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Public Radio's Environmental News Magazine (follow us on Google News)

Keeping Soil in Its Place

Air Date: Week of

Jane Fritz reports from southern Idaho on the results from use of a polymer commonly called PAM which appears to keep soil from eroding with no known adverse side effects.


CURWOOD: The Snake River faces more environmental perils than the threatened extinction of the salmon. Much of its water is used to irrigate agriculture. When the water runs off the land back into the river, it often carries with it valuable topsoil as well as pesticides and fertilizer. The result is soil erosion, sedimentation, and pollution. Of course, this is hardly limited to the Snake River. Literally billions of tons of topsoil are washed away every year by farmers irrigating fields all over the world. And that causes grave harm to our long-term ability to grow food. But the eyes of agronomy are now on southern Idaho, where an intriguing experiment in soil protection is taking place in the valley of the Snake River. A chemical is being tested that binds irrigated soil and prevents it from being washed away. Jane Fritz brings us this report.

(Water flowing)

FRITZ: The powerful Snake River winds across southern Idaho, cutting a deep gorge through what's known as the Magic Valley.

Irrigation from the Snake has transformed this sagebrush desert into some of the most productive farmland in the country. Beans and sweet corn grow here, potatoes and sugar beets. But since much of the valley farmland is furrow irrigated, muddy runoff from farmers' fields typically drains back into the river. It carries topsoil, nutrients from fertilizers, and chemical pesticides, putting the Snake River's water quality on the critical list. Farmers have used varied methods to reduce irrigation erosion, sediment ponds that hold runoff until it settles and clears. Mulched furrows that help keep soils in place. And manmade wetlands that filter and clean the wastewater. But last summer, farmer Tom Tverdy of Buhl, Idaho, tried the newest solution.

TVERDY: Here's a little bag of it right here. It's some left from last year. It' really quite interesting material. When you put it on, you'd swear that there just wasn't hardly anything going on.

FRITZ: Mr. Tverdy added the polymer, poly-acrylamide, to hundreds of acres of sweet corn that he grows for Green Giant Foods. He used the chemical late in the season and was surprised by the results.

TVERDY: I waited for about, oh an hour, maybe an hour and a half. My brother was in the shop here. And so I went down to the bottom to see what it was like. And pretty soon he came down there. And it looked just like you could have taken that water right out of the well. It looked just like well water. It was really kind of amazing. This is going to revolutionize our little way of irrigating here.

(Running water)

FRITZ: Across the Magic Valley from Mr. Tverdy's farm a team of soil scientists for the U.S. Department of Agriculture's Research Service is in its sixth year of studying the effects of poly-acrylamide -- or, more simply, PAM -- on furrow-irrigated lands.

SOJKA: We're standing in the middle of a potato field that's being furrow irrigated.

FRITZ: Dr. Robert Sojka is co-leader of the PAM research team for the USDA Kimberly Station.

SOJKA: And we're standing between 2 furrows. The one on our right has been irrigated with water the way any normal farmer would. It's untreated water, it comes from the Snake River. And the water coming off this furrow looks about like a chocolate milkshake. You can't see the bottom of the furrow. We're losing a lot of soil. This is a problem.

FRITZ: By mixing a couple of handfuls of PAM in the first run of irrigation water, Dr. Sojka finds that erosion is reduced on this 3-acre test plot by better than 95%.

SOJKA: If we look over our left shoulder we can look through the water of this furrow and actually see the bottom of the furrow. It's completely clear. This water has been polymer treated, and it has completely stopped the erosion in the furrow. Irrigating this way is a sustainable practice. It prevents erosion. A farmer could continue to farm this field this way for hundreds of years because of the fact that the soil that we're looking at today will still be here then.

FRITZ: With just a small amount of the chemical in the water, PAM causes the soil particles to gather, clump together, and fall out of suspension.

SOJKA: The beauty of using this polymer is that we're not fixing a problem after it's happened; we're preventing the problem from happening in the first place. The water is not causing any erosion, so the soil stays put wherever it is in the field. We don't have to come back at the end of the year and clean out a pond, or we don't have to do any tillage to move soil around. The soil basically stays where it belongs in the field.

FRITZ: And with PAM, the soil holds water better, so farmers may be able to irrigate less. For decades PAM has been used in various ways, including food processing and wastewater treatment. It's been approved by the FDA and the EPA. That may be why this new use for PAM isn't raising many eyebrows among environmentalists, but Ken Cook, President of the Environmental Working Group in Washington, DC, does have some concerns.

COOK: It's pretty rare that you find a silver bullet in modern agriculture. It's pretty rare that you find a technology that doesn't have some side effects of one kind or another. In the case of PAM, we really don't know what those may be yet. It clearly is promising when used correctly for erosion control. But are there other effects? We don't know.

FRITZ: Cook wants researchers to closely monitor agricultural use of PAM.

COOK: We've come to learn from lots of past experience in agriculture and in other industries that sometimes there are second generation effects of these technologies that weren't anticipated at the time, and that become evident as they're being used over years and years.

FRITZ: He's particularly concerned about the chemical leaching into ground water and finding its way into rivers and streams. But Dr. Rick Lentz, the other leading USDA researcher, claims PAM is not a ground water threat. Nor does it move far from the farmer's fields.

LENTZ: Basically all the PAM is captured in the upper quarter inch of the topsoil in the furrow. Within several hundred feet or a little over a thousand feet, depending on the time of year, the PAM will be gone. So there's very little threat of the PAM ever reaching surface waters in that case.

FRITZ: And the research team says it hasn't been able to find any negative impacts of PAM on either the soil structure or its productivity. And Bob Sojka notes that PAM also keeps phosphates and nitrates from fertilizers and pesticides in the field rather than in the river.

LENTZ: It's the only case I can think of in which the chemical we're adding results in the removal of more polluting material than it results in adding to it. Yeah, it's a chemical fix. It is a chemical. But in the sense that this is a chemical to be dread, no, I don't think so.

FRITZ: The USDA will continue to study the long-term effects of PAM. This past year PAM went commercial and farmers throughout the western states are now using the chemical as their latest weapon against soil erosion.

TVERDY: It's going to be a great thing for us.

FRITZ: Farmer Tom Tverdy is hopeful about future irrigation treatments with poly-acrylamide. He says in addition to the environmental benefits, using PAM is affordable and not as labor-intensive as some of the other conservation practices he and his neighbors have used.

TVERDY: Nobody wants to have a bunch of dirt going down the river. I mean that's just not how we like to do business. You know, they usually say things sound too good to be true and they usually aren't, so we'll just have to wait and see what happens here. If it doesn't work out as well as we hoped, or if there are side effects to it, then we're going to have to plan something else. But at least there might be a way to fine-tune this somehow to make it work.

FRITZ: Poly-acrylamide may be poised to revolutionize farming in Idaho's Magic Valley, and with a couple billion tons of topsoil lost globally each year to furrow irrigation, maybe the rest of the world is next. For Living on Earth I'm Jane Fritz in southern Idaho.



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