They called him "Mr. Tillage" for his dogged pursuit of better soil management.

Raised on a Nebraska farm, Bill Larson was a career soil scientist who earned world renown for championing a more conservative mode of tilling farmland.

Larson's research showed that if farmers left residual pieces of harvested crops on the ground and merely loosened the soil, instead of plowing it under, the soil would be healthier, new plants would get more nutrients and erosion could be reduced by 50 percent.

"His research focused on the Midwest, but he had a national and international reputation," said John Baker, head of the U.S. Department of Agriculture's Agricultural Research Service in St. Paul and an adjunct professor at the University of Minnesota. "Students and researchers came from around the world to learn from him … from developed and undeveloped countries."

Larson worked as a federal researcher at Montana State University in the early 1950s and was on the faculty at Iowa State for 13 years. He spent 22 years at the University of Minnesota, first as a research leader and then as head of the Department of Soil Science.

Larson died on July 15 at the age of 91.

Though Larson retired from the U in 1989, he kept an office on the St. Paul campus. His mind remained sharp, Baker said, and he was often sought out for his historical perspective.

Mark Seeley, University of Minnesota meteorologist and climatologist, counted Larson as one of the university's most outstanding faculty members and department leaders.

"He was one of the most important and influential scientists and a widely admired and respected individual," he said.

While Larson's early work in the 1950s and '60s focused on the economics of land use and crop production, his career later evolved toward "a more environmental bent" in the 1970s and '80s, Seeley said.

Larson earned the field's highest award, the Siehl Prize for Excellence in Agriculture, in 1994 in large part because of his balanced approach to helping farmers get high yields while addressing environmental concerns, such as runoff and overfertilization. In 2001, Larson was inducted into the Science Hall of Fame from the USDA.

Larson and his colleagues did some early research on how to safely apply sewage sludge to fields, which was controversial at the time. And back in the energy crisis of the 1970s, he studied the impact of harvesting corn stalks for bioenergy.

That work has been "rediscovered in the last eight or 10 years," Baker said, as the Department of Energy and others have grown curious about alternative energy.

"Bill's research, among others, has been very useful in sounding a cautionary note," Baker said, because it showed corn residue plays an important role in protecting against erosion.

Daughter Suzanne Larson of Long Beach, Calif., said her father "inspired a sense of intellectual curiosity and scientific thinking" among his four children. She was trained as a mathematician, her older brother is a physician and another brother was a trained chemical engineer.

But they did poke fun at dear old dad and his earthly obsession, she said.

"We'd say we were going outside to put plants in the dirt," she said. "It was a running joke in our family. It's not dirt — it's soil. We were going to turn the soil."

It's a turn of phrase known well among scientists, Baker said, who abide the motto: "Dirt is soil that is out of place."

In addition to his daughter Suzanne, survivors include wife, Ruthelaine Larson, and children Larry Larson of Mankato, Steve Larson of Galena, Ill., and Kathy Nesler of Eagan.

A memorial service will be held at 11 a.m. Friday at Presbyterian Church of the Way, 3382 Lexington Av. N. in Shore­view.