Farm equipment manufacturers are rolling out cleaner tractors to meet stricter new federal air regulations, but many in the industry say the challenge will be getting farmers to put the high-priced models into fields during hard economic times.

The rules that went into effect Saturday apply to tractors, construction vehicles and other so-called nonroad equipment. The U.S. Environmental Protection Agency says the vehicles are major sources of particulate-matter emissions — the stuff that makes smoke black and air difficult to breathe.

Federal air standards have been tightening since the mid-1990s. The 2011 regulations are the latest step, requiring that diesel engines built starting this year produce even fewer of the nitrous oxides that can cause acid rain.

Tractor makers, including Deere & Co. and Case IH, have unveiled a number of new models that meet the so-called Tier 4 standards. But with the greener technology adding about 10 percent to the price, many farmers say they're in no hurry to upgrade tractors that might last another 25 years or more. Others are upgrading but their old tractors are getting traded in and resold rather than retired.

Given that, the effects of the new regulations may not be felt for decades.

Paul Fortkamp, who raises poultry in Fort Recovery, Ohio, has upgraded, buying a Tier 4 tractor from Case IH in Racine, Wis., for use with his corn and soybean crops. The tractor treats the exhaust with a nitrogen-based compound that converts it to mostly water vapor and atmospheric nitrogen.

Fortkamp bought the $120,000 tractor to replace a 30-year-old vehicle that he plans to sell. He said his buying decision was based on cost, not environmental concerns.

"I needed to upgrade," Fortkamp said, "but the price of used equipment has gotten so high that I figured I might as well buy new. It wasn't a huge difference in cost."

The new tractors can cost $100,000 to $300,000. Manufacturers say they have added some new features to make the price more palatable.

A Tier 4 tractor made by Deere & Co., based in Moline, Ill., alerts the owner if a thief tries to drive it out of a specified area. To meet the new federal standards, the tractor has a system that captures and cools exhaust gas and then redirects it to the engine, where it can burn at a lower temperature and produce fewer emissions.

Case IH defended the price on its new tractor in part by noting its emissions system makes the engine 10 percent more fuel-efficient.

While environmental groups are usually vocal about supporting green technologies, the manufacturers seem to be the only ones pushing the new tractors.

The Sierra Club said the new machines and the rules that went into effect Saturday are just an incremental step following major air pollution legislation passed in the 1990s. And the Wisconsin Farm Bureau Federation said its members had more pressing issues to focus on.

Some farmers said they had no interest in the new tractors, even if they did promise to be more environmentally friendly.

Phillip Batho owns a dairy farm in Plum City in western Wisconsin, where he uses seven tractors to spread manure on fields and harvest crops. The new technology remains untested, he said, so he was skeptical about the government's and manufacturers' rosy claims.

That's why, when he needed a new tractor last month, he bought a used model for about $60,000.

"The newer ones, there's a lot more stuff to go wrong. They're a lot more complicated," he said. "I like having a clean environment as much as anyone, but the tractors we've been using don't seem to be ruining the environment."

He paused, then added, "I'm not looking forward to having a Tier 4."

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