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.

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

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.

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.

Are methods under consideration by researchers.

"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."

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.

A surface blanket, and a horizontal pipe injection system

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.

"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."