A huge organic farm that's backed by General Mills is facing accusations that it's doing more environmental harm than good. The project shows the difficulties of delivering on green promises.

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Lots of big food companies are going green, promising environmental sustainability, but delivering on those promises can be complicated. And one example is an organic megafarm in South Dakota backed by the company General Mills, maker of Cheerios. Some of the farm's neighbors are accusing the farm of doing more harm than good. NPR's Dan Charles has the story.

DAN CHARLES, BYLINE: Gunsmoke Farms is huge. It covers 53 square miles near Pierre, S.D. An investment fund based in San Francisco and Texas bought it a few years ago. And General Mills announced it would help convert it to organic farming with the help of Gary Zimmer, an organic expert from Wisconsin.

GARY ZIMMER: My job as a soil consultant was to get those soils rich. We were going to fix the soil. And it was going to be quite a large investment. General Mills even took some soil to California to some show (ph) to see what it looked like today and what it was going to look like when we got done.

CHARLES: But in South Dakota, some were skeptical that it could work, including Dwayne Beck, a soil scientist who runs an agricultural research station for South Dakota State University, 40 miles east of Gunsmoke Farms.

DWAYNE BECK: It scared me because normally, organic entails using lots of tillage. And these soils are very fragile.

CHARLES: Farmers often till soil, stir it up with tools like chisel plows or disks to clear weeds and get land ready for planting. But Beck says tillage is destructive, especially where Gunsmoke Farms sits, where it's dry and the soil is full of clay.

D BECK: Once you disturb it, nothing holds that soil together. It just turns into powder.

CHARLES: It can wash away or blow away, which used to happen all the time. There were dust storms so thick cars crashed because drivers couldn't see, so most farmers in this area cut way back on their tillage. Instead, they use planting equipment that slices right into undisturbed land and places the seed into the ground.

D BECK: We'd prefer to not touch the soil at all if we can get by with it, but we have to have some way to put the seed in there.

CHARLES: To control the weeds, they use herbicides. But herbicides are not an option for Gunsmoke Farms, being organic. And last year, to get ready for its first crops of wheat and peas, those enormous fields were tilled. And Dwayne Beck says his fears were realized. He sent me some pictures.

D BECK: Yeah, that's just another picture of soil in the ditch. That's supposed to be green grass.

CHARLES: It's covered by a small drift of windblown dirt. In another photo, a country road disappears into a cloud of dust.

D BECK: That soil that blew out of there, it will never be the same as it was before it blew.

CHARLES: It won't have the stability and structure of healthy soil held together by the roots of plants. When Gunsmoke Farms was just starting, experts from the U.S. Department of Agriculture drew up a soil conservation plan for the farm. They wanted wide strips of permanent native grasses crossing the fields and crops you don't have to plant every year on the steepest hillsides. Gary Zimmer, the soil consultant, says that was part of his original plan. But new farm managers took over and never followed through.

ZIMMER: Oh, boy. Oh, boy. Oh, boy. It's in a deep hole. I don't know how you get it back out organically. It's hard to farm organically if you do it really well and you got your intensive management. But 30,000 acres poorly managed is a really good sign for failure.

CHARLES: General Mills said in a statement that turning Gunsmoke Farms into a thriving ecosystem is a journey, and it promised continued efforts to minimize erosion and improve soil health there. The investment firm that owns the farm, Sixth Street Partners, said in its statement that the farm is early in the process and that its mission, organic farming, also provides benefits like reduced use of pesticides and synthetic fertilizer. Ruth Beck, who's married to Dwayne Beck, used to work for South Dakota State University, advising farmers in this area. She says it's just really hard to grow crops organically on a large scale in this part of the country.

RUTH BECK: You know, we've got to figure out ways to do that, if that's what people want, but we aren't there yet.

CHARLES: At Gunsmoke, she says, environmental marketing got ahead of what farmers can actually do.

Dan Charles, NPR News.

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