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Cropland plays large role in state's nitrogen battle

By Janet Kubat Willette

Date Modified: 10/25/2013 12:59 PM

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ST. PAUL — Agriculture has work to do when it comes to reducing nitrogen levels in the state's rivers and streams.

That's among the conclusions of a "Nitrogen in Minnesota Surface Waters" report released in June. The report was presented to the House Environment, Natural Resources and Agriculture Finance Committee on Oct. 7.

The report found an estimated 73 percent of the nitrogen entering the state's surface water comes from cropland sources and 9 percent is from wastewater point sources. Other sources, including forests, urban stormwater, the atmosphere and malfunctioning septic systems, contribute the remaining 18 percent.

Dave Wall, a Minnesota Pollution Control Agency hydrologist, presented the report, which was written by 15 authors and co-authors. The University of Minnesota led the assessment of agricultural and nonpoint sources of nitrogen.

"This study of nitrogen in surface waters was conducted to better understand the nitrogen conditions in Minnesota's surface waters, along with the sources, pathways, trends and potential ways to reduce nitrogen in waters," the report states.

Nitrate levels exceeded 5 milligrams per liter at 41 percent of monitored sites across the state and exceeded the drinking water standard of 10 milligrams per liter at 27 percent of the sites for the years 2000 through 2010. Concentrations tend to be highest in the southern part of the state.

The nitrogen doesn't stay within the state's borders. Most of the state's nitrogen leaves via the Mississippi River, with 211 million pounds of total nitrogen leaving the state each year, Wall said. Three quarters of that nitrogen originates in Minnesota watersheds.

About 37 million pounds leaves the state via the Red River, with about half from Minnesota and half from the Dakotas.

The Cedar, Blue Earth and Le Sueur River watersheds contribute the most total nitrogen to the Mississippi River Watershed. The 15 watersheds with the most total nitrogen contribute 74 percent of the total load.

Nitrogen loads have increased in the Mississippi and Minnesota rivers between 1976 and 2005.

But not all locations show increasing concentration trends. Two monitored sites on the Minnesota River showed a slight increase in nitrate concentration from 1979 to 2005, followed by a decreasing trend between 2005-06 and 2010-11. From 2009 through 2011, all sites on the Minnesota River have either been trending downward or showing no trend in nitrate concentration.

Concentration levels are determined by taking a water sample and having a laboratory determine how much nitrogen or nitrate mass is in a given volume of water.

Loads are calculated by multiplying nitrate concentrations by the amount of water flowing down the river.

Doug Peterson, Minnesota Farmers Union president, said farmers use nitrogen to maximum efficiency. Nitrogen equals yield, he said.

Farmers Union recognizes that agriculture has a significant impact on the amount of nitrogen in the state's waters and he said the organization will work with its members and the Legislature to focus on solutions.

However, the pollution didn't occur overnight and it will take a lot of effort to change, Peterson said.

It will take a major social commitment to get farmers to rediversify, added George Boody, executive director of the Land Stewardship Project.

Annual corn and soybeans dominate too much of the landscape, he said. More resources need to be focused on putting perennials on the landscape. Continuous living cover provides water quality benefits.

Jim VanDerPol, who farms near Kerkhoven, said agriculture needs to change to reduce the amount of nitrogen leaving the land.

The VanDerPol family changed from a conventional corn-soybean rotation to a certified organic livestock-focused operation with a six-year rotation. His six-year rotation includes three years of hay.

"We learned to start to listen to the farm," VanDerPol said.

He said he goes out during rain events to watch for runoff, to see where water is ponding, and to see where the water is running from. Other farmers need to do the same, he said.

Warren Formo, executive director of the Minnesota Agricultural Water Resource Center, said farmers optimize the use of nitrogen in their fields.

"We're working to improve food security through better farming," he said.

Kris Sigford from the Minnesota Center for Environmental Advocacy said the state's nitrogen problem is not caused by a few bad actors and can't be solved by making a few changes.

The report echoes Sigford's comment: "Appreciable nitrogen reductions to major rives and large downstream waters cannot be achieved by solely targeting individual small subwatersheds or mismanaged tracts of land," the report reads. "However, cumulative smaller scale changes repeated across much of the southern Minnesota landscape can make an appreciable difference in nitrogen loading."

Agriculture is an important part of the state's economy and heritage, but who should bear the costs for cleaning up polluted waters, asked Darrell Gerber with Clean Water Action. Public water suppliers are required to deliver water that meets the 10 mg/l standard.

The report suggests in-field nutrient management, tile drainage management and treatment and vegetation diversification be used to reduce nitrogen losses.

A Nitrogen Best Management Practice watershed planning tool found that a 30 percent to 35 percent reduction of cropland nitrogen losses could be achieved if:

• More than 90 percent of the corn land received optimal fertilizer rates applied in the spring;

• Perennials were planted on 100 feet of either side of most streams;

• All tile drainage water was treated in wetlands, bioreactors or otherwise managed with controlled drainage structures;

• Rye cover crops were planted each year on most row crops; and

•Marginal cropland was planted to perennial vegetation.