New nitrogen application calculator and best management practices for the 2009 corn crop

By David Nicolai, University of Minnesota Extension

With substantial increases in the prices of fertilizer nitrogen, farmers are encouraged to re-evaluate their nitrogen rates for corn for the greatest economic return on their investment. A handy, simple, and convenient tool to help Minnesota corn growers arrive at the optimum economic nitrogen rate is the “Corn N Rate Calculator” found on the Iowa State University website at http://extension.agron.iastate.edu/soilfertility/nrate.aspx. The revised and updated CRNC now contains yield data from replicated studies at 128 sites in 25 Minnesota counties from 1990 through 2007.

The calculator is easy to use requiring the user to enter their state, type of fertilizer, price per ton and expected corn price per bushel. The calculator will than calculate the maximum return to nitrogen, the N rate where the economic net return to N application is maximized. Users can also enter multiple fertilizer and corn prices at the same time so that they can view and print a comparison of prices.

More detail listing the appropriate nitrogen, phosphorus and potassium fertilizer guidelines can be found in Fertilizing Corn in Minnesota FO-3790-C Revised 2006, available on-line at: http://www.extension.umn.edu/distribution/cropsystems/DC3790.html

In this era of fluctuating high prices, farmers using N rates provided by the on-line Corn N Rate Calculator coupled with other best management practices for nitrogen will be able to obtain the greatest economic return on their fertilizer N investment.

What Are the Nitrogen Best Management Practices?

Best Management Practices for nitrogen are broadly defined as “economically sound, voluntary practices that are capable of minimizing nutrient contamination of surface and groundwater.” The BMPs recommended herein are based upon research conducted by the University of Minnesota from over 70 site-years of field research in south-central Minnesota and upon practical considerations.

The BMPs are based, in part, upon the concept of total nitrogen management, which accounts for all forms of on-farm nitrogen in the development of crop management plans. BMPs were developed to be adopted on a statewide as well as a regional basis. Printed copies of the new BMP guidelines are available at your local county extension office.

BMPs for South-Central Minnesota

South-central Minnesota is characterized by fine-textured soils formed in glacial till and sediments. Most south-central soils have naturally poor-to-moderate internal drainage and are tiled to improve drainage. Average annual precipitation in the region is 27 to 35 inches.

The BMPs are divided into three categories described as: 1) recommended, 2) acceptable but with greater risk, and 3) not recommended. With respect to N management, risks can be either economic or environmental. Economic risks can be either a consequence of added input cost without additional yield or a reduction in yield. Environmental risks pertain to the potential for loss of nitrogen to either ground water or surface waters.

For south-central Minnesota, the BMPs are:

Recommended:
• Select an appropriate N fertilizer rate using University of Minnesota guidelines found at http://www.extension.umn.edu/distribution/cropsystems/DC3790.html
• 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 to a minimum depth of three inches.
• Apply sidedress application before corn is 12 inches tall (V7 stage).
• Inject or incorporate side dress applications of urea or UAN into moist soil to a minimum depth of three inches.
When soils have a high leaching potential (sandy texture), nitrogen application in a split-application or side dress program is preferred. Use a nitrification inhibitor (N-Serve) on labeled crops with early side-dressed N.
• Take appropriate credit for previous legume crops and any manure used in the rotation.
• Spring preplant applications of ammonia and urea or split applications of ammonia and urea or split applications of ammonia, urea and UAN are highly recommended.
• Total N rate should include any N applied in a starter weed and feed program, and contributions form phosphorus fertilizers such as MAP and DAP.

Acceptable, but with greater risk:
• Fall application of ammonia plus N-Serve after soil temperature at the 6-inch depth is below 50 degrees.
•Spring preplant application of UAN.
• Late fall or spring preplant application of coated urea fertilizer.

Not recommended:
• Fall application of urea, UAN, and ammonia without N-Serve.
• Side-dressing all N when corn follows corn.
• Fall application of N to coarse-textured (sandy) soils.
• Application of any N fertilizers, including MAP and DAP on frozen soils.
• Fall application of UAN (28-0-0).

(David Nicolai is an educator-crops with University of Minnesota Regional Extension in Hutchinson.)