PHOTO: Kermit Knutson, of Storm Lake, Iowa, right, shows Nuhn manure spreading equipment to Clarence Nagel, of Marathon, Iowa, during the Upper Midwest Manure Handling Expo. (AP Photo/Charlie Neibergall)

For the folks who make a living spreading manure on farm fields, the business end of hogs, cows and chickens can be a gold mine.

More than 1.3 million tons of manure is applied as fertilizer each year to about 15.8 million acres of farmland in the U.S., according to the U.S. Department of Agriculture. Much of it is handled by custom manure applicators who gathered in July in central Iowa to learn the latest techniques for handling the waste.

About 1,500 people, including custom manure applicators, farmers and others, attended the Upper Midwest Manure Handling Expo, an annual event held in Iowa for the first time.

They checked out spreaders, hoses and tanks parked in corn and soybean fields just east of Boone, watched demonstrations on handling solid and liquid manure, and attended classes held under white tents.

"We're in such an environmentally sensitive industry, it just keeps everybody up with the new technologies and handling manure in a safe and efficient manner," said Kevin Westaby, president of the Iowa Commercial Nutrient Applicators Association, which co-sponsored the event with Iowa State University.

It's also a chance for the industry to show the public how it has improved its technology and techniques to prevent runoff and other problems, Westaby said.

"We're not trying to pollute," he said, "and we're showing that it can be applied based on crop needs and in a safe manner to protect the waters of the state."

Large farms hire custom manure applicators to spread the waste on their land. Dean Wurzer, a custom applicator from near Hawkeye in northeast Iowa, said customer expectations have increased in recent years with tougher government oversight.

PHOTO: Craig Jorgensen, of Jackson, Minn., right, shows a Nuhn manure spreader to Gary Wilton, of Medora, Ill., during the Upper Midwest Manure Handling Expo. (AP Photo/Charlie Neibergall)

"The customers now expect a better job of manure hauling and you gotta keep up with the latest ways to do that," he said. "With tighter regulations and lower application rates, it's becoming much harder."

Manure is used as fertilizer on about 5 percent of U.S. cropland. Much of the rest is treated with chemical fertilizers. Corn, which is planted on about one-quarter of all U.S. farmland, covers more than half of the acres treated with manure.

AGCO, a farm equipment company from Minnesota, brought a prototype of a tractor and spreader that company officials said could cost up to $700,000, although a price hasn't been set.

The machine, called the TerraGator, gives the user better control over how much manure is released and where it goes, helping to reduce runoff into streams and lakes, said Arnie Sinclair, an official from the AGCO office in Waconia, Minn.

It's a big challenge to produce equipment that meets ever-stricter government regulations, Sinclair said.

"At the end of the day, we want to make sure everything is applied accurately," he said, adding, "It's hard to say manure is a science, but the reality is the handling of manure is a science."

Gary Wilton, a custom manure applicator from Medora, Ill., who does business in Illinois, Missouri, Texas, Oklahoma and The Netherlands said he talks to the Environmental Protection Agency or other regulators nearly every day to keep up to speed on the rules.

But he can get some guff from folks who don't understand how complicated his business is.

"It's hard for me to tell people what I'm doing," Wilton said. "You tell them I'm going to go look at a $600,000 machine, and they're like 'Just to spread hog manure?'"