Biomass refers to total dry weight of living material expressed in terms of volume or area. This organic material can be harvested as a source of energy. Plants store energy from sunlight in their various parts, which can be accessed through several technologies. Plant biomass can be burnt to generate heat energy or electricity, converted to liquid and transportable fuels, or used as a feedstock for the production of chemicals. It can also be used as compost or green manure, and converted into building materials, fiber, or animal feed. Plants are the main source of biomass for energy, with crops that produce the greatest quantity of bulk material in the shortest possible time the most useful. The maximum biomass yield for energy crops is typically around 30 tonnesha-1 (White and Plaskett, 1981).

Biomass crops for energy have a number of disadvantages compared to fossil fuels, including a relatively modest thermal content, an often high moisture content that inhibits combustion, and a low density and high volume that necessitate large-scale equipment for handling and combustion. Procedures to improve the properties of biomass primarily involve drying and compaction. Biomass has advantages over fossil fuel in that it is renewable, releases less carbon dioxide into the atmosphere, and is readily obtainable, inexpensive, and not subject to unpredictable shortages or steep cost increases (White and Plaskett, 1981). As with all alternative energy strategies, the economic feasibility of energy crops depends on the cost of competing conventional fuels. As fossil fuel prices increase, the economic viability of plant biomass options is enhanced.

Jerusalem artichoke, with its rapid growth rate and ability to grow on marginal land, has great potential as a source of biomass for energy. It can yield well over 30 tha-1 under favorable conditions, is efficient in terms of water use, is a low-input crop with minimal external production costs, is rich in polysaccharides, and is among the group of plants that produce the highest total dry matter yield per hectare (Dambroth, 1984). Biomass production usually involves aerial plant parts, although all parts of Jerusalem artichoke can be utilized. The aerial parts are a feedstock for direct combustion and biogas production, while the tubers and stalks are used for alcohol production. The fructans in Jerusalem artichoke are temporarily stored in the stalks or stems prior to being translocated to the tubers. Therefore, harvesting aerial parts when they contain abundant sugar, before tuber filling occurs, is the best approach if they are to be used for alcohol or biogas production. However, cutting the tops can impede tuber formation, thereby reducing the potential of Jerusalem artichoke as a multifunctional crop (Faget, 1993). Nevertheless, studies have shown that given the right timing of cutting, both aerial and belowground parts of Jerusalem artichoke can be utilized (e.g., Stauffer et al., 1981; Rawate and Hill, 1985). As plants can only assimilate a certain amount of carbon during a given period, whether tops, tubers, or both are ultimately harvested may make relatively little difference in terms of dry matter biomass in the long term.

A series of field trials in Europe in the late 1980s assessed the potential of Jerusalem artichoke as a multifunctional (food and nonfood) crop. Yields and growth characteristics were recorded from Ireland to Romania, and from Denmark to Spain and Italy, with the highest yields occurring in irrigated crops in Southern Europe (Grassi and Gosse, 1988). However, changing climatic conditions will influence energy crop distribution in Europe during the 21st century (Tuck et al., 2006). In a survey of 26 promising energy crops, Tuck et al. (2006) analyzed crop requirements against climate change models. Crop requirements for Jerusalem artichoke, for instance, included maximum and minimum rainfall of 1600 and 500 mm, and May to September temperatures averaging between 8 and 25°C. In 1990, most Jerusalem artichoke in Europe was grown in the latitudes 45 to 54° and 55 to 64° North. However, by 2050-2080, all the climate models tested predicted a substantial decline (up to 31 to 45%) in Jerusalem artichoke cultivation in latitudes 45 to 54° North (France and Germany), a small (5 to 15%) increase in cultivation in latitudes 55 to 64° North, and a large increase (up to 40 to 60%) in cultivation in the more northerly latitudes of 65 to 71° North. In this latter area, comprising Scandinavia and northern Russia, suitable land for Jerusalem artichoke cultivation will increase from 10% to around 80% of total cultivable land area. National Resources Canada is also modeling how climate change is likely to affect the range of Helianthus tuberosus in North America. In the models, by 2041 to 2070, the range has extended northward to Newfoundland (around St. John's) and westward over a large area of Alberta (centered on Edmonton); by 2071 to 2100, some areas of southern Alaska become suitable for growing Jerusalem artichoke (Canadian Forestry Service, 2006).

The cultivation of Jerusalem artichoke on marginal land for bioenergy can potentially be combined with a bioremediation function. The closely related sunflower (Helianthus annuus L.), which has a similar high biomass and rapid growth rate, is known to effectively accumulate cadmium (Cd), copper (Cu), lead (Pb), manganese (Mn), and nickel (Ni) from water contaminated with heavy metals (Brooks and Robinson, 1998; Dushenkov et al., 1995). Sunflower also removes cesium and strontium from radioactive environments, as shown in field tests around the damaged Chernobyl nuclear facility in Ukraine (Cooney, 1996; Dushenkov et al., 1999); after 10 days, roots of potted sunflowers had taken up so much radioactivity from comtaminated pools they could not be removed from the exclusion zone (Coghlan, 1997). Experimental studies have confirmed the considerable ability of Jerusalem artichoke to accumulate heavy metals, and its potential as a tool in the reclamation of land contaminated with heavy metals (Antonkiewicz and Jasiewicz, 2003; Antonk-iewicz et al., 2004; Jasiewicz and Antonkiewicz, 2002). The metal content of Jerusalem artichoke tissue increases with the level of soil pollution with heavy metals. In descending order, the effectiveness of Jerusalem artichokes for accumulating heavy metals was Cd, Zn, Ni, Cu, and Pb (Antonkiewicz and Jasiewicz, 2003). Its potential as a combined energy crop and bioremediation tool, however, may be reduced by yield reductions in soils containing high levels of heavy metals (Jasiewicz and Antonkiewicz, 2002).

The environmental impact of growing energy crops over large land areas should be a consideration when assessing their potential. In Germany, 10 energy crops, including Jerusalem artichoke grown as a perennial (40,000 plantsha-1), were assessed on sandy soil under four fertilization regimes. Jerusalem artichoke was found to be a relatively good absorber of Pb, while having a relatively benign impact on soils and the environment compared to other energy crops. For instance, phosphorus levels in Jerusalem artichoke tops (haulms) were relatively low (0.05 to 0.15% dry matter), and the crop therefore does not require much phosphorus fertilizer, which is beneficial in terms of water eutrophication. Yields for Jerusalem artichoke tops were relatively low, however, in this study (4.3 t dry matterha-1), giving an energy balance of 62 GJha^year-1. It was also noted that the stability of the stems diminished over the years when grown as a perennial, making the tops harder to harvest. Higher top yields occurred if the tubers were not harvested (Scholz and Ellerbrock, 2002).

Harvesting the tubers can lead to potential problems, as incomplete harvesting can cause crop resurgence in the following season, which makes Jerusalem artichoke difficult to fit into crop rotations. Better harvesting methods or control of volunteer plants needs to be developed if Jerusalem artichoke is to become an important biomass crop in rotations (Faget, 1993). However, when cultivated as an energy crop, Jerusalem artichoke has increasingly been grown as a perennial turning a potential harvesting problem into a virtue.

A pressing research need is the development of modern cultivars with improved characteristics for biomass and energy. In a Canadian study, a wide variation in forage composition was found among accessions, suggesting that composition could be readily improved through plant breeding (Stauffer et al., 1981). To fulfill its potential as an energy crop, Jerusalem artichoke will also require government support, for example, in the form of tax exemptions and research grants.

The total cost of producing biomass from a model tall broadleaf crop (sunflower) was estimated as 12.7 U.S.St-1, given a whole plant yield of 15.0 t dry matterha^year-1. This was cheaper than the cost estimates for any other crop type, including tall grass (maize, 19.1 St-1), short broadleaf (sugar beet, 77.1 St-1), and legume (alfalfa, 20.9 St-1) (Klass, 1998). Estimates for a Jerusalem artichoke biomass crop in Italy suggested that farmers would need to receive from 18 to 47 Ecut-1 (1990 prices) for tubers to gain an income comparable to more traditional energy crops (Bartolelli et al., 1991).

The two principal ways of obtaining energy from biomass are thermal (direct combustion) and biological (the conversion of organic matter to biofuel through microbial action). Biomass is also playing an increasingly important role as a feedstock for organic chemicals and materials. The utilization of inulin from Jerusalem artichoke as a feedstock for a range of industrial chemicals has been described in Chapter 5. The combustion and biological conversion of Jerusalem artichoke to produce energy is considered below.

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