BOONE, Iowa — Dick Thompson stands on the edge of the concrete manure pit he built in his field, a high point here in the middle of Iowa, and gestures toward the piles.

Against the far wall is a contribution from the nearby town of Boone — human bio solids that Thompson uses as fertilizer along with the manure he collects from his own hogs and cattle, some still steaming in the cold winter air.

"What comes from the land," he said with a glint in his eye, "should be returned to the land."

Thompson, 81, doesn't farm like his neighbors. But his 300 acres have become a destination for farmers and scientists from around the world who come to witness something exceedingly rare in the Midwest — a diversified farm.

By working with nature rather than against it, Thompson has carved out a middle ground between organic purism and the chemically intensive agriculture that is the norm in the Midwest. In so doing, agronomists said, he is modeling a kind of sustainable farming that could show a way forward against the loss of the prairie, global food demand and agriculture's impact on land and water.

Agricultural researchers have put a decade's worth of numbers to Thompson's style of farming. They found it's just as profitable and productive, if not more so, than relying on chemicals and genetic technology. Over time, it's 200 times less toxic to water.

"It's a pragmatic middle approach," said Jonathan Foley, who heads the University of Minnesota's Institute on the Environment.

There was a time, Thompson said, when he farmed like everyone else. He bought fertilizer and pesticides by the bag, and planted corn every year. But in the late 1960s, he went to a meeting where a speaker predicted those chemicals would turn out to be a blind alley for farmers.

That's when he realized, he said, "The answer is not in a bag."

Today, a satellite view of the Upper Midwest would show a checkerboard landscape in basically just two colors — corn and soybeans. It reflects a transformation driven by genetic and chemical technologies that do come in a bag, as well as federal crop subsidies and mandates for ethanol.

"In that artificial system, farmers would be crazy not to grow more corn," Foley said. "That's how we make more money."

It also is driving a massive conversion of the nation's few remaining grasslands into chemical-intensive row crops. Since 2008, some 37,000 square miles of grasslands, wetlands and shrublands have been converted to agriculture, according the Environmental Working Group in Washington, D.C.

Now, however, there are signs the strategy may have reached that blind alley Thompson was warned of years ago.

Weeds and insects have evolved to become resistant to the latest poisons, forcing farmers to use even more chemicals on the land. And despite increasing conservation efforts on the part of farmers, water throughout the Midwest is contaminated with agricultural fertilizers, pesticides and soil.

Forty years ago, just as the revolution in agriculture was about to take off, Thompson went in the other direction. He started farming much the way his father had on the same 300 acres. Instead of just two crops, corn and soybeans, he has honed a strategy that includes annual rotations of four crops in five years — corn, soybeans, hay and oats.

Crop rotation prevents insects from gaining a foothold in his fields; alfalfa and soybeans help restore the soil's natural chemistry.

And he makes a profit: An average of $218 per acre since 2000 — without federal subsidies — compared with an average loss of $10 per acre in Boone County, by his calculations. The difference is the money he doesn't spend on fertilizers and pesticides.

Of course, it's taken him years to figure it out. He's bought specialized equipment from Europe. It also requires a lot more time and daily management, plus livestock to eat the oats and alfalfa, for which there isn't much of a market anymore.

Which makes some question how many farmers would adopt Thompson's methods.

"That's the way my dad farmed in the 1950s and '60s," said Robert Plathe, a corn and soybean farmer west of Mason City.

But, he pointed out, it's a lot harder, and few people want to farm like that anymore. Animals require daily care, both in the winter and summer.

Mixed farming does require more work — a third more in labor costs, according to a study published in October that compared diverse farming with conventional. But the payoff in other respects was substantial, said Matt Liebman, an Iowa State University agronomist who led the research. Planting four different crops during four years resulted in a 92 percent reduction in fertilizer and a 97 percent reduction in herbicides, Liebman found.

And during the last six years of the study, the reduction in herbicides resulted in a 200-fold decline in water toxicity.

Between 2003-11, revenues on the experimental farm were lower for the diverse cropping system because crops like alfalfa and oats pay less than corn and soybeans. But, overall, profitability was about equal, Liebman said.

"Very small quantities of chemicals, when combined with ecological processes, can have powerful effects," he said.

Reach Josephine Marcotty at Josephine.marcotty@startribune.com.