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In pursuit of pesticides
By Rebecca Goetz
A trio of Purdue professors have turned into gumshoes of sorts, tracking pesticides that escape farm fields and move into ground and surface water.
In the fields, pesticides do an important job for the farmer, but when they run off into surface or groundwater, they can pose a threat to the populace. By studying pesticide movement and learning more about the lay of the land, Purdue researchers are finding ways to round up the rogues.
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Agronomist Eileen Kladivko tracks movement of pesticides into the earth, looking for evidence of pesticides in groundwater and tile lines. (Photo by Tom Campbell) |
Trickling through drain tiles
Fifteen years of digging for data under her feet has turned agronomy. Professor Eileen Kladivko into an advocate of field tiles.When Kladivko first started tracking pesticide movement in fields, she focused on preferential flow, the movement of water and pesticides directly down into the earth through soil cracks or animal and worm tunnels. She was worried that pesticides might slip through those channels, into the groundwater, or that they would move into tile lines, then spew from tiles into the ditches and streams -- and into surface water.
After a decade and a half of tromping through farm fields and sampling water from drainage tiles, Kladivko has put some of those fears to rest. She's found that, compared to pesticide runoff in surface water from farm fields, relatively little pesticide soaks down through soil into groundwater. Likewise, relatively little moves into surface water through tile lines.
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A pesticide molecule (center) sticks to cations (large blue spheres) on a clay surface. |
In a report she co-authored in 1999 for the American Crop Protection Association, Kladivko analyzed more than 30 studies of tile drainage conducted by researchers from across the country. Data from those studies mirror Kladivko's.
"It's different for different soils, but what we've found is that in most soils the amount of pesticide that gets through (into tile lines) is generally less than half a percent, and often less than two-tenths of a percent, of what is applied," Kladivko says.
This is less than the amount of pesticide carried in surface runoff with eroding soil. Researchers tracking run off from poorly drained fields often find 1 or 2 percent of pesticide applications in surface water during the first or second storm after application.
According to Kladivko, field drainage tiles keep pesticides out of surface water in two ways. First, less water runs off tiled fields, which means less pesticide gets carried away in water. Second, when water percolates down through soil before it runs into tiles, many of the chemical molecules stick to soil particles. Less pesticide is left in the water to get carried away to ditches and streams.
Kladivko's research leads her to counsel farmers to tile poorly drained fields and to use conservation tillage, buffer strips and other erosion-control techniques along the edges of fields to slow erosion.
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