland winter-rainfall agricultural system with a range of environmental problems.
Introduction The International Energy Agency (IEA) identified two key global energy challenges in their 2008 World Energy Outlook.1 The first is securing the supply of reliable and affordable energy, and the second is effecting a rapid transformation to a low-carbon, efficient, and environmentally benign system of energy supply. They saw this as being “nothing short of an energy revolution” (Executive Summary, p 37). It might be expected that a revolution in the global energy economy would also be a revolution for global agriculture. Energy is not only a major input cost to agriculture, it can also be an output in the form of bioenergy feedstocks. Medium- to long-term projections indicate global oil prices will remain above $US70/barrel (2007 real prices).1-3 In this range agricultural input costs become highly sensitive to petroleum-based input costs, and it becomes attractive to divert first-generation feedstocks such as maize and sugar into ethanol production.4 At the height of the economic boom in 2006-08, the escalating diversion of maize to ethanol production in the US raised strong debate about a “food or fuel” conflict in agricultural land use
The Potential of Agriculture Global agriculture has an impressive record of increased production over the past 50 years. In the 40 years prior to 2000 it fed a world that doubled in population (from 3 to 6 billion), it increased per capita food production by 20%, generated technology advances such that the increase in production has required only an additional 11% of new land, and it reduced the real cost of food by two-thirds.9-12 Aggregate
† Presented at the 2009 Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies. *To whom correspondence should be addressed. E-mail: john.
[email protected]. (1) IEA, World Energy Outlook 2008; OECD/IEA: Paris, 2008; p 569. (2) ABARE, Australian Commodities; Australian Bureau Agricultural and Resource Economics: Canberra, 2009; Vol. 16(1), p 256. (3) The World Bank. Global Economic Prospects ; Commodities at the Crossroads; World Bank: Washington DC, 2009; p 180. (4) Cassman, K. G.; Liska, A. J. Biofuels, Bioproducts and Biorefining 2007, 1, 18. (5) Nellemann, C.; MacDevette, M.; Manders, T.; Eickhout, B.; Svihus, B.; Prins, A. G.; Kaltenborn, B. P. Eds. The Environmental Food Crisis ; The Environment’s Role in Averting Future Food Crises; United Nations Environment Program: Norway, 2009; p 101. (6) (a) The End of Cheap Food. The Economist Magazine 2007, December 8, 11; (b) Briefing: Cheap No More. The Economist Magazine 2007, December 8, 81-83.
Published 2009 by the American Chemical Society
(7) The State of Food Insecurity in the World; Food and Agriculture Organisation: Rome, 2008; p 56. (8) Tilman, D.; Socolow, R.; Foley, J. A.; Hill, J.; Larson, E.; Lynd, L.; Pacala, S.; Reilly, J.; Searchinger, T.; Somerville, C.; Williams, R. Science 2009, 325, 270. (9) FAO. World Agriculture ; Towards 2015/2030, an FAO Perspective; Food and Agriculture Organisation: Rome, 2003; p 432. (10) UN. World Population Prospects: The 2008 Revision, Highlights, Working Paper No. ESA/P/WP; United Nations, Department of Economic and Social Affairs, Population Division: New York, 2009; p 89. (11) World Agriculture ; Towards 2030/2050, Prospects for Food, Nutrition, Agriculture and Major Commodity Groups, Global Perspectives Study Unit Interim Report; Food and Agriculture Organisation: Rome, 2006; p 71. (12) FAO. The State of Food and Agriculture: Biofuels: Prospects, Risks and Opportunities; Food and Agriculture Organisation: Rome, 2008; p 128.
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pubs.acs.org/EF
Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438
Figure 1. US maize yield trend from 1966 to 2005 annotated with technological innovations that contributed to yield gain. From Cassman and Liska.4
global cereal yield increased from 1.4 to 3.05 tons/ha, and the amount of arable land required to produce a given amount of grain declined 56%.9 For example, the advance of maize yields in the USA, annotated with key technology improvements, is given in Figure 1. In the first decade of the new century, a major commodities boom and steep escalation of the petroleum price raised the question: can agriculture continue to keep pace with population growth? On the demand side, the UN medium variant projection is for population to increase from 6 billion in 2000 to 9.1 billion people by 2050.10 The population growth rate is expected to fall to 1.2% in 2010 to 0.3% in 2050 and reach zero growth (or a population maximum) around 2075. On the supply side, extra production from technology advance alone is expected to exceed the extra demand due to population growth.9,11 Furthermore, there is opportunity to intensify use of the current 5 billion ha of global agricultural and grazing land.12 Several studies use forward projections of historic aggregate supply and demand data to indicate that there is capacity to feed the additional 3 billion people, perhaps without any increase in the real price of food, while still producing some first-generation feedstocks for biofuels.3,9,11-14 However, these studies are forward projections with little analysis of factors influencing the ultimate production potential from existing global agricultural land. The energy revolution is a major new variable in looking into the future. The extent to which agricultural production potential may be drawn into supply of bioenergy feedstocks is not clear. To a significant extent, this is expected to be moderated by the emergence of more energy efficient “second-generation” biofuel technologies.1 First-generation biofuels can be produced from food crops containing starch/sugar/oil, where the conversion technologies and markets are well established, and where it has been possible to quickly take advantage of the commercial opportunity provided by the increase in petroleum prices.15,16
Particularly, where these technologies are applied to annual temperate-climate food crops (cereals, sugar beet, oil seeds), the overall process has relatively low energy output compared to energy inputs.17,18 A major attraction of second-generation feedstocks is their abundance, low cost, and ratio of energy output to input. They are lignocellulosic materials that make up the fibrous and woody structural components of plants. These materials are available as primary (in the field) or secondary (processing) residues from agriculture and forestry; as well as tertiary waste (from urban/industrial activity). Primary sources also include herbaceous (grasses) and woody species grown as crops. The herbaceous and woody species being targeted for development as lignocellulosic crops are robust perennial species that can resprout from rootstocks after harvest. In the case of woody crops, this resprouting process is called coppicing. Woody crops in particular have the potential to provide ecosystem services and therefore to complement rather than compete with conventional agriculture. There is considerable current investment in developing second-generation conversion technologies and biomass sources.1,19 Progress in understanding the technical production potential of the global agricultural land base of 5 billion ha is indicated by Lysen and van Egmond.20,21 They reviewed the recent literature and identified several studies that examined (17) Wu, H.; Fu, Q.; Giles, R.; Bartle, J. R. Energy Fuels 2008, 22, 190. (18) Farrell, A. E.; Pelvin, R. J.; Turner, B. T.; Jones, A. D.; O’Hare, M.; Kammen, D. M. Science 2006, 311, 505. (19) Dickmann, D. I. Biomass Bioenergy 2006, 30, 696. (20) Dornburg, V.; Faaij, A.; Verweij, P.; Banse, M.; Diepen, K. v.; Keulen, H. v.; Langeveld, H.; Meeusen, M.; Ven, G. v. d.; Wester, F.; Born, G. J. v. d.; Oorschot, M. v.; Ros, J.; Smout, F.; Vuuren, D. v.; Vliet, J. v.; Aiking, H.; Londo, M.; Mozaffarian, H.; Smekens, K. Biomass Assessment ; Main Report; Lysen, E.; Egmond, S. v. Eds.; Netherlands Environmental Assessment Agency: Bilthoven, 2008; p 108. Available at http://www.pbl.nl/en/publications/2008/index.html [Accessed May 2009]. (21) Dornburg, V.; Faaij, A.; Verweij, P.; Banse, M.; Diepen, K. v.; Keulen, H. v.; Langeveld, H.; Meeusen, M.; Ven, G. v. d.; Wester, F.; Alkemade, R.; Brink, B. t.; Born, G. J. v. d.; Oorschot, M. v.; Ros, J.; Smout, F.; Vuuren, D. van; Wijngaart, R. v. d.; Aiking, H.; Londo, M.; Mozaffarian, H.; Smekens, K. Biomass Assessment - Supporting Document; Lysen, E.; Egmond, S. v. Eds.; Netherlands Environmental Assessment Agency: Bilthoven 2008; p 202. Available at http://www.pbl.nl/en/publications/2008/index.html [Accessed May 2009].
(13) Tweeten, L.; Thompson, S. R. Farm Policy J. 2009, 6 (1), 17. (14) OECD-FAO. Agricultural Outlook 2008-2017; OECD Publications: Paris, 2008; p 229. (15) Hettinga, W. G.; Junginger, H. M.; Dekker, S. C.; Hoogwijk, M.; McAloon, A. J.; Hicks, K. B. Energy Policy 2009, 37, 190. (16) Van den Wall Bake, J. D.; Junginger, M.; Faaij, A.; Poot, T.; Walter, A. Biomass Bioenergy 2008, 33, 644.
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Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438
Table 1. Technical Annual Biomass Production Potential at 2050 in EJ source residues from agriculture, forestry and wastes surplus forestry production additional to residues primary biomass crops on surplus mainstream agricultural land primary biomass crops on marginal and degraded land progress along the learning curve with these new crops/industries
Table 2. Comparison of IEA Scenarios by % Market Share by Fuel Source at 2030
amount in EJ
coal oil gas nuclear hydro biomass % other total fossil scenario % % % % % % renewables EJ %
100 60-100 120
reference 29 550 ppm 23 CO2-e 450 ppm 17 CO2-e
70 140
30 30
22 22
5 7
2 3
10 12
2 3
713 649
81 75
30
20
9
4
15
5
602
67
of demand and supply. The reference scenario provides a baseline against which to compare alternative scenarios. The reference scenario shows that fossil fuels would continue their dominance of world energy supply maintaining a share of more than 80% of consumption. Oil retains its ranking as the major source, although its 2030 share declines to 30%. With a growth rate about half that of coal, oil would be passed as the major source soon after 2030. Biomass supplied slightly more than 10% of the annual global primary energy demand in 2006, exceeding both hydro and nuclear. Biomass and other renewables would barely increase their share (from 11 to 12%) by 2030. Annual growth rate for all sources is projected to be 1.6% and for biomass 1.4%. As a contrast to the reference scenario, the IEA1 provides two additional policy scenarios that constrain emissions to achieve target levels for long-term stabilization of atmospheric CO2 equivalents (CO2-e) concentration at 450 and 550 ppm. These two scenarios straddle the progressive but plausible range of emissions control targets. The IPCC30 estimates that a 450 ppm CO2-e scenario will limit the increase of average global temperature to 2 °C over preindustrial levels and a 550 ppm CO2-e scenario will limit the increase to 3 °C. In achieving these scenarios cap-and-trade systems are assumed to play an important role in the OECD nations. In these markets, the price of traded carbon is expected to reach US $90/ton CO2-e (in real 2007 dollars) under the 550 ppm CO2-e and US$180/ton under the 450 ppm CO2-e scenario. The reference scenario will also eventually stabilize, but later than the two climate policy scenarios, and at an atmospheric CO2-e concentration of 1000 ppm with a global average temperature increase of up to 6 °C.30 The IEA1 considers that a temperature rise of this order is well beyond what the international community now regards as acceptable. Table 2 shows the global percentage market share of primary energy sources at 2030 under the reference and policy scenarios. Under the reference scenario, the fossil fuel share of total primary energy was 80% in 2006 and remains at this level to 2030. Under the two policy scenarios, primary energy demand to 2030 declines by 9% and 16% (550 and 450 ppm CO2-e respectively) and the fossil fuel shares decline to 75% and 67% respectively. The “other renewables” source has the strongest increase across scenarios but starts from a low base. The other nonfossil fuels all expand strongly, with biomass projected to have a 12 or 15% (550 and 450 ppm CO2-e respectively) share of total global energy demand by 2030. Taking into account the inertia in major restructuring of world energy sources, the IEA1 projections to 2030 are not inconsistent with the scale of bioenergy utilization foreshadowed in the IEA Bioenergy28 assessment to 2050, with much of the increase in bioenergy coming on-stream after 2030.
factors affecting biomass production potential on a global scale.22,23,25-27 They set out to build on these studies, in particular, to deal coherently with impacts and linkages of biomass production with food supply, water use, biodiversity, carbon emission regulations, and economics. They used regional and site specific resolution in dealing with these linkages. They estimate technical resource potential, identify gaps in current knowledge, and provide guidelines for policy on sustainable biomass development. They defined the potential for biomass production from several sources, in addition to meeting demand for food, at 2050, of about 500 EJ/year (1018 Joules/year) as shown in Table 1. Lysen and van Egmond20 also undertook economic analysis to determine the competitiveness of biomass compared to other energy options. For power generation, where there is competition from other renewables (wind, solar, solar-thermal, geothermal), they found that demand would decline for a farm-gate biomass price over the range US$2-3/GJ (or ∼US $24-36/green ton for fresh biomass with an energy content of ∼12GJ/ton in 2008 dollars). When second-generation technologies are developed to produce transport fuels, and where the major competitors are oil and gas, a price of US$4-5/GJ would be competitive. They found that these prices would not be attractive enough to fully utilize the technical biomass supply potential. On the basis of this work IEA Bioenergy28 estimates that bioenergy will supply about 250 EJ (25-33% of global energy supply) by 2050. More detailed assessments of the bioenergy market share out to 2030 are presented by IEA in their World Energy Outlook.1 They use their World Energy model29 to make global projections based on specified assumptions. Their baseline projection, the reference scenario, incorporates national governments’ energy policies that were adopted or enacted up to mid-2008, and with other established energy market trends, extrapolates these according to the underlying forces (22) Wolf, J.; Bindraban, P. S.; Luijten, J. C.; Vleeshouwers, L. M. Agric. Syst. 2003, 76, 841. (23) Hoogwijk, M.; Faaij, A.; de Vries, B.; Turkenburg, W. C. In Hoogwijk, M. On the Global and Regional Potential of Renewable Energy Sources; Ph.D. Thesis, Utrecht University: 2004. (24) Hoogwijk, M.; Faaij, A.; Eickhout, B.; de Vries, B.; Turkenburg, W. C. Biomass Bioenergy 2005, 29 (4), 225. (25) Obersteiner, M.; Alexandrov, G.; Benı´ tez, P. C.; McCallum, I.; Kraxner, F.; Riahi, K.; Rokityanskiy, D.; Yamagate, Y. Mitigat. Adaptat. Strategies Global Change 2006, 11 (5-6), 1003. (26) Rokityanski, D.; Benitez, P.; Kraxner, F.; McCallum, I.; Obersteiner, M.; Rametsteiner, P. C.; Yamagata, Y. Technol. Forecast. Soc. Change 2007, 74 (7), 1057. (27) Smeets, E. M. W.; Faaij, A. P. C.; Lewandowski, I. M.; Turkenburg, W. C. Prog. Energy Combust. Sci. 2007, 33 (1), 56. (28) Bauen, A.; Berndes, G.; Junginger M.; Londo M.; Vuille, F.; Ball, R.; Bole, T.; Chudziak, C.; Faaij, A.; Mozaffarian, H. Bioenergy ; A Sustainable and Relaiable Energy Source: A Review of Status and Prospects; IEA Bioenergy: 2009. Available at www.ieabioenergy.com. (29) IEA. World Energy Model ; Methodology and Assumptions; International Energy Agency: Paris, 2008. http://www.iea.org/weo/docs/ weo2008/WEM_Methodology_08.pdf [Accessed June 2009].
(30) IPCC. Climate Change 2007: Synthesis Report, Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change; Pachauri, RK; Reisinger, A; Eds.; IPCC: Geneva, 2007.
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Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438
Both studies indicate a relatively small role for bioenergy due to the economic factors in biomass supply constraining market penetration to about half the technical potential. Using an area conversion for biomass in EJ of 4.2 Mha/EJ (yield 20 green tons/ha/yr at 12 GJ/ton), the 450 ppm CO2-e scenario production area would need to be 374 Mha or about 7.5% of the global agricultural land area. To put this into context, in terms of land area it is similar to the proportion to set-aside (withdrawn from production) agricultural land area in the EU,3 or in terms of biomass sources, it is not much greater than the supply of biomass residue and surplus forestry production predicted to be available in 2050 (see Table 1). If residue biomass streams take priority in supply, there would be little role for new primary biomass crop production. If primary biomass crops are to take a more prominent role in future energy supply they will have to be available at reduced cost or increased value over what has been assumed in the studies examined here.1,8,20,21 Increased value may come from better biomass quality, potential for additional or higher value coproducts, or provision of complementary benefits within agricultural systems. Woody crop practice can be designed to be complementary to conventional agriculture and do this to an extent that may reduce the effective overall cost of biomass. The potential for such benefits is implicit in the list of gaps in knowledge presented by Lysen and van Egmond20,21 and their proposition that future cost reduction can be expected due to technological learning. The complementary benefits of biomass crops are the theme of the next section.
However, when assessed in the wider context of the economic, social, and environmental performance of agroforestry systems, complementarity is more readily observed. Agriculture can generate negative outcomes both internal (e.g., salinity or erosion on the farm) and external (e.g., nutrient enrichment of runoff into streams, CO2 emissions especially from livestock), and these might often be moderated by adding a woody crop component.36,37 A full accounting of land-use system performance should include direct and indirect costs and benefits.8 There are many examples of major agricultural regions where land use sustainability is in question and where the biophysical benefits of incorporating woody crops might be utilized. The Mississippi basin in the USA is a good example of highly productive temperate agriculture. Continuing intensification of agriculture has generated a major problem with nutrient, sediment, and agrochemical outflow to wetlands, streams, rivers, and ultimately to the Gulf of Mexico. The nitrogen discharge to the Gulf has created a persistent hypoxic zone up to 20 000 km2 in extent.38 It is recognized that the problem cannot be managed by agronomic practice alone. The evidence and resolve to implement specifically designed and managed stream-side buffers or riparian strips along the vast Mississippi drainage network is emerging.39,40 These strips may need to be ∼15 m wide on each side of a stream40 and have components with grasses, shrubs, and trees to best deliver the range of remedial functions. The area withdrawn from conventional agriculture could be substantial, but the economic cost could be at least partly offset by use of commercial species in buffers, an approach which is likely to hasten adoption. Woody crops, especially short cycle coppice with its strong nutrient-stripping potential due to regular harvest, would appear to be well suited to this purpose. With the rapid economic development in China since the 1980s there has been a surge in expansion of arable agriculture on steep land (often exceeding 25°) in many provinces.41 In response to severe erosion, hedgerow intercropping systems are being developed to control erosion and improve land productivity. Sun et al.41 report that farmers are greatly motivated by species that deliver these benefits but also deliver direct economic return. There are many options for return, including local fuel wood supply. Perhaps the major historic use of trees within agriculture has been for shelter from wind for erosion control as well as stock and crop protection. With the intensification of modern agriculture and more confidence in agronomic management there appears to be a declining interest in using trees for shelter. This comes from what was historically a low level of uptake anyway. Brandle42 calls for better understanding of this shortfall in adoption. Cleugh et al.43 indicate the likely key issue, that is, the total costs of windbreaks (establishment, competition zone causing adjacent crop suppression) are not sufficiently offset by the protection gains provided. The only option is to seek more revenue directly from the trees. Niche
Complementary Benefits of Woody Crops;Concepts and Examples “Agroforestry” and “farm forestry” are synonymous terms for the use of forestry or woody crops within agriculture. This practice is often motivated by the benefits of using woody crops in ways that are complementary to agriculture, that is, where the mixed system can achieve better performance than either component alone.31 To achieve complementarity, woody crops will usually be integrated into the agricultural system in carefully designed small blocks, spatial arrays (belts, buffer strips) or temporal sequences.32 A wide range of species may be used, including conventional forestry species (for sawn timber or pulp) or short cycle coppice for wood products and bioenergy.19 A key driver of the scientific interest in complementarity is the concept that a farming system that integrates woody crops with conventional agricultural crops/pasture can more fully utilize the basic resources of water, carbon dioxide, nutrients, and sunlight, thereby producing greater total biomass yield.33 Such complementary performance will be the net result of enhanced resource use minus the impact of competition between the woody and agricultural components.34 It has proved difficult to rigorously demonstrate complementary benefits in terms of local scale total biomass yield.35,36
(37) Pretty, J. Philos. Trans. R. Soc., B 2008, 363, 447. (38) Mitsch, W. J.; Day, J. W.; Gilliam, W. J.; Groffman, P. M.; Hey, D. L.; Randall, G. W.; Wang, N. BioScience 2001, 51, 373. (39) Dosskey, M. D. Environ. Manage. 2001, 289 (5), 577. (40) Schultz, R. C.; Isenhart, T. M.; Simpkins, W. W.; Colletti, J. P. Agrofor. Syst. 2004, 61, 35. (41) Sun, H.; Tang, Y.; Xie, J. Agrofor. Syst. 2008, 73, 65. (42) Brandle, J. R.; Hodges, L.; Zhou, X. H. Agrofor. Syst. 2004, 61, 65. (43) Cleugh, K.; Prinsley, R.; Bird, R. P.; Brooks, S. J.; Carberry, P. S.; Crawford, M. C.; Jackson, T. T.; Meinke, H.; Mylius, S. J.; Nuberg, I.; Sudmeyer, R. A.; Wright, A. J. Aust. J. Exp. Agric. 2002, 42, 649.
(31) Bartle, J. R. Chapter 16: Integrated production systems. In: Agroforestry for Natural Resource Management; Nuberg, I.; George, B.; Reid, R. Eds.; CSIRO Publishing: Collingwood Vic., 2009; p 360. (32) Stirzaker, R. J.; Cook, F. J.; Knight, J. H. Agric. Water Manage. 1999, 39, 115. (33) Sanchez, P. A. Agrofor. Syst. 1995, 45, 5. (34) Cannell, M. G. R.; Van Noordwijk, M.; Ong, C. K. Agrofor. Syst. 1996, 34, 27. (35) Ong, C. K.; Leakey, R. R. B. Agrofor. Syst. 1999, 45, 109. (36) Garcia-Barros, L.; Ong, C. K. Agrofor. Syst. 2004, 61, 221.
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Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438 change and salinization, and especially in Western Australia, this is eroding its natural resources capital. One of the options to improve sustainability of these systems is to complement the annual agricultural crop and pasture species with commercially attractive tree (or woody) crops to achieve greater water use and moderate the hydrologic change. Conventional forestry species used in higher rainfall areas are not commercially viable in this rainfall zone,46 and there are no existing species that would be viable in the wheatbelt on the necessary scale. Hence new woody crops had to be developed. The diverse and vigorous native mallee eucalypt species that were a prominent component of the original native vegetation were an obvious prospect for domestication as short cycle coppice crops. Over the past two decades considerable progress has been made in developing mallee to the stage where it might take a role as a commercially viable component of more sustainable agricultural systems.47,48
products or local operations do not have the scale to make a difference. Bioenergy has the potential to provide large scale markets, and in spite of the lower height of trees subject to regular harvest, to provide useful collateral shelter benefits. Woody crops in agricultural systems can make an important contribution to nature conservation by providing habitat for native plants and animals; and by ameliorating the impacts of agriculture on natural ecosystems, for example, by minimizing herbicide and fertilizer drift, and by managing the downstream impacts of excess water and solutes.44 These benefits come as a consequence of any woody crop planting, but they can be enhanced if included in system planning and design. Another major contribution that tree crops can make is to modify the water balance and hydrology of agricultural catchments.45 This provides opportunity to manage streamflow volumes, stream solute and sediment loads, groundwater accumulation, water-logging, and water erosion. Southern Australia has major problems with groundwater accumulation in its mostly very flat agricultural landscapes, and a major investment has been made in developing woody crops to help control this problem.46-48 The next section is a brief case study of one such crop.
Mallee Industry Design and Progress Development of mallee began in the early 1990s.47 It was conceived as a pioneer woody crop industry for the wheatbelt, initially to be based in Western Australia. It was recognized at the outset that any new industry would have to be commercially attractive to be adopted on the scale necessary to make a useful contribution to salinity control. Australian farmers have survived a generation of decline in real value of their crops with little government support (4% of gross farm income) compared to US farmers (20%) and EU farmers (35%).52 Salinity benefits have a large external (off-farm) component and can take 20-30 years to be realized. From the farm business perspective, the discounted present value of the internal indirect benefits (e.g., on-farm salinity control) is too little to make much of a contribution to helping finance investment in remedial works. Hence, from the farmers perspective, mallee development had to be driven on its commercial merits. On the other hand, the substantial public investment in mallee research and development could be seen as recognition of the potential value of external environmental benefits. Mallee eucalypts were chosen because they are a diverse and vigorous group of species. Being native species, the genetic resources are readily accessible, and species adapted to all soil and site types are available. Mallees have outstanding coppicing ability and can be harvested on a 3-7 year cycle indefinitely. The range of species being developed was selected to give coverage across all major soil types. Extensive collection of germplasm has been undertaken, and breeding and seed production programs are well advanced. Many mallee species have a high concentration of oil (called eucalyptus oil) in their leaves. Eucalyptus oil has small traditional markets but also has potential for large-scale industrial use.53,54 Eucalyptus oil makes up ∼1% of green biomass and, in contrast to the traditional industry, it was never considered likely to generate sufficient revenue to alone drive a modern industry. Hence, higher value uses for the wood fraction, and bioenergy use for the residues, were also important objectives.
Development of Woody Biomass Crops in Australia The motivation for the substantial public investment to develop woody biomass crops for dryland agriculture in Australia over the past couple of decades has been primarily environmental. Extensive agricultural development in Australia commenced in the late 1800s. Since then some 50 Mha of low relief, mainly winter rainfall (300-600 mm/year) native woodland and shrub-land in the southern half of the continent has been converted to shallow-rooted, annual winter-growing crops and pastures. This region is commonly known as the wheatbelt. The change in vegetation cover has reduced evapotranspiration by a small but significant amount. Due to low relief and poor drainage, surplus soilwater is accumulating in groundwater systems, mobilizing previously stable stored salts and discharging saline water into valleys and streams.49,50 It is estimated that 5 million ha of land has been damaged by salinity so far, and this could more than double over several decades until a new hydrologic equilibrium is established. Damage is not confined to land and water resources. Hydrologic change and salinity on whole river systems is also causing loss of biodiversity, amenity, increased flood risk, and damage to infrastructure.51 The commercial success of wheatbelt agriculture has come at the cost of significant hydrological (44) Smith, F. P. Landscape Urban Plann. 2008, 86, 66. (45) Stirzaker, R.; Vertessy, R.; Sarre, A. Trees, Water and Salt, an Australian Guide to Using Trees for Healthy Catchments and Productive Farms. Joint Venture Agroforestry Program: Canberra, 2002; p 159. (46) Bartle, J. R.; Cooper, D.; Olsen, G.; Carslake, J. Conserv. Science West. Aust. 2002, 4, 96. (47) Bartle, J. R.; Shea, S. R. Proceedings of the Australian Forest Growers 2002 National Conference. Private Forestry ; Sustainable Accountable and Profitable; 2002, pp 243-250. (48) Bartle, J.; Olsen, G.; Cooper, D.; Hobbs, T. Int. J. Global Energy Issues 2007, 27 (2), 115. (49) George, R. J.; McFarlane, D. J.; Nulsen, R. A. Hydrogeol. J. 1997, 5, 6. (50) Clarke, C. J.; George, R. J.; Bell, R. W.; Hatton, T. J. Aust. J. Soil Res. 2002, 40, 93–113. (51) National Land and Water Resources Audit. Australian Dryland Salinity Assessment 2000. Extent, Impacts, Processes, Monitoring and Management Options. National Land and Water Resources Audit: Canberra, ACT, 2001; p 129.
(52) Productivity Commission. Trends in Australian Agriculture; Commonwealth of Australia: Canberra, ACT, 2005; p 170. (53) Coppen, J. J. W. Eucalyptus ; The Genus Eucalyptus; Taylor & Francis: London, 2002; p 183. (54) CSIRO Molecular & Health Technologies. Australian Provisional Patent Application No. 2009903333. Cineole 2009. Patent applied for.
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Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438
The design of production systems sets out to replicate what Australian wheatbelt farmers are accustomed to in grain production, that is, large scale, low labor input, advanced technology, and bulk handling systems. For example, analysis of harvest and supply chain options indicates that a mobile, large-volume chipper-harvester is required to create a single raw product stream for delivery to the processing center at >60 tons/hour. To meet its challenging operating cost target, the supply chain should be continuous so that there is no temporary storage involving an unload/reload step from harvester to the processing plant.55,56 Agronomic development has been undertaken as part of operational scale exploratory planting by farmers. Some 20% of Western Australian wheatbelt farmers (∼1000 farmers) have collectively planted more than 12 000 ha of mallee mostly in narrow belts (parallel or contour) across crop land designed to capture surplus water from the adjacent annual crops and pasture areas. Growers quickly found that dispersed mallees tolerated sheep grazing, and even with low management input, did not require fencing, thus avoiding a major cost. Growers formed a representative industry development group (Oil Mallee Association) and have prepared a code of practice and an industry development plan.57,58 The preparedness of farmers to undertake large-scale test plantings attracted the interest of potential biomass processors. Feasibility investigation was first undertaken by Enecon in 2000.59 This showed that electricity generation alone would not be commercially viable, even with the then modest level of renewable energy credits. However, with integrated processing of mallee biomass to produce a range of products it was feasible. Enecon investigated three products;eucalyptus oil, activated carbon, and electricity;and showed that each revenue source was critical to commercial viability. They used a biomass feedstock price that made mallee competitive with other wheatbelt agricultural options, and therefore attractive to growers. Following the feasibility study, a 20% scale demonstration plant was constructed and conducted operational testing and process refinement during 2006. Commercial development was delayed, apparently awaiting passage of legislation in the Commonwealth Parliament. The national Renewable Energy Target (RET) scheme has now been passed and will expand the previous Mandatory Renewable Energy Target (MRET) by over four times to 45 000 GW 3 h by 2020.60 This scale of renewable energy demand is likely to make bioenergy projects prospective in areas of the State grid where additional base-load power is required. Integrated processing is an important conceptual advance. It allocates each biomass fraction (leaf, bark, woodchip, and twig) to its highest value product option within an efficient
processing facility. Hence, research has been undertaken to look at higher value uses for the woodchip fraction, for example, panel board products, fiber-wood composites, metallurgical charcoal, biochar for soil amendment, and carbon products. Similarly, eucalyptus oil appears well suited to development for industrial solvents and as biomaterials feedstocks.53,54 Potential Yield and Scale of Mallee Biomass Production in the Australian Wheatbelt. In the wheatbelt, pan evaporation ranges from 1600 to 2800 mm/year across latitudes 36-28°S, exceeding rainfall (range 300-600 mm/year) by a factor of from 3 to 9. In this climate water is a major limiting factor for the growth of perennial woody crops. On the other hand, annual crops and pastures with shallow root systems and winter growth cycle are often not able to fully utilize the winter rainfall and are only able to use a small proportion of summer rain that enters soil storage. This opens the opportunity to design woody crop planting layouts to capture at least part of that surplus. Indeed, the extent of capture of that surplus will determine yield and the size of the contribution to salinity control. The issue of design for optimum water capture is therefore crucial. Optimum designs will involve the use of long narrow belts planted parallel or on the contour with the conventional annual crops and pastures in the “alley” in between. On suitable soils by age 6-8 years, mallee belts create zones of extensive vertical (>10 m) and horizontal (up to 20 m) exhaustion of available soilwater thereby allowing a narrow belt to create a substantial soilwater sink.61,62 Belts can therefore be designed to passively intercept local surface water runoff, or to receive actively harvested water from nearby high runoff locations. Existing biomass yield models need to be coupled with local runoff generation models to improve yield prediction capability. Furthermore, existing biomass yield models do not deal adequately with the impact of coppicing under various seasons and frequencies of harvest. A conceptual model was developed to examine the availability of surplus water in the wheatbelt, the increase in yield this could deliver and the extent to which extra water would enable economically viable yields to be achieved.63 This indicated that narrow belts and wide alleys with only about a 10% proportion of belts would be near the economic optimum. This analysis was used to make first estimates of the total potential mallee biomass production across the Australian wheatbelt.48 Energy Balance of Mallee Biomass Production Systems. Wu et al.17 analyzed the balance of energy inputs and outputs in growing, harvesting, and delivering mallee biomass to a central processor. The assessment was made for a term of 50 years, where the first harvest or sapling crop takes 5 years to reach harvestable size and subsequent coppice crops are taken every 3 years. Over the 50 year production period there is one initial sapling crop (at 5 years) and 15 coppice crops (over 45 years). All activities occurring during the mallee production period that involve direct nonrenewable energy inputs (liquid fuels and lubricants, heat, electricity) and/or indirect energy inputs (fertilizers, agrochemicals, tractors, agricultural machinery, transport equipment, labor, capital) were
(55) Giles, R. C.; Harris, H. D. Developing a biomass supply chain for new Australian crops. In Short Rotation Crops for Bioenergy; proceedings IEA Bioenergy Task 30 conference, Tauranga, NZ, December 1-5, 2003. (56) Yu, Y.; Bartle, J.; Li, C. Z.; Wu, H. Energy Fuels 2009, 23, 3290. (57) Oil Mallee Association. Mallee Cropping Code of Practice. Joint Venture Agroforestry Program: Canberra, 2003; p 44. (58) Oil Mallee Association. Oil Mallee Industry Development Plan for Western Australia. Forest Products Commission: Perth, 2008; p 103. Available at http://www.fpc.wa.gov.au/content_migration/_assets/documents/industry_plans/oil_mallee_idp.pdf [Accessed June 2009]. (59) Enecon Pty Ltd. Integrated Tree Processing of Mallee Eucalypts, Publication No. 01/160; Rural Industries Research and Development Corporation: Canberra, 2001; p 81. Available at http://www.rirdc.gov.au/reports/ AFT/01-160.pdf [Accessed: June 2009]. (60) Department of Climate Change. Legislation and the Renewable Energy Regulator. Available at http://www.climatechange.gov.au/renewabletarget/legislation.html [Accessed Aug 2009].
(61) Robinson, N.; Harper, R. J.; Smettem, K. R. J. Plant Soil 2006, 286, 141. (62) Sudmeyer, R. A.; Goodreid, A. Ecol. Eng. 2007, 29, 350. (63) Cooper, D.; Olsen, G.; Bartle, J. R. Aust. J. Exp. Agric. 2005, 45, 1369.
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Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438 Table 3. Standard Operating Assumptions for the Economic Analysis in $Australian (2009)
parameter project duration belt layout establishment cost annual management cost harvest regime yield above ground yield below ground competition loss factor harvest and delivery delivered biomass price price for carbon sequestered in root biomass equivalent annual value (EAV) from agriculture overall management of mallee crop and supply chain emissions limits on agriculture
standard value 50 years. two row belts occupying 7m width with alley width of 72m to give a proportion of paddock area occupied of 8%. $800/ha of belt area. $5/ha/year. 5, 3, 3; i.e., first harvest at age 5, coppice cycle every 3 years. 50 green tons/ha of belt area every harvest. below ground biomass grows at 50% of above ground biomass to first harvest. There is a 30% loss of root biomass on harvest, followed by a net 7.5% gain by the following harvest. 0.8; i.e., this is the loss of production in the paddock immediately adjacent to the mallee belt as a proportion of the belt area. $26/green ton consisting of harvest, on-farm haulage and delivery to processing point 50 km away. $45/green ton (includes all production and supply chain costs). projected to rise from $25/ton CO2-e in year 1 to $115/ton at year 50.65 No formal commitment to emissions control has yet been legislated. $164/ha/year; i.e., the annualized NPV from agriculture, derived from a cash flow configured to reflect seasonal variability. to form a consolidated supply requires an estimated 20% of the delivered biomass price given above. no emissions limits are currently applied to agricultural practice in Australia.
Figure 2. Cumulative undiscounted cash flow per ha for the mallee belt, the mallee belt with carbon sequestration revenue from root growth, and for the conventional agriculture.
specified. For each input, the energy amount was converted back to a common base, that is, the equivalent nonrenewable primary energy required to supply the energy used. The energy output is the primary energy contained in all mallee biomass components, that is, wood, bark and twig, and leaf. The energy ratio (output of energy in biomass/input of energy in production) was found to be 41.7. This high ratio reflects the strong competitive position of coppice crops in energy capture compared to annual or other short-lived agricultural crops. Coppicing avoids regular replanting inputs after every harvest. A high energy ratio is also favored by the complementary position mallee occupies with annual agricultural crops, that is, higher mallee yields can be achieved through capture of surplus water and nutrients. Economics of Mallee Biomass Production. A model was constructed to demonstrate the economic performance of a standard paddock with a dispersed array of two-row mallee belts occupying ∼8% of the paddock compared to the same paddock under the conventional annual crop and pasture agriculture. The location is the upper great southern region of the Western Australian wheatbelt where the rainfall is 450-500 mm/y. The discounted cash flow technique was used to calculate and compare the cash flows of conventional agriculture and mallee crop. Net cash flows are the difference between cash inflows (derived from yield and price of products) and cash outflows (operational expenditures on establishment,
management, harvest, and transport). To compare the two different options it is necessary to use the same project life for each. A period of 50 years was chosen to provide time for the value of the long-term mallee investment to become apparent. The agricultural crop rotation was assumed to be repeated for the same duration using the constant chain of replacement assumption.64 To facilitate comparison of the two options the net present value (NPV) of the discounted cash flow of the options was calculated to derive the equivalent annual value (EAV).64 EAV is the annualized equivalent of NPV. The analysis used the standard operating inputs and assumptions given in Table 3. Note that all values in Table 3 are in $Australian. Under these assumptions the equivalent annual value (EAV) of agriculture is projected to be $164 over the 50 year duration of the analysis. Figure 2 shows the cumulative undiscounted cash flows for both the options; undiscounted cash flow is used here for clarity and ease of presentation. It shows agricultural cash flow projection incorporating variability arising from agricultural crop rotations, seasonal change in yields, and market price fluctuation. It also shows the cumulative cash flow per ha for mallee belts alone. There are two mallee cash flows (64) Peirson, G.; Brown, R.; Easton, S.; Howard, P. Business Finance, 8th ed; McGraw Hill: Sydney, 2002; pp 164-167.
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Energy Fuels 2010, 24, 2–9
: DOI:10.1021/ef9006438
Figure 3. Periodic yield of above-ground mallee biomass over time for the 5, 3, 3 harvest cycle and the pattern of below ground biomass accumulation over time both in green tons/ha. Table 4. Sensitivity to a (10% Variation in the Major Variables Expressed in the Form of Change in the EAV EAV parameter
standard input
standard
þ10%
-10%
above ground yield at each harvest cost of harvest and delivery to processing center biomass selling price carbon price
50 green tons $26/green ton $45/green ton $20-115 over 50 years
$335
$374 $299 $395 $348
$295 $370 $274 $321
presented: one with revenue being generated by harvest of above-ground biomass, and the second with the addition of revenue generated by carbon sequestered in below-ground biomass. Note that cash flow from the mallee belts does not exceed that from agriculture until about year 12, and from then on it remains ahead. Note also that revenue from belowground carbon sequestration is useful but not critical to the viability of mallee crops. When expressed in terms of NPV (discounted at 7%/year over the 50 year term) the agriculture option has a NPV of $2269/ha, mallee belts with no carbon is $2706, and mallee belts with carbon is $4617. The same results expressed as EAV are agriculture $164/ha; mallee belt area without belowground carbon revenue is $196/ha, and mallee (with carbon) is $335/ha. Although the cash flow of mallee belts appears strong when expressed on a per ha basis, belts only constitute 8% of the paddock area, and so this would be reflected in only a modest improvement in whole paddock cash flow. The revenue from carbon sequestered below ground was assumed to start low ($A25/t CO2-e) and rise continuously over the 50 year period to $115/t as foreshadowed in the Garnaut Review.65 This price trajectory was indicated as necessary to achieve an atmospheric CO2-e of 550 ppm under the standard technology assumption. Carbon revenues are assumed to be accounted on an annual change in stocks basis. The carbon revenues expressed as EAV contribute $139/ha to the overall mallee belt EAV, or expressed as part of annual biomass revenue (i.e., $139/ha/17 green tons/ha/y) it delivers an additional $8/t. Figure 3 shows how above ground mallee green biomass varies over time within the 5, 3, 3 harvest cycle. It also shows how root biomass varies over time. Root biomass accumulates, but its trajectory reflects the harvest cycle because some
30% of root biomass is lost at each harvest, but is restored and expanded within each harvest cycle. Note that the amplitude of the root loss/recovery cycle increases over time because this is likely to be necessary to maintain the health of the root system and the productivity of the crop.66 Table 4 shows the results of a sensitivity test of some key parameters as reflected in change to the EAV. Biomass selling price is the most sensitive parameter followed by yield and supply chain costs. These parameters are major targets for further research. Yield and supply chain design are the subject of current major research and development projects. Conclusion Continuing productivity improvement in global agriculture and the quickening decline in global population growth rate may make large areas of agricultural land potentially available for alternative uses over the next half a century. Bioenergy is one the few product options with the potential market scale to fully utilize this opportunity. However, it is generally expected that bioenergy will have problems winning market share in competition with other renewable energy options. Careful development of on and off-farm benefits of bioenergy crops may demonstrate that conflict with food production is minimal; that the overall cost of bioenergy from woody biomass feedstocks is quite competitive with other renewables; that bioenergy can make a major contribution to a more productive and sustainable agriculture; and that a wide range of environmental benefits may be delivered by the proposed systems. Acknowledgment. The concepts and activities reported here have been supported by the Natural Resources Branch in the Department of Environment and Conservation and by the Future Farm Industries Cooperative Research Centre. The authors thank close colleagues and reviewers for critical comment on drafts of this paper.
(65) Garnaut, R. The Garnaut Climate Change Review: Final Report; Cambridge University Press: Melbourne, 2008; p 617.
(66) Wildy, D. T.; Pate, J. S. Ann. Bot. 2002, 90, 185.
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