No. 22 Article 6/September 1, 2006

Nitrogen Rates for Corn in Illinois, Fall 2006

The nitrogen rate calculator for Illinois located at the Iowa State University website was updated this summer, and it now includes separate calculations for northern, central, and southern Illinois. We also added a handy feature that allows N price to be designated either per lb of N or as product price per ton.

It's difficult to see, but in the lower right-hand corner of the "manila folder" on the website is some small print that says "How to use." Click on this for a popup that gives information about the site, the rationale used to develop this approach, and a map showing how we divided Illinois into north, central, and south. We know that these designations are less than exact, but they should work until we have data to define regions better.

This approach allows us to use current research data to suggest a range of N rates for a given set of corn and N prices. The good news is that N prices have moderated some since last winter and spring, and projected corn price for the 2007 crop might be higher than recent corn prices have been. How to guess at a price for the 2007 crop when making decisions on how much N to use this fall is not an exact science. If it helps, cash bids in central Illinois this week are running at about $2.05, the December 06 futures price is about $2.40, and the December 07 futures prices is around $2.90.

Table 2 gives suggested N rate ranges for corn following corn and for corn following soybean for different regions in Illinois, at three N prices and five corn prices. The N prices of 25, 30, and 35 cents per lb are equivalent to anhydrous ammonia prices of $410, $492, and $574 per ton, respectively. Ranges for prices between these can be estimated. The N rate expected to provide the greatest return to N is in about the center of each range.

These guidelines are based on the best available data we have, but we hope to add to our confidence in them as we add to the numbers of locations we have to use in the calculations. Until then, we suggest setting N rates within these ranges based on corn and N prices. For corn following corn in fields where continuous corn has been yielding well, it may be appropriate to be toward the upper end of the range indicated.

We continue to get questions about the wisdom of fall application, and about the need to use N-Serve if applying N in the fall. On medium-textured and heavy soils, there is no strong indication that fall application leads to a great deal of N loss, as long as care is taken to apply N only after the soil temperature has reached 50 degrees or less. In practical terms, that means waiting until about the last week of October in northern Illinois and the very end of October or early November in central Illinois. A stabilizer (N-Serve) can provide additional safety against loss, in the event that soils warm up again before they freeze up.

Calling For N Rate Volunteers

You might recall that we asked last winter for cooperators to take part in a project where we hope to get as many as 100 on-farm N rate trials, with N applied in replicated strips. Dr. Howard Brown with Growmark has been a full cooperator on this work, and we have funding from FREC (fertilizer checkoff dollars) to run these trials, probably for at least two more years. Cooperators will be paid a small stipend to compensate for lower yields in low-N strips.

There are about 50 of these trials on Illinois farms in 2006. The trials have gone well, and we will report on results after they come in. We would like to double the number of trials for 2007. We are interested in having trials with fall-applied N and others with spring-applied N, depending on which practice cooperators are using. There are five N rates--0, 50, 100, 150, and 200--with three reps (strips) of each rate, randomized within three blocks, for a total of 15 strips. Strips with N applied before planting (fall or spring) will have to be in the same direction as the rows will be planted, of course, with reasonable assurance that strips where yield will be taken are fertilized uniformly with the correct N rate. Autosteer might help, but it is not required.

Additional N, for example that in DAP or MAP, can be used, meaning that the lowest rate might be 20 to 30 lb of N instead of zero. We would like to get 25 or more of these trials in corn following corn, and the rest in corn following soybean. Fields should not be ones where manure has been applied in the past 10 years.

If you or someone you work with has interest in conducting one of these trials, please contact one of us by email, or phone 217-333-4424. We'll provide additional details in the October issue, and again next spring.--Emerson Nafziger and Fabián Fernandez

Close this window