Dames Rocket is a showy, spring perennial wildflower with large, loose clusters of fragrant white, pink, or purple flowers that bloom in April and May on flowering stalks about 1 m high. This member of the mustard family has flowers with four petals. Many seeds are produced in long, narrow fruits. The leaves are oblong, sharply toothed, and alter­nately arranged. Leaves decrease in size as they ascend the stem.

This plant usually grows in moist soil and does best in sun condi­tions. The seed is commercially available since it is often planted orna­mentally and included in many wildflower seed mixes.

Dames Rocket dies off and dries out by early August. It is one of the earliest of the sclerified stalked plants that is ready to harvest. The plant grows to over 1 m, and the stem diameter is about 1.1 cm. The XPR for this plant is a lowly 0.22, with a correspondingly low expected yield.

Goldenrod (Asteraceae Solidago) (Fig. 4)

Goldenrod is a perennial wildflower with a multitude of varieties. It is the state flower of Alabama, Nebraska, and Kentucky. Most species have feathery, rich sprays of florets atop sturdy stems. These small clus­ters of yellow flowers are prominent features of the landscape in Septem­ber and October, and signal the end of summer. Goldenrod blooms late and dries down slowly, probably owing to the protective waxy epidermis of its stem.

Goldenrod is an erect perennial with simple, alternate, toothed or smooth-margined leaves. Its dried leaves have been used for a tealike bev­erage by the Indians.

There are many varieties, including early and Canadian. All enjoy full sun and a variety of soil conditions. In general, they present no diffi­culties in growing. The plant propagates itself by both a spreading root system and seed.

Fig. 5. Wild sunflower is much different from domestic sunflower.

It can grow to 2 m with a stalk that is about 0.8 cm in diameter. In the stem cylinder, the XPR is 0.78 and it has a density that rates well.

Some varieties of late goldenrod (Canadian) are late blooming and even later drying down, so they may not be ready for harvest until almost December. There is a misperception that goldenrod causes hay fever; it is actually the pollen of ragweed and grasses that causes this. Goldenrod’s pollen grains are relatively large, heavier than air, and therefore are carried off by flies, bees, butterflies, even ants or birds, but not by the wind.

Annual Sunflower (Asteraceae Helianthus) (Fig. 5)

To most people, sunflower conjures an image of a domestic plant with a large stalk crowned by a single large flower. The wild sunflower, or annual sunflower, however, exhibits a branched growing form with numerous smaller flowers at each branch tip. The average diameter of wild sunflower is about 1 cm, unlike cultivated forms, which commonly reach 30 cm.

The stem is erect, columnar at the base and branched at the top. The leaves are alternate, simple, rough, hairy, and ovate or heart-shaped with toothed edges. The heads are showy, with yellow to orange-yellow ray flowers and brown or dark reddish-brown disk flowers. Sunflowers begin to grow in early June, flower in August and September, and mature seed and die in late September.

Wild sunflower, or common sunflower, is an annual, reproducing by seed. The seeds are shaped like the commercial sunflower seeds bought in stores, but much smaller and spread by the wind.

These plants can grow to 3 m with a stalk that is about 1.1 cm in diameter. Stem construction consists of a moderately waxy, dark red epi­dermis. The xylem cylinder has an XPR of 0.46. Xylem material has a density of 540 kg/m3, which is about half that of pine wood. The pith is a solid spongy inner core that appears to be resilient to rot for many months.

Methods

Table 1 is important to the analysis of SSPs because it establishes a basis for future evaluation of the fuel source. Yet, much of the information is subject to growing conditions such as soil, water, and amount of compe­tition with other plants. Because there are no cultivated acres of these plants, the projected yields listed in Table 1 are based on stalk weights, which were measured, and growth density (stalks/m2), which were estimated. The estimations came from grid layouts made in productive parcels of wild — grown fields. They represent what I feel to be a conservative estimate of what densities can be achieved in cultivation.

The material density was determined from stalk weight and XPR based on the assumption that the stalk is a composite material of hard biomass and soft pith. The weight, but not the volume, of the pith was neglected:

(avg stalk height x cross-sectional area

Density = Avg stalk weight/

of stalk — cross-sectional area of pith)

Projected yield (PY) was determined using the following formula:

PY = (density x biomass stalk volume x no. of stalks/acre)

PY (t/acre) = Mat density x Avg Stalk Height x n x diam2 (1 — 1/XPR2)/4 /2.2/2000

Analysis

It is not the objective of this article to analyze the plants in the set of SSPs to determine which would be the most acceptable as an energy crop. One reason for this is that SSPs, as a fuel source, are a variety of plants rather than just one. As a variety, they have much more flexibility. It is expected that power plants fueled by SSPs will actually have farm contracts for sev­eral of the species within the set. Some species will be harvested and deliv­ered early in the season and others late. This facilitates the storage of the fuel since the window of harvest can be up to 6 mo.

In addition, some SSPs dry down better than others. Having a variety of moisture conditions may be of benefit to the burner. Burning some green material with fully dried material is often the best solution for determining burner feed rates and utilizing the full combustion chamber.

Another reason for keeping all the varieties in the SSP set is that some grow better in certain soils and climates. This is not to say that the nine species identified here will all be viable energy crops, or that other species will not be added. For example, it is hard to imagine any farmer wanting to work with field thistle, no matter how much protective clothing the farmer has. Yet, thistle shows some signs of having the capability of delivering high yield, and, therefore, it should stay a member of the list awaiting further research.

Cocklebur may not be an acceptable member because it is a Class C noxious weed in many parts of the United States. Couple this with the fact that it does not have good physical characteristics for a biofuel and cockleburris place on the SSP list is precarious.

Some may argue that Evening Primrose is not a true candidate owing to its biannual nature. However, its SSP harvestable material is the densest of all the members of the list, as if the additional year that it takes to mature may have been well spent. More research is needed to determine the den­sity at which it can be planted, and what effect the first-yr plant will have in occupying space in the field.

A further argument for keeping active all members of the SSP list is that there is some interest in targeting acreage that is currently in govern­ment "set-aside" programs as sources of the biomass material. In this case, without preparation of the field, the herbaceous stalked material may sim­ply grow wild on the acreage. If this is to be the case, it may not be possible to select the actual plants that will be harvested, and they may include all members of the list along with grasses and more.

It is also not the objective of this article to compare SSPs as a biofuel crop against other energy crops that are currently under research. The primary reason for this is that there is no competition among energy crops. If biofuel is to become significant in the mix of energy sources, all biofuels will need to be collected. In fact, it can be imagined that if a power plant is built to burn biofuels, it may well prefer a proper mix of woody and herba­ceous materials along with quantities of animal waste.

However, to demonstrate that SSPs deserve their place in the mix of energy crops, one comparison with other biofuel crops should be made. Table 1 gives the physical characteristics of the nine plants in the SSP set. Of particular importance in Table 1 is the last column, which represents the projected yield of each (in t/acre).

With this caveat, Table 1 indicates that the highest yields are >10 dry t/acre. This compares to corn stover at 2.8 t/acre (8), switchgrass at

2.5 t/acre (9), and willow seedling at 6 t/acre/annum (10). Figure 6 puts Table 1 to life, showing the cross sections of each of the SSPs discussed.

Conclusion

SSPs have been introduced as a group of herbaceous plants that should be given recognition as a biofuel feedstock. They should be given their

A

B

C

place in the development of renewable biomass material for direct energy conversion ("directly burnable crop" [11]).

In this article, this new energy crop has been introduced and its ben­efits extolled, in particular, the yield data of Table 1. However, the specifics were done within the economic and time constraints of the grant and are left open for more detailed scrutiny. In particular, the botany and plant physiology of the SSPs need clarification by experts, as do the physical characteristics of Table 1. Further studies are needed to establish heating values for the SSPs and to determine combustion characteristics. Knowl­edge of the cultivation and harvest of these plants must be expanded. The hope is, however, that the set of plants discussed here makes direct burn­able biomass an economically feasible alternative on a broad scale.

Acknowledgments

I wish to thank Gary Haase of The Nature Conservancy at Kitty Todd Nature Preserve in the Oak Openings Region of Lucas Country, OH, for his great insight into the identification and management of the indigenous plants of northwest Ohio. This research was funded by the Ohio Biomass Energy Program.

References

1. OHIO Biobased Fuels, Power and Products Fact Sheet (2003), access to state facts sheet from Website: www. bioproducts-bioenergy. gov/default. asp.

2. Shakya, B. (2000), Directory of Wood Manufacturing Industry of Ohio, Ohio Biomass Energy Program, The Public Utilities Commission of Ohio, Cols, OH.

3. DOE. Department of Energy, Biopower—Renewable Electricity from Plant Material, Website: www. eren. doe. gov/biopower/feedstocks/fe_energy. htm.

4. Teel, A. (1998), Paper presented at BioEnergy ’98: Expanding Bioenergy Partnerships, Madison, WI, October 4-8, 1998 (unpublished).

5. Neuhauser, A., White, R., and Peterson, B. (1996), Paper presented at the 1st Conference of the Short Rotation Woody Crops Operations Working Group, Paducah, KY, September 23-25, 1996 (unpublished).

6. Salisbury, F. and Ross, C. (1992), Plant Physiology, Wadsworth Publishing, Beverly, MA.

7. Rickett, H. (1975), Wildflowers of the United States, McGraw-Hill, New York, NY.

8. Farm Progress Companies. Farm Progress: What Are Corn Stalks Worth?, Farm Progress Companies, Website: www. farmprogress. com/frmp/articleDetail/1,1494,11451+ 19,00.html.

9. Center for Integrated Agricultural Systems. Switchgrass Production for Biomass, Research Brief #51, Center for Integrated Agricultural Systems, University of Wiscon — sin-Madison, Website: www. wisc. edu/cias/pubs/briefs/051.html.

10. Tharakan, A., Isebrands, R. (1998), Paper presented at BioEnergy ’98: Expanding BioEnergy Partnerships, Madison, WI (unpublished).

11. Kamm, J. (1993), Small Farm Today 10(3), 16,17.

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