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Fall nitrogen applications not recomended in Fillmore County

Fri, Sep 6th, 2013
Posted in All Agriculture

Travis Willford, Harmony

Brian Hazel, Lanesboro

Pamela Mensink, Preston

Tim Gossman, Chatfield

Leonard Leutink Jr., Spring Valley

Fillmore County is among the seven counties in southeastern Minnesota’s karst region where fall application of nitrogen is not recommended by the Minnesota Department of Agriculture (MDA). This recommendation has been in place since 1990 and is based on factors unique to southeastern Minn.

The landscape characteristics due to the karst geology make this area particularly susceptible to ground water contamination. Shallow soils over fractured bedrock allow nitrogen to leach into ground water supplies very easily. Southeastern Minn. also has higher average rainfall which increases the risks of nitrogen leaching.

Once in the underlying limestone aquifers, nitrogen contamination is very difficult and expensive to clean up. Since plants need nitrogen to grow, its use cannot be eliminated, so careful management is key to keeping excess nitrogen out of the ground water.

Ground water is the source for all our drinking water in Fillmore County and in the region. Nitrate, the form of nitrogen found in ground water, is often at concentrations that exceed the drinking water standard of 10 parts per million (ppm) particularly in limestone aquifers closest to the land’s surface. Old, poorly constructed wells are at the greatest risk for having high nitrate water. Babies under 6 months of age and pregnant women should not drink water with nitrate levels over 10 ppm because of the risk of “blue baby syndrome,” which can cause developmental problems for the baby or even death.

Nitrogen lost to ground water is like “money down the drain.” Studies by the MDA and the MN Pollution Control Agency find that the majority of leaching losses occur during the non-cropping season. Fall application puts nitrogen in the soil profile at a time when it is most likely to leach. Ideally, nitrogen applications should be matched to the time when a plant needs the nutrient for growth. This increases yields, increases nitrogen use efficiency (and the resulting cost savings), and decreases the amount of nitrogen leached to ground water. Almost two decades of research by the University of Minnesota has shown that heavy spring rains cause leaching of fall nitrogen applications resulting in nitrogen deficiencies that reduce corn yields by up to 50 bushels per acre. At today’s prices, that is equal to a loss of over $300 per acre.

MDA’s Best Management Practices for Nitrogen Fertilizer Use in Southeastern Minnesota are:


•Select an appropriate N fertilizer rate using U of M guidelines (“Fertilizing Corn in Minnesota” FO-3790, 2006 or newer) which are based on current fertilizer and corn prices, soil productivity and economic risks.

•Total N rate should include any N applied in a starter, weed and feed program, and contributions from phosphorus fertilizers such as MAP and DAP.

•Spring preplant applications of ammonia and urea or split applications of ammonia, urea, and UAN are highly recommended.

•Incorporate broadcast urea or preplant UAN within three days.

•Under rain fed (non-irrigated) conditions, apply sidedress N before corn is 12 inches tall (V7 stage).

•Take appropriate credit for previous legume crops and any manure used in the rotation.

•Inject or incorporate sidedress applications of urea or UAN into moist soil to a minimum depth of three inches.

•Minimize direct movement of surface water to sinkholes.

•When soils have a high leaching potential (sandy texture), nitrogen application in a split-application or sidedress program is preferred. Use a nitrification inhibitor on labeled crops with early sidedress N.


but with greater risk

•Spring preplant application of UAN

•Spring preplant application of ESN

Not recommended

•Fall application of ammonia, urea, and UAN, with or without a nitrification inhibitor (N-Serve).

•Sidedressing all N when corn follows corn.

•Fall application of N to coarse-textured (sandy) soils.

•Application of any N fertilizer including MAP or DAP on frozen soils.

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