JRC representatives were advised that sisal could not be successfully grown in Arizona because of its lack of frost tolerance. Bulbils of sisal obtained from the Huntington Botanical Garden were planted in Tucson as a demonstration and they deliquesced and died immediately after temperatures first dropped to 0°C in Dec. 1985. Sisal was selected for domestication because it made good rope, not because it made good paper, but many Southwestern relatives of sisal have frost tolerance and were used by indigenous peoples for cordage products (McLaughlin and Schuck 1991). We jointly decided therefore to screen various members of the Agavaceae to determine if any (1) possessed high-quality fibers and (2) were suitable for production in the temperate climates of the United States.
During 1986 leaf samples were collected from the wild and from several botanical gardens, including the Desert Botanical Garden in Phoenix, the Huntington Botanical Garden in San Marino, California, and the Boyce-Thompson Southwestern Arboretum in Superior, Arizona. The screen included over 100 collections of 62 species from six genera in the Agavaceae: Agave, Dasylirion, Furcraea, Hesperaloe, Nolina, and Yucca. (Many systematists today place Dasylirion and Nolina in a separate family, the Nolinaceae). All leaf samples were sent to James River's Neenah Technical Center in Wisconsin, where they were pulped and made into paper samples that were tested for strength properties.
The best prospects to emerge from the screen were Hesperaloe funifera and Hesperaloe nocturna, both because they had superior fiber characteristics and because they had favorable agronomic traits (McLaughlin 1993). The results of this screening study were never published. In fact, JRC consistently discouraged any disclosure of their participation in the research and development of Hesperaloe. Populations of several species were subsequently resampled and fiber lengths, fiber widths, and cell-wall dimensions were determined at the University of Arizona (McLaughlin and Schuck 1991). Fibers of both Hesperaloe species were longer and thinner than those of any other species examined. Indeed, the length-width ratio of fibers from Hesperaloe funifera is greater than those of most other paper-making fibers and comparable to that of abaca (Musa textilis), the premium paper-making fiber (Table 2).
Based on the results of the 1986 screen, JRC and the University of Arizona selected Hesperaloe funifera and H. nocturna for further research and development. JRC worked on pulping, paper-making, and product development while the University of Arizona worked on various aspects of the agronomy and biology of the plants. Although both Hesperaloe species were not common in nature, we obtained sufficient seed of H. funifera to initiate long-term biomass production studies in 1988 but similar studies could not be started with H. nocturna until 1990.
Biomass production for Hesperaloe funifera has been examined in six 300-m2 plots for seven years. The plots were established at three densities and have been monitored by randomly sampling plants from within the plots at the end of each growing season (McLaughlin 1995). The plots at the highest density (27,000 ha-1) produced a yield of 192 t FW ha-1 after five years (Fig. 2). Very little aboveground growth was observed during the first year. Plots harvested at the end of year 5 regrew slowly in year 6; growth rates in year 7 were comparable to those observed in year 5 prior to harvest.
The relationship between stand density and individual plant biomass is presented in Fig. 3. There was little evidence of competition among Hesperaloe funifera plants in these plots during their first three years, i.e., there was no discernable relationship between stand density and mean plant size. However, effects of crowding were evident in years 4 and 5 after plants flowered and produced their first group of lateral rosettes. The highest density used in this study was achieved using a 61 cm row spacing. Arizona cotton growers most often use 102-cm rows. Hesperaloe planted on 46 cm centers within 102 cm rows would correspond to a density of approximately 21,000 plants ha-1. From Fig. 3 it can be estimated that a stand of 21,000 plants ha-1 should have an average plant size of 8.5 kg FW plant-1 and a standing crop at first harvest of 180 t FW ha-1.
The crop cycle for Hesperaloe is still unclear. Biomass yields can be optimized by delaying the initial harvest until the end of year 5. It appears now that the first reharvest would be at year 8, not year 7 as previously suggested (McLaughlin 1995). A second reharvest might be achieved at year 10 (Fig. 4). Plants should regrow more rapidly after the second cut at year 7 than after the first cut at year 5 because they will have more meristems (rosettes) from which leaves can be produced.
Ravetta (1994) found that photosynthetic rates in H. funifera were highest during the fall months. High fall photosynthetic rates are consistent with the high daily growth rates that are observed in the fall (Fig. 1). Solar angles and night temperatures are lower in the fall than in the summer months and this may promote the higher photosynthetic rates. There may also be enhanced sink capacity in the fall when the lateral rosettes which emerged during the summer are growing at a rapid rate.
The agronomic significance of CAM is high WUE, and our initial biomass production trials confirmed that the high physiological WUE of Hesperaloe funifera did indeed translate into low water requirements (McLaughlin 1995; Table 3). Water-use efficiency was very low during the first year of stand establishment from transplants and very high during the fifth year (0.29 to 0.44 t DW cm-1). For comparison with the WUE values shown in Table 3, alfalfa grown in Arizona has a WUE of about 0.09 t DW cm-1. Averaged over 5 years, including year 1 when the crop uses all resources inefficiently, WUE in H. funifera is about twice that of C3 crops. Regrowing stands are expected to have a higher WUE than newly established stands.
This proposal was reviewed favorably by the AARC Center. However, during subsequent negotiations, JRC decided not to commit to a new major business venture at that time. The primary reason was the price of pulp, which hit an industry-wide low in the 4th quarter of 1993 (Fig. 5); major pulp manufacturers were not making a profit with softwood kraft pulp selling for less than $500/t.
Based on preliminary statements of interest from several paper makers specializing in higher-value products, the AARC Center agreed to fund the University of Arizona for a one-year period (Jan.-Dec. 1994) to develop a consortium of private-sector parties to take over the commercialization of Hesperaloe. The AARC Center stipulated that this consortium should consist of no fewer than five companies in the pulp and paper industry. A consortium was successfully organized with Arbokem, Inc., a specialty pulp manufacturer, as the lead organization. Six paper makers initially agreed to participate in the consortium.
The consortium submitted a second proposal to the AARC Center in August 1994, but this proposal was not accepted. The new AARC Center Board of Directors, under pressure for early commercial successes, felt that commercialization of Hesperaloe was too much of a long-term project (B. Crain pers. commun.). Following the AARC Center's rejection of this proposal, several of the paper makers involved decided to terminate their participation in the consortium.
We are currently working with a single pulp manufacturer (Arbokem, Inc.), and a single paper maker; the latter company prefers not to disclose its participation at this time. Under the direction of Wayne Coates of the University of Arizona, enough Hesperaloe funifera biomass will be harvested to ship approximately 2-3 t of decorticated fibers to Arbokem for pilot-scale pulping trials. The pulp will then be used for pilot-scale paper-making trials. If the results of these pilot-scale trials are satisfactory, a decision to move forward with a commercialization program could be made.
The major limitation on commercialization at this time is seed supply. We have been harvesting and cleaning seed from our experimental plots and have accumulated enough seed to plant about 150 ha. The first plantings of Hesperaloe funifera on demonstration farms will have to accomplish several objectives, including further development and testing of best management practices, seed production, and biomass production. Commercial-scale fiber production, approximately 20,000 to 25,000 t bone-dry pulp per year, would require about 5000 ha of cropland. However, assuming that the production cycle for Hesperaloe entails harvests at ages 5, 8, and 10, it is difficult to devise a planting scenario that would produce the exact quantity of biomass required each year by the pulper. One potential scenario is shown in Fig. 6, which assumes a yields of 180 t FW ha-1; an initial harvest at 5 years, and a productive lifetime for the stand of just 10 years. Under this plan, full production for a single processing plant would be reached at year 8. There would be excess production in years 13, 15, and 20, and sufficient biomass production to double the pulping capacity in year 26. Many different commercialization plans could be devised, but they would all have to share 2 basic features: an initial period of demonstration-scale production (ca. 50-200 ha) for increased seed production, followed by staggered plantings at full commercial scale. Sizes of plantings, planting dates, harvest dates, and the number of years that plantings remain in production could all be varied to adjust the annual supply of raw materials.
We established expanded plantings of Hesperaloe funifera at the University of Arizona Maricopa Agricultural Center this past year. We have encountered many problems, including production of vigorous transplants, adequate preparation of beds, effective transplanting with available equipment, and weed control. The slow growth rate of Hesperaloe during its first year following transplanting (Fig. 1, 2) make this crop a very poor competitor with weeds. All weed control during stand establishment will have to be accomplished using cultivation and chemical control. William McCloskey and Ramon Cinco-Castro have conducted preliminary work on herbicide evaluations. All pre-emergent herbicides tested proved to be phytotoxic to Hesperaloe funifera, but the plant did appear to tolerate several post-emergent herbicides.
Over the near term, lack of adequate supplies of seed and the long period of stand establishment (5 years to first harvest) will limit how rapidly commercialization of Hesperaloe can proceed. The private sector, like the AARC Center, may balk at investing in a project with a comparatively long payback period. Growers, processors, and paper makers will have to find a mutually acceptable way to share the risks and establishment costs.
Basic research on Hesperaloe, including continued studies on biomass production, agricultural engineering, water use, and weed control, is currently being supported by the USDA Cooperative State Research, Education, and Extension Services (CSREES). Lack of longer-term AARC Center support for commercialization is probably not a major obstacle to successful commercialization. Potential support from the AARC Center provided a good incentive for many private-sector parties at a time when market pulp prices were very low (Fig. 5). With an economically healthier pulp and paper industry, federal support for commercialization is less critical.
|Pulp type||US $/Mg|
|Well-cleaned, bleached fiber pulps (abaca, hemp, flax, sisal)||$1800-$2400|
|Not so-well cleaned, unbleached fiber pulps (hemp, flax, kenaf, cotton lint)||$1200-$1800|
|Special softwood pulps||$750-$850|
|Normal softwood pulps||$550-$750|
|Normal hardwood pulps||$450-$550|
|Fiber||Mean length (mm)||Mean width (µm)||L/W Ratio|
|Kenaf bast fiber||2.74||20||135:1|
|Water applied (cm)||Biomass production (Mg DW ha-1 y-1)||WUE (Mg DW cm-1)|
Fig. 1. Cumulative biomass production and daily growth rates in fresh weight measured over a 5-year period in a sample of 20 plants of Hesperaloe funifera.
Fig. 2. Biomass production of Hesperaloe funifera at three stand densities measured over a 7-year period. Plots were completely harvested at the end of 1992 after 5 years of growth.
|Fig. 3. Relationship between plant size and stand density in Hesperaloe funifera.|
Fig. 4. Potential crop cycle for Hesperaloe funifera.
Fig. 5. Prices of market pulps, 1989-1995; adapted from Presley (1995).
Fig. 6. An agricultural production plan for commercialization of Hesperaloe. Initial demonstration farm plantings will provide the seed for full commercial scale-up. A sequence of plantings will be required to provide a uniform supply of materials to a pulping facility. Each box represented a planting lasting 10 years and producing 18 t pulp ha-1 (from 180 t FW ha-1) at years 5, 8, and 10.