CARIBOU, Maine — Maine farmers who want to grow industrial hemp like their counterparts in Canada and Europe should start writing letters to their representatives in Congress, John Jemison suggests.

Jemison, an agricultural specialist at the University of Maine Cooperative Extension, is among several researchers in New England investigating hemp as a crop that could be grown for everything from fishing ropes to insulation and seeds rich in nutrients and protein.

“It has the potential to be a really good rotation crop,” Jemison told farmers at the Maine Potato Conference held earlier this month at the Caribou Inn and Convention Center.

The trouble is, even though Americans can buy hemp jeans or hemp granola, the plant can’t legally be grown for commercial use in the U.S. and instead must be imported. As part of the prohibition on marijuana, the varieties of cannabis used as a recreational drug and medicine in some states, federal law still prevents cultivation of hemp. Hemp looks similar to marijuana but has different genetic and physical traits: thicker stalks, smaller flowers and virtually no tetrahydrocannabinol or THC, which is responsible for the high that marijuana users feel.

At least 27 states have passed legislation related to hemp, in an effort to allow commercial production, research or cultivation that would be contingent upon federal reform, according to the National Conference of State Legislatures. The 2014 U.S. Farm Bill allowed hemp cultivation for research purposes, with a Drug Enforcement Agency permit, and small plots were planted last year in Kentucky by farmers working in partnership with the state government.

A 2015 Maine law permitted a system for commercial cultivation, despite the federal prohibition, and the Department of Agriculture, Conservation and Forestry has released proposed regulations that outline a system for licensing, seed procurement and limitations on the quantity of THC, to less than 0.3 percent.

However, the proposed rules come with a disclaimer: “Persons growing industrial hemp may be subject to federal sanctions for what may otherwise be considered authorized conduct in the State of Maine and compliance with these rules does not exempt licensees from possible federal prosecution.”

A Maine hemp license would cost $500 and $50 per acre under the state Department of Agriculture’s proposed rules. That still carries the risk of liability for violating federal law, without getting a DEA research license, which Jemison would like to get if he can secure funding for research.

Hemp and marijuana are varieties of the cannabis plant, which has “been domesticated about as long as we’ve had agriculture,” Jemison said. The plant is thought to have first been used medicinally in China “for pain relief, neuralgia and, interestingly enough, absent-mindedness. I’m not sure if they were trying to reduce that or increase that,” he joked.

Cannabis as hemp was grown in the United States as early as the 1600s to make everything from ship sails to paper, and then in the 1800s, newfound varieties of cannabis were used in various concoctions sold as a medicine, Jemison said.

Hemp and marijuana appear similar as they grow, with the characteristic slender leaves, but they have been bred for different things — marijuana for its seedless flowers full of THC and other compounds and hemp for its thick stalks and hearty seeds. (For those interested in cannabis’ natural history, Jemison recommended Michael Pollan’s book “The Botany of Desire,” which details how agronomists bred shorter, high-THC marijuana varieties to help illegal growers over the last 50 years.)

The hemp plant has a trifecta of product lines in fiber, “shivs” and seed, according to Michael Carus, director at the European Industrial Hemp Association, based in Huerth, Germany. Hemp fibers are used for papers, insulation and biocomposite materials, while the shivs, the silica-rich woody core of the stem, can be used for animal bedding and construction infill as “hempcrete.” The nutty hemp seeds have a balance of omega-3 and omega-6 fatty acids and a range of beneficial nutrients for people and animals.

Canadian farmers have been growing hemp mostly for food products for more than a decade, after their prohibition was lifted in 1998. More than 84,000 acres are licensed from Health Canada for hemp cultivation across the provinces, and retail sales of Canadian hemp seed products range between $20 million and $40 million annually, according to the Canadian Hemp Trade Alliance. Europe’s niche hemp industry relies on about 25,000 acres in production focused on fiber uses, including BMW hemp reinforced door panel and building insulation.

For Maine potato farmers, who have a range of rotational crops to choose from, hemp would pose benefits as well as drawbacks, Jemison said. It doesn’t require too much fertilizer or pest management, though it does use a lot of carbon from the soil and is rough on the machines that harvest them.

“That being said, if you have marginal land and you wanted to do some of this, there may be a place for that,” Jemison said.

Research in Quebec, which has a growing season similar to Aroostook County, has shown strong hemp yields, if less than those in western Canada. “It’s a decent crop,” Jemison said.

The markets for fiber are small, but hemp seed and hemp seed oil would be similar to growing other seed oils and with a premium price, Jemison said. “Back of the envelope,” he estimates Maine farmers could grow 35 to 50 gallons of hemp seed oil per acre, compared to 75 to 100 gallons of canola oil per acre, with hemp oil selling for about 20 times as much per ounce.

The Maine Department of Agriculture, Conservation and Forestry is holding a public hearing on its proposed rules Feb. 25 in Augusta and accepting comments through March 7.

Jemison is meeting a Vermont researcher who has secured a DEA license and will be at the February hearing. He said he thinks Maine’s hemp regulation could work like the state’s medical marijuana licensing program, but that it’s really going to take an act of Congress to allow the crop and new industries to grow.

For Congress to pass a law allowing hemp cultivation, which among other things could mean a new competitor to the cotton industry, lawmakers need to hear from their constituents, he said. “If you all push on it, I think we could get some progress on the national level,” Jemison said.