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Trapping elusive nutrients

At a packed meeting room in Des Moines, Iowa, members of the Iowa Farm Bureau Federation got a detailed look at the science and the politics behind the new Iowa Nutrient Reduction Strategy Tuesday.
While some other states are considering regulations to lower excess fertilizer that finds its way into streams and rivers, Iowa is one of the first states in the nation to roll out a science-based voluntary plan with an ambitious target: reducing both nitrogen and phosphorus in waterways by 45%. Only one other state, Mississippi, currently  has a nutrient reduction plan. Both are in response to concern about hypoxia in the Gulf of Mexico. Excess nutrients from the Mississippi River enter the Gulf where they encourage the growth of algae and an oxygen-starved dead zone that's hurting the fishing industry.  
When told by a Farm Bureau member that some farmers see the Iowa plan as a first step towards regulation, Iowa Secretary of Agriculture Bill Northey told the group that if it succeeds, it could help farmers avoid red tape.
"This is not a regulatory framework. This is not set up that way, where one size fits all," Northey said. 
In fact, using just one or two approaches likely won't work, according to Matt Helmers, an Iowa State University Extension agricultural engineer involved in a two-year scientific study of practices that could reduce nutrients entering streams. Nitrogen and phosphorous need to be managed differently. Phosphorous finds its way to streams in surface runoff of soil particles while nitrogen leaches below the root zone into groundwater and tile lines before reaching streams. And the source of the "excess nutrients" is also tied to the fertility of the soils themselves and their historical conversion from prairie to one of the most productive farming regions on the planet.
Helmers said that reducing tillage or converting to no-till can reduce phosphorous runoff into streams by as much as 90%. But studies have shown that much of the phosphorous in stream water is coming from bank erosion and stream beds. 
Just lowering nitrogen application rates will have a modest impact. Helmers said that if the amount applied is lowered from the statewide average of 151 pounds of N per acre to 133 pounds, it would reduce nitrogen leaching by 9%. Using nitrogen inhibitors with fertilizer cuts excess nitrogen by 6% to 9% Using cover crops can trap another 31% of nitrogen, but it also brings a risk of lowering corn yields. Wetlands can reduce nitrogen by 52%. 
"To achieve our goal will require a combination of practices," Helmers said.
Helmers said the estimates of savings are based on research, mainly in Iowa, as well as surrounding states. For two years, ISU worked the Iowa Department of Agriculture and Land Stewardship, the state's Department of Natural Resources and USDA on the scientific basis for the nutrient plan.
Iowa's agriculture department is seeking public comment on the strategy through January 4. The strategy can be found here.  
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