Gaining Steam

July 1, 2008 By    

If estimates hold true, the propane industry is poised for massive, off-peak market growth in the agricultural sector that could add 10 million gallons in annual sales.

Propane-powered steam heat is being used in extensive laboratory and field testing to control soil nematodes. These microscopic worm-like parasites can affect crop yield and quality by invading plant roots or surrounding soil and stealing nutrients.

For decades farmers have used methyl bromide, a chemical fumigant, to control these pests. Because of health and environmental concerns, however, it was to be phased out for most crops by 2007. Critical-use exemptions still allow the chemical if there are no alternatives.

 Nematodes are microscopic parasites that feed on other organisms and inhabit agricultural soil.
Nematodes are microscopic parasites that feed on other organisms and inhabit agricultural soil.

One particular project in progress aims to provide that chemical-free, low-cost alternative to methyl bromide and replacement chemicals. The Propane Education & Research Council (PERC) is funding the project and contracting with Gas Technology Institute (GTI) for the research.

Neil Leslie, a research and development manager for GTI, says there are two elements to the project. The first is solving the growers’ problem of controlling soil nematodes; the other is providing an economically viable replacement to methyl bromide and other chemicals.

“We wanted to understand what alternative methods are out there and identify anything that might qualify as a heat-based alternative as opposed to chemical bases,” Leslie says. “We also wanted to understand the heat transfer process.”

Are methods under consideration by researchers.
Are methods under consideration by researchers.

Two-phased approach

The project is being funded in two phases, the first of which was recently completed. It focused on determining the most efficient way to transfer heat.

“One thing everyone agrees upon is that heat will control these pests,” says Mark Leitman, director of agriculture programs for PERC. “The elusive challenge is how to effectively get that heat into the soil. Propane is well positioned to provide the energy for that heat. In the first phase of this effort, we looked at all sorts of ways to get propane-generated heat into the soil.”

After a series of laboratory and field tests, aerated steam was chosen as the preferred method because it condenses quickly to heat the surrounding soil. While researchers prefer steam as the best way to transfer heat, they still are evaluating the best mechanism for getting it into the soil. That question should be answered in the second phase, when propane-fueled systems are developed and field-tested.

Three major methods of getting steam into the soil have been considered. They include a surface blanket with steam-filled pipes, a lance-injection system where steam comes from pipes spiked into the ground or an underground horizontal plastic piping system (also called drain steaming) where steam is released through perforations in the pipe.

A surface blanket, and a horizontal pipe injection system
A surface blanket, and a horizontal pipe injection system

“As we did the lab work, we were getting a chimneying effect with the lance system,” Leslie says. “Steam would come around and not go sideways very far, so we were not able to get the bulk soil heated the way we wanted. So we focused on pipes under the soil as our Phase 2 work.”

Partner emerges

While GTI was conducting its research and selecting to test its underground piping system, Steve Fennimore, an associate extension specialist with the University of California-Davis, was receiving $425,000 in funding from the U.S. Department of Agriculture (USDA) for a similar project. Focusing on propane-powered heat to control weeds, Fennimore has used steam blankets and a steam hose on a lance-injection system. He has agreed to coordinate his work closely with the PERC project.

Major plant-parasitic nematode genera  in the U.S. and associated damage to plants
Major plant-parasitic nematode genera in the U.S. and associated damage to plants

“It’s refreshing to see a project partner emerge like UC Davis who is well known in the agricultural industry,” Leitman says. “They were interested to find out that we were embarking on our mission when we found them. We’re going to move forward together and share information.”

Fennimore prefers the lance-injection system in which pipes, or spikes, are hooked to a hose and placed 8 to 10 inches into the soil. He also didn’t get the same chimneying effect during his research as Leslie did. But Fennimore is keeping an open mind, choosing to see if Leslie’s underground piping method works.

“The hose system that we’re developing is a more practical system for us, but healthy skepticism is good for a project,” Fennimore says. “You challenge each other and make things better. We’re trying to come up with the best possible solution.”

Leslie is also keeping an open mind. While his lab tests showed buried piping performed the best in heating targeted areas of the soil, he’s willing to move his research in another direction.

“We’re trying to come up with the most cost-effective approaches,” Leslie says. “We have no problem shifting resources if [Fennimore’s method] turns out to be a technologically superior and economically smarter way to do it.”

The timing of their studies also aligns nicely. Fennimore is expected to begin his field work in August or September, coinciding with GTI’s implementation of its horizontal pipe injection system. Researchers hope to determine the most suitable technique for growers to use, considering factors such as land size, soil depth, soil temperature and time of treatment.

“It turns out this will go beyond nematodes,” Leslie says. “You can use steam to kill soil-borne pests and you can use steam to kill weeds. There are multiple benefits that the growers will find particularly useful.”

Leitman adds, “Because of the collaboration with UC Davis and the federal grant, we’re able to do more testing on more target pests and explore more methods of applying heat to the soil than we could do on our own.”

In addition to the USDA grant, PERC is providing $145,200 to help grow the partnership with UC Davis, funding propane equipment for testing and evaluation. PERC also allocated $342,000 in 2006 for the first phase of the project and $434,503 more in 2007 for the second phase.

Much of the research will be conducted in California and Florida, which are also target markets – areas with warmer climates and long growing seasons that can produce a variety of crops. Tomatoes and strawberries are major market segments; California has about 40,000 acres of fresh tomatoes and 35,000 acres of strawberries, while Florida cultivates about 50,000 acres between the two crops. In addition, 90 percent of this acreage has historically been treated with methyl bromide.

Organic crops also are growing rapidly in market potential for this type of project, since chemicals cannot be used to protect them from harmful pests. Fresh cut flowers are another potential market.

“If we do real modest penetration, we’re estimating to burn 10 million gallons of propane per year,” Leslie says. “If propane can become a major treatment of choice, the market opportunity is much larger.”

Moving forward

In the second phase, GTI will use a novel heat distribution system, which it designed at its offices in the Midwest, focusing on subsoil steam-air injection. In earlier testing, this horizontal-piping technique heated the soil to 130 degrees Fahrenheit to a soil depth of 10 inches. In this second phase, a 160-degree Fahrenheit steam will be used to control nematodes, weeds and other pests.

This prototype allows a polyethylene pipe containing holes to be placed 8 to 10 inches underground (pipe and hole sizes will be determined during research). A 25-horsepower boiler, fueled by propane, and a high-pressure fan will create the aerated steam. Leslie estimates that for each acre receiving treatment in the field, 500 gallons of propane will be burned to drive the boiler.

“I think propane is a great idea, and I’m all for it,” Fennimore says. “Air quality is a huge issue in California. CARB [California Air Resources Board] is encouraging people to switch to propane wherever possible. The price is a little cheaper and less volatile than diesel.”

GTI will use this prototype for its field tests to determine crop compatibility and efficacy on nematodes, weeds and other pathogens. Those involved in the project hope to develop a high-level commercialization plan in 2009, based on which methods are most successful.

“What takes time is the efficacy and the impact on yields,” Leslie says. “It takes one to two years to see if there’s a persistent value, to see which of these alternative approaches perform better and to look at the economic approaches. Then we can fine-tune things and determine what happens with the other complicated parameters, like the type of soil, the temperature in the region or project designs.”

PERC’s collaboration with GTI will last about two more years, Leitman says, while the UC Davis project will continue through the 2010 growing season. And with some crops still having critical-use-exemption status, opportunities exist for improved methods to invade the market.

“We’ll learn a lot in the next year or two about how far this can go,” Leitman says. “Hopefully we’ll have a blueprint for a propane solution that can control these pests.”

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