In Asia, the Chinese tallow tree has a reputation as a highly productive commercial tree. China has 1,500 years experience in using the five cultivated species of tallow tree for multiple uses. The outer coating of the seed provides a vegetable wax and the leaves produce a silk dye. The kernel oil, called stillingia, has drying properties that make it useful in paints. The oil is used for soap and lamp oil. The Chinese continue to develop products from the tree, says Gary Breitenbeck, a professor at the School of Plant, Environmental and Soil Sciences in the Louisiana State University AgCenter. Along with identifying pharmaceuticals, the Chinese developed a process to separate the oils and used the palmitic and oleic acids from the tallow to create a transfat-free shortening. Breitenbeck is hoping to attract a Chinese graduate student to LSU to help him translate Chinese research on the tree, and to evaluate and improve the tree. Breitenbeck says that while the Chinese have demonstrated the value-added potential of the tallow tree, he is the first to concentrate on developing it as a biodiesel feedstock. He sees great potential for the tree, but fears that two issues might sink it before he can tap into the possibilities. One is its invasiveness and the other is the potential for its premature commercial development that could result in low-yielding, unproductive plantings.
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Invasive Concerns
The invasive potential of the Chinese tallow tree is a serious concern that’s been raised in the development of bioenergy feedstocks when the attributes that make the plant an ideal bioenergy crop are shared by plants that become invasive. The Council for Agricultural Science and Technology recommends thorough risk evaluations prior to introducing new species, or even new cultivars of native species with traits that may pose problems. CAST, a nonprofit organization of 38 scientific societies and individual members including students, companies and other nonprofits, publishes science-based material for legislators, regulators, policy makers, the media and the private and public sectors. CAST also calls for the establishment of eradication protocols prior to introduction. Invasiveness concerns are also being addressed at the federal level. One example is USDA’s Biomass Crop
Assistance Program created in the last Farm Bill, which prohibits invasive species from being supported in the program.
Breitenbeck agrees that introducing Chinese tallow into new regions should be done with great care, but in Louisiana and along the coast into Texas, the tree is already a pest, he says. “The first land I want to convert is land already in tallow trees,” he says. ”I figure we have 100,000 acres in Louisiana alone.” Furthermore, cultivating the tree and harvesting the seeds may actually decrease its spread, he says. Breitenbeck says the Chinese tallow tree, commonly referred to as the chicken-foot tree, is reviled by many cattlemen in Louisiana but it doesn’t have to be that way. “If the tallow tree establishes itself and is not mowed in the first year, in the second year when you mow it sends out dozens of shoots,” he says. “It is easy to control under a reasonable pasture management system, mowing once a year or cultivating once a year.” LSU has chemical control trials underway now, using a wick applicator to apply contact herbicides to kill seedlings without killing the pasture grass underneath, he adds.
Commercialization Potential
Breitenbeck is excited about the prospect of developing the Chinese tallow trees into an income-producing crop for salt-affected and marginal lands. The coastal plains ecosystem is being impacted by rising sea levels and inundations from storm surges, he says. Hurricanes Rita and Ike carried seawater 50 miles inland, some of which drained within a few days, while some areas where the water was trapped were covered with saltwater for several weeks or even a year. There is hope that the land can be reclaimed to produce sugarcane and rice, he adds, but few crops and many tree species won’t grow on salt-affected lands. “I had some jatropha plantings south of New Orleans that didn’t survive,” Breitenbeck says. “Fortunately, the plant that will survive and contain erosion is the tallow tree.”
In addition to tolerating salt, the tallow tree grows well on marginal soil, tolerates prolonged flooding and occasional freezing temperatures, attracts few insect pests or troublesome diseases, and appears to be a low-input tree. “The tallow tree may be the ideal energy crop for biodiesel production along the Gulf Coast,” he says.
As a biodiesel feedstock, both the outer coating and the kernel of the tallow tree seeds are high in oil content, as the seeds contain 45 percent to 60 percent oil. Commercial plantations in other countries typically contain about 160 trees per acre, which are trimmed low for hand harvesting. Yields average 12,500 pounds of seed per acre, which can produce 2,300 pounds of stillingia oil, 2,500 pounds of vegetable tallow, 1,400 pounds of meal and nearly 5,000 pounds of biomass waste. In China, the meal is used as a high-nitrogen fertilizer. Breitenbeck says commercially produced trees average 645 gallons of oil per acre and some experts cite yields as high as 970 gallons per acre.
In the U.S., however, wild tallow trees and the ornamental trees grown by many homeowners have wildly variable seed yields and oil composition. Some trees have virtually no seed production, particularly those growing in shaded conditions, Breitenbeck says. “I’ve looked at thousands of trees and have selected 23, with a couple that are outstanding in every way,” he says. Work is progressing on growing the elite trees, and developing a micro propagation technique to aid research and commercialization. Research is needed to learn how much of the oil yield and composition depends upon genetics and how much depends on the environment.
Other research efforts are focused on developing agronomic management and machine harvesting. The uneven maturity of seeds and their waxy coating presents a challenge for mechanization. Researchers at LSU are experimenting with a harvesting method based on growing the trees in hedge-like rows. A boom-mounted sickle bar is used to prune the new growth branches containing the ripening fruit. The fruit on the young branches matures uniformly within a few days when it’s allowed to dry on the ground, and can be harvested using a combine modified to accommodate the wax-covered seed, which is slightly larger than soybean seed.
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