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Jim Chapman, executive director of the Potato Growers of Idaho in Blackfoot, says farmers can overdo a good thing.

Chapman is a "firm believer in good, long rotations," and he would like to see potato growers planting spuds less frequently in the same field."We've given up good, long-range farming practices for short-term gains, simply because the economics have forced us into that," he says.

Paul Patterson, University of Idaho Extension agricultural economist in Idaho Falls, acknowledges that shorter potato rotations have some short-term economic advantages for growers.

"But the longer-term implications are negative, and they are starting to show up in changing soil characteristics, which are having some impacts on the quality of the potatoes that the growers are producing," he says.

Chapman says agricultural profit margins are typically "so thin that growers are farming to generate revenues to pay the bills this year and will worry about next year next year."

But that's shortsighted, he says. "Those who practice good, long rotations will net more dollars in 10 years than those who do not."

The figures support Chapman's observations that short rotations are the norm. A 1992 University of Idaho survey found that one third of eastern Idaho commercial potato growers planted potatoes in the same field every other year. Nearly half planted them in the same field every three years. And only one in six used rotations of four years or longer.

"There are growers who have every-other-year rotations and they do grow high-quality crops," says John Ojala, University of Idaho Extension potato specialist in Idaho Falls. "But that's not what we're advocating. It just increases their production and management problems in the long term."

Because diseases, weeds, insects and nematodes that plague potatoes increase whenever spuds are in the ground, Ojala says it's invariably "much more challenging to produce a quality crop of potatoes with closer rotations. And the question arises, is that a sustainable practice? What happens in 30 years?"

Ojala's counterpart in southwestern Idaho, Mike Thornton, puts the most common potato rotation in his area at four years or more.

Not only does the Treasure Valley's longer growing season give farmers more choices of crops to rotate with, Thornton says, but it forces them to stay out of potatoes longer.

That's because southwestern Idaho's typically longer summers and warmer winters contribute to even faster buildups of potato pests - making the potential penalties for shorter rotations even more severe.

Steve Trevino, sales manager at Rolland Jones Potatoes Inc. in Rupert and chairman of the Idaho Grower Shippers Association, says he would like to see rotations of six to seven years. But he concedes that "very, very few growers are able to do that, especially in the eastern part of the state."

"They have grain and potatoes, and potatoes have really been the only thing that has made any money over the last several years."

Brian Finnigan, University of Idaho Extension agent in Bingham County, says annual alfalfa - as well as the annual canola some are already growing - deserves consideration as a crop eastern Idaho farmers might include in longer potato rotations.

"You can see where a potato grower wouldn't want to take a field out of production for three to four years to grow alfalfa," Fin-nigan says. "But if he could get a benefit in quality and quantity of potatoes following annual alfalfa - which there is already an established market for - he would be more likely to grow that crop than grain."

In Aberdeen, University of Idaho agronomist Jeff Stark and Dale Westerman, a soil scientist for the U.S. Department of Agriculture's Agricultural Research Service, have found that a previous single-year crop of "Nitro" alfalfa can provide most of the nitrogen required by a subsequent potato crop and still provide economic returns to the grower.

Patterson emphasizes that the alfalfa market is demanding more high-quality dairy hay. Growers of less than top-quality hay "may find a market, but it's not going to be a market that will allow them to sell that crop at a profit."