No silver bullet to meet N reduction goal
STANHOPE – For farmers to meet their part of the Iowa Nutrient Reduction Strategy, there is no silver bullet.
“But we do have silver buckshot,” said Matt Helmers, an Iowa State University ag engineer, speaking Dec. 11 to an audience of 65 in Stanhope.
He was one of five presenters at an ag drainage school, attended by farmers and farm tile consultants and equipment suppliers.
Helmers outlined the various field practices designed to reduce the amount of nitrates and phosphorus that get into Iowa’s surface waters.
At issue is how farmers will help the state in reaching its INRS goals – nitrates by 41 percent and phosphorus by 29 percent.
These levels were mandated in March 2013 by the U.S. Environmental Protection Agency to diffuse the Hypoxia Zone in the Gulf of Mexico, as both nutrients are carried there through the Mississippi River Watershed.
Nitrates escape fields primarily through tile lines and phosphorus through topsoil erosion.
Helmers identified a dozen measures farmers can adopt to keep nutrients in their fields. None of them by themselves will meet the EPA’s mandate, he said, but combining several practices will get the job done.
The practices are altering the timing of fertilizer applications, variable rate applications of fertilizers, mixing nitrification inhibitors, planting cover crops, convert marginal crop land to pastures, planting perennial energy crops, extending rotations, control water drainage, shallow tile installation, wetland restoration, installing bioreactors and saturated buffers.
Of the 12, Helmers focused on edge-of-field practices – wetlands, buffers and bioreactors – to keep nitrates in place.
“The simplest answer to meeting the EPA mandate,” Helmers said, “is to stop farming and let all the land go back to prairie.
“But I don’t see that happening.”
He said the next step is keeping nitrate-ladened runoff from reaching streams and rivers.
One method is installing water control structures that can be manipulated to drain as much excess water following rain events, while keeping some of it back for crops during dry times. Holding back tile water keeps nitrates in place and available for plant nutrition, he said.
However, these structures, Helmers said, are not cost-effective for fields with more than a 1 percent slope.
That’s why edge-of-field practices are more attractive for most of Iowa’s farm land.
By channeling runoff into a restored wetland, Helmers said, water is kept in place above ground, generally 6 to 18 inches deep, long enough for bacteria to break down some or all of the nitrates before it reaches waterways.
Kapil Arora, an ISU ag engineer, said restoring areas that were wetlands in the past is becoming the preferred land management practice to meet the INRS goals.
Bioreactors and saturated buffers do the same job of denitrification as wetlands, only they are more limited in the water they take in and the process is accomplished underground.
“It’s not a simple thing to meet the goals,” Helmers said, “but it can be done.
“And I think it’s going to take public and private investments.”
Bruce Atherton, an ag engineer housed in the Ankeny office of the Natural Resources and Conservation Services, discussed a series of cost-share programs available to farmers to implement different field practices, including planning, installing, managing and controlling drainage; installing bioreactors; creating saturated buffers; restoring wetlands; and planting cover crops.
“How many acres will have to be treated to reduce nitrate loading?” Atherton asked the audience.
His answer: “Nearly all of them.”
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