PRAIRIE CITY, Iowa -- As scientists, corporations, farmers and environmentalists debate whether genetically modified plants are healthy for humans, a soil and water conservation group says they help the environment.

Biotech crops can reduce the need to plow, resulting in less erosion of topsoil and less air and water pollution, the Conservation Technology Information Center concludes in a study presented Thursday at the World Food Prize Symposium in Des Moines.

The biotech cotton and soybean crops studied by the center have a built-in tolerance to herbicides, decreasing the need to plow, said Dan Towery, a natural resources specialist for the center who co-authored the study.

The CTIC study, a compilation of government and industry data, says no-till acres have increased 35 percent since biotech crops were introduced and now total more than 55 million acres.

The CTIC is a nonprofit organization based in West Lafayette, Ind., that promotes soil conservation and water quality. It receives funding from public and private sources, including agribusiness, foundations and government agencies.

The center promotes no-till and other forms of conservation tillage, in which the surface of farmland is covered with crop residue after planting to limit erosion. The study, done over the past year and a half, says conservation tillage has reduced soil erosion by 1 billion tons per year -- a 30 percent improvement since the early 1980s, Towery said.

"Americans now have cleaner and more affordable drinking water because farmers tripled the number of acres they plant with conservation tillage in the past two decades," Towery said. "We can do even better as more farmers plant biotech crops and convert to no-till farming systems."

Agricultural biotechnology has met with strong consumer resistance in Europe and Japan. A National Academy of Sciences panel said this year that there is no evidence that the genetically engineered crops on the market have caused ecological problems, but that systematic monitoring is needed to ensure the crops are safe.

Some experts are skeptical whether biotech crops encourage farmers to keep plows from the fields.

Mahdi Al-Kaisi, an assistant professor of soil management at Iowa State University, said farmers can benefit from conservation tillage whether they use biotech crops or not.

Kristen Hessler, a bioethics outreach coordinator with Iowa State University, said the study raises ethical questions about planting large amounts of biotech crops.

Gordon Wassenaar, a Jasper County farmer, went to a no-till system in the early 1990s and grows genetically engineered corn and soybeans on his 1,500-acre farm. The results make him want to use more biotech developments, he said.

"We've lost less soil on our farm in the past 10 years than we used to in one year in the go-go '70s when we would plow," Wassenaar said.