By Jane Moorman
Trees could serve as fuel source and as phytoremediators
On the wind-swept plateau south of Farmington, N.M., the idea of commercially grown trees might seem farfetched. While various forms of irrigation have allowed the Navajo Agriculture Product Industry (NAPI) to raise a wide variety of produce, grains and hays, the idea of raising trees takes agronomy in the area to a new level.
Mick O’Neill, superintendent and associate professor of plant and environmental sciences at New Mexico State University’s Agricultural Science Center in Farmington, envisions a viable new crop for NAPI that could impact the economy and environment – poplar trees.
For the past seven years, O’Neill and the science center staff have been working to answer the question of whether poplar trees can grow in the Four Corners’ semiarid temperate zone under drip-irrigated conditions. And if they can, which clone – a particular cross resulting in a hybrid – of poplar would do the best?
O’Neill felt the quest was doable because of success in the Pacific Northwest, where the climate of the Washington and Oregon area east of the Cascade Mountains is similar to the Four Corners area.
Both areas have about eight inches of annual precipitation, a 165-day frost-free growing season, and calcareous soils with elevated pH.
In the Central Columbia River Basin, GreenWood Resources is raising hybrid poplar trees on 25,000 continuous acres of drip irrigation. “We know it can work,” O’Neill said. “But can we do it here? That’s the question.”
Multiple economic opportunities
Originally O’Neill saw a need for trees as breaks along fields against the hard spring winds, but as he developed the study, viable economic opportunities have risen for the harvested wood.
“Our first thought was woody fuel, because 50 percent of the domestic energy source used by the Navajos on the reservation is from either fuel wood or coal,” he said. “So we were working on the concept of: Can we grow some fuel wood that can be used by the reservation?”
As word of the research got out to the surrounding area, economical use for the wood became apparent in two areas – wood fiber as excelsior for cooling pads or soil conservation blankets placed along road cuts, and as a biofuel to use as co-fire fuel for Four Corners power plants or in a cellulosic conversion process to make ethanol.
“Western Excelsior, an excelsior manufacturing company in Mancos, Colo., which is about 60 miles north of Farmington, heard about our research and we have been discussing if we could grow poplar as a substitute for the aspen they already harvest in the national forests,” O’Neill said.
“It would be more economical for them to harvest poplar on a flat surface instead of aspen on a mountain side, and it could be a long-term sustainable source of their raw material,” O’Neill said. “As we started our research we thought it would be a 10-year rotation from planting to harvest, but our work has demonstrated we are getting the 10-inch diameter tree they want in seven to eight years.”
During the first year of the study in 2002, the science center’s staff planted 10 different clones replicated three times.
“We saw right away that some of the clones did not like our environment, so we have followed eight clones over the course of six growing seasons. During that time one clone has grown to a diameter at breast height of eight and a half inches. Western Excelsior wants a 10-inch diameter log within a 10-year period. We are looking at something that can hopefully be used,” O’Neill said.
In a second trial, staff planted the trees at a high density spacing to mimic biofuel production.
Co-firing can reduce power plant pollution
“With two coal-fired electrical power plants in the Four Corners area, we raised the question, can we produce a product that could be combined with coal, a process called co-firing, and reduce the demand for coal by using a biofuel which is a renewable fuel source,” he said. “Research has demonstrated at other power plants that the mixing of wood with the coal significantly decreases the total carbon dioxide and particulate matter that is emitted from the plant stacks. Wood smoke is better than coal smoke with less carbon dioxide and particulate matter in the air.”
To see a decrease in the pollutants, O’Neill said, only about 1 to 5 percent of the co-firing fuel needs to be wood. “If you have six million tons of coal being used, 1 to 2 percent is a significant amount of wood that would have to grow and chip. Plus it would have to be done in a rotation that would make it sustainable.”
For this purpose, the size and shape of trees is not an issue, he said. “We just need a lot of mass in the trunk and branches.”
The New Mexico Legislature has established requirements that by 2020, 20 percent of the electrical generation must come from a renewable source, but it did not include co-firing in the regulations.
“Despite the fact that at this time it is not included in the law, we think there is still an interest in co-firing,” O’Neill said. “Some PNM people are showing interest in it and they think we should continue our work. And we have talked with several legislators and they think it could be included in a revision of the law. While there is still some political work to do, once we show there could be a source for co-fired fuels in close proximity, we think it would be a viable renewable source for these power plants.”
On another front, the Agricultural Science Center in Farmington will be working with Washington State University, GreenWood Resources and a chemical company out of British Columbia, Canada, to develop wood with characteristics that enhance the cellulosic conversion process to produce ethanol.
“The chemical company has a patent on a particular cellulosic conversion process that is more efficient than what is being worked on right now,” O’Neill said. “We will be working with Washington State University and Greenwood Resources to produce the wood products for that process.”
A third use for poplar trees is as a phytoremediator.
“Poplar tree roots absorb nitrates in the ground water. Because of this they can be used in phytoremediation of old uranium processing sites where high nitrate concentrations have contaminated the ground water,” O’Neill said of a project NMSU is doing in collaboration with Stoller Corp. of Grand Junction, Colo. “Stoller has the contract with the U.S. Department of Energy to clean up old uranium sites across the United States.”
Meanwhile, NAPI is beginning to tool up to raise poplar trees.
“NAPI is showing interest in poplar trees as a crop,” O’Neill said. “It’s a whole different cropping, management process and attitude about crop production. They will be going into a crop that takes seven to 10 years before it generates revenue. Plus before planting the trees there are significant start up costs in installing the drip irrigation system.”
NAPI planted 100 acres of poplar trees in 2004 and another hundred acres in 2007.
“They are interested, but they have to do some economic evaluation to see how their bottom line is affected and how they will afford the up front costs. Ideally, the startup and production costs will be recouped with the harvest income,” O’Neill said as he envisions the impact poplar trees could have on the Four Corners’ economy and environment.