Ongoing biofuel field trials are yielding positive findings which one day could give California and Arizona farmers a new option to diversify their crop portfolios while producing renewable energy.
Switchgrass, miscanthus, jatropha, sugar crops, and alfalfa are among the commodities under the field microscopes of Western researchers. Several crops were discussed at the 2010 Alfalfa, Forages, and Biofuels Field Day at the UC Desert Research and Extension Center (DREC) in El Centro, Calif.
Switchgrass has good yield potential for irrigated regions of California, according to Dan Putnam, University of California (UC) Cooperative Extension forage specialist, Davis, Calif.
“Whether switchgrass fits in will depend on a lot of factors. We don’t have the all the answers yet,” Putnam said.
Switchgrass, Panicum virgatum L., is a productive and widely adapted crop sown by seed. The hardy, perennial rhizomatous grass begins its annual growth in the spring. The grass can grow 4-7 feet tall. Leaves measure 30-90 centimeters in length with a prominent midrib.
Switchgrass uses C4 carbon fixation which means it is fairly efficient in the photosynthesis process and tolerates drought and high temperatures, Putnam says. The grass has low fertilizer requirements and grows well on marginal land.
The U.S. Department of Energy calls switchgrass an important candidate as a whole plant cellulosic ethanol biofuel.
UC is working with Ceres, Inc., Thousand Oaks, Calif., on four California switchgrass variety evaluation trials. The sites are located at the UC’s Westside Research and Extension Center (WREC) in Five Points, DREC, the Plant Sciences Research Farm in Davis, and the Intermountain Research and Extension Center in Tulelake.
Ten experimental lines were planted at the trial sites in 2007. Putnam noted the following year-by-year switchgrass findings.
• First year results: Some variety lines performed well at all trial locations. Yields were “reasonable,” higher in cooler-growing areas.
• Second year: Some varieties provided “reasonably high” yields including 18 tons/acre in Five Points and El Centro. Switchgrass was harvested once in Tulelake; some varieties died due to the colder climate.
The Davis trial was cut twice with yields in the 6-9 tons/acre range.
• Third year: Several varieties exceeded 14 tons/acre in Five Points and 13 tons/acre in El Centro. The Davis trial was cut twice with 11-14 tons/acre yields. A single harvest in Tulelake yielded 8 tons/acre yields; frost killed several varieties.
Plant growth was slower this spring at each trial location, Putnam says, tied to cooler and wetter weather.
Jatropha, Jatropha curcas L., is a perennial plant under study for its high oil content for use as biodiesel. The plant’s inedible seeds contain 35 percent to 45 percent oil.
“Jatropha is a water frugal, hardy, and heat-tolerant plant,” said Sham Goyal, plant agronomist and professor emeritus from UC Davis.
Goyal is part of a five-member team studying jatropha as a potential biofuel crop in the Golden State.
“I have never found a plant that is more drought tolerant than jatropha,” Goyal said. “This very characteristic makes this plant very suitable for the Imperial Valley. This plant can get by on a minimum amount of water.”
Goyal is a native of India where jatropha has been grown for hundreds of years as a “live” fence. Animals do not eat the branches, leaves, or fruit. The Indians only recently discovered jatropha’s high oil content.
“Jatropha is a wild plant; there has never been any varietal improvement.”
Goyal brought seeds from India for planting into jiffy pots at a UC Davis greenhouse. The seedlings were transplanted into two-acre field trials at the DREC, the South Coast REC in Irvine, the Shafter REC near Bakersfield, and UC Davis in 2008. The three-year trials are sponsored by Chevron.
Jatropha grows up to 12 feet tall and achieves full fruit production in about five years, says Goyal. The plant produces fruit for about 40 years. A mature plant yields 1-3 kilograms of seed. About 1,000 trees are planted per acre in the trials. November and December is the harvest window.
“We need several more years to determine the actual yields,” Goyal said.
Some estimates peg the plant’s biofuel yields at 300-1,000 gallons of diesel per acre per year. The 600-gallon range, says Goyal, is a more reasonable estimate.
“This is a tropical plant which does not like the cold weather,” Goyal said. “If an area drops below 30 F, I would not consider it. We also don’t know how jatropha will handle extreme heat in the 115-118 degree range.”
Goyal is uncertain whether jatropha is a salt-tolerant plant.
“We estimate about 2 acre-feet of water is needed to grow a maximum crop,” Goyal told the farm crowd. “Drip irrigation would likely reduce the water requirement.”
Purchasing jatropha seed from outside of California requires an import certificate. Goyal has not found any serious diseases or pests in the jatropha trials. Whiteflies are found around the plants in the summer with no damage reported.
Team members Uriel Rosa and Shrini Upadhyaya, UC Davis engineers, built a prototype jatropha mechanical harvester and field tested the machine last year in a mature jatropha field in Hawaii. The harvester worked well overall; several equipment modifications are planned.
Other team members, all with UC Davis, include plant scientist Anna Davidson, plant geneticist Dan Parfitt, and engineer Bryan Jenkins.
Miscanthus is a tall perennial C4 grass currently grown as an ornamental and recently proposed as a biomass crop.
According to a handout from Dan Putnam, the most common biofuel variety is the sterile hybrid Miscanthus x giganteus which originated in Japan. Seed companies are studying Miscanthes sinensis varieties grown from seed for biofuel production.
Miscanthus reportedly produces high yields sufficient for the production of heat and electrical power, or for conversion to other energy products including ethanol.
The potential crop advantages include high yields, low agronomic inputs, low mineral content, wide adaptation, and frost tolerance.
Miscanthus, corn and switchgrass reportedly have similar ethanol conversion yields. One harvest per year is common.
Current Miscanthus x giganteus types must be planted via clonal rhizomes which are collected and spread mechanically. This is a limitation, Putnam says. Research on seed-producing lines is underway which could lower stand establishment costs.
Several miscanthus varieties were transplanted into a 1.5-acre plot at UC Davis in 2008.
“When we first planted the miscanthus I was not very optimistic,” Putnam said. “In the second year the miscanthus really took off. Some new varieties planted for the third year were chest high. It will be interesting to determine how miscanthus performs over time.”
Mike Ottman, University of Arizona (UA) Cooperative Extension agronomist, discussed forage sorghum as a biofuel crop for cellulosic ethanol.
“Forage sorghum as silage requires about 150 pounds of nitrogen in desert production; about half of the N requirement for silage corn,” Ottman said. “N is one of the top energy inputs required in forage sorghum production.”
Forage sorghum is a short-season crop planted in July and harvested in October in the desert. The crop grows to 6-10 feet tall.
Ottman estimates cellulosic ethanol yields at about 24 gallons per wet ton of forage sorghum; or about 550 gallons per acre for a 23-ton per acre crop.
Ottman’s current forage sorghum trial at the UA’s Maricopa Agricultural Center in Maricopa, Ariz., is funded by the United Sorghum Checkoff Program.
As interest continues to mount regarding biofuel crops, Putnam suggests growers keep an open mind on cropping options and continue to ask questions.
“There may be a combination of crops – sorghums, sugarcane, and sugar beets, for example – as potential energy crops,” Putnam said. “Even alfalfa could be an interesting energy crop if we looked at splitting the leaves and stems into two components.”
Putnam calls alfalfa a biofuel crop contender due to its ability to fix its own nitrogen supply.
“We have to open our minds and try to understand where these energy crops might fit or be rejected over time,” Putnam said. “We need to introduce these crops, experiment with them, determine the yields and problems, and then make recommendations over time.”