Pound for Pound Nitrogen Management

Ken Janovicek, University of Guelph
Greg Stewart, OMAFRA Corn Specialist

Adjusting nitrogen rates based on the price of com and the cost of nitrogen has never been very appealing. However, research from both Illinois and Ontario suggest that ignoring these factors in 2006 may impact your bottom line.

Nitrogen rates for corn should be reduced when either nitrogen fertilizer prices are unusually
high or corn prices are unusually low. Unfortunately, for 2006, nitrogen fertilizer prices are likely to remain at historic highs and corn prices are likely to remain unacceptably low, both of which suggest that optimal nitrogen rates for 2006 will likely be lower than the optimal rates of a few years ago. It is worth examining optimal nitrogen rates for corn in Ontario as related to changes in nitrogen fertilizer and corn prices, and how Ontario adjustments compare to those recently suggested for Illinois.

Historically, nitrogen rate recommendations in Ontario have been calculated at price ratio 5, which means that the value of a pound of nitrogen is 5 times greater than a pound of corn. So, when nitrogen fertilizer was $0.30 per pound of N, at price ratio 5 the value of corn was assumed to be $0.06 per pound or $3.36/bu. The value of corn is based on the expected selling price with drying, storage and handling charges deducted and any government support payments added.

At nitrogen prices of $0.45 to $0.50 per pound of N, the value of corn would have to be $5.04 to $5.60/bu for price ratio 5 nitrogen recommendations to be the most economical for a farmer to use. We will stop here to make one thing clear. When we refer to "most economical rate of nitrogen" or "optimal rate" it will generally not be the nitrogen rate that generates the highest corn yield on your field. It is the nitrogen rate that balances revenue from yield and expenses from nitrogen to produce the highest economic return.

Unfortunately, if the value of your 2006 corn crop is going to be in the range of $2.50 to $2.80/bu, then optimal nitrogen rate recommendations for 2006 should be based on a price ratio of 10. Based on Ontario research data, optimal nitrogen rates are reduced by 5 to 6 lb-N/ac for an increase in price ratio of 1. So, optimal nitrogen recommendations at price ratio 10 are about 25 to 30 lb-N/ac less than at price ratio 5.

A recent extension release from the University of Illinois (E. Nafziger and R. Hoeft) suggested, based on their nitrogen rate trials, that optimal nitrogen rates are reduced by about 7 lb-N/ac for a price ratio increase of 1. The suggested optimal nitrogen rates for corn following soybeans for various price ratios in Illinois are presented in Table 1. The average yield for the Illinois trials at optimal nitrogen rates were in the 170 to 173 bu/ac range.

Table 1 also contains two sets of preplant nitrogen recommendations for corn following soybeans on loam soils in Ontario at various price ratios. Since a yield of 170 bu/ac is not an unreasonable yield expectation for loam soils in the Chatham-Kent region, the 3250 CHU example is based on an expected yield of 173 bu/ac in order to provide a direct comparison of potential Ontario and Illinois nitrogen rate recommendations for various price ratios. It is clear that nitrogen rate recommendations for higher heat unit regions of Ontario are similar to those suggested for Illinois and include similar adjustments for price ratio.

The 2800 CHU recommendations are based on an expected yield of 140 bu/ac which results in recommendations that are about 45 lb-N/ac less than those for the 3250 CHU example. Ontario N recommendations are adjusted for expected yield by a factor of 0.8 lb-N/bu which reduces the 2800 CHU recommendations by 25 lb N/ac. Also, Ontario N trial research indicates that corn produced under similar conditions and expected yields requires about 20 lb-N/ac less N for the 2800 CHU region when compared to the 3250 CHU region. The lower nitrogen requirement for the 2800 CHU region is due to the combination of lower expected yield and less apparent nitrogen requirement in lower heat unit regions.

Based on reasonable projections for nitrogen fertilizer and corn prices in 2006, both US corn belt and Ontario nitrogen trial research support the idea that nitrogen rates should be reduced. If your nitrogen cost this spring is between $0.45 and $0.50 per pound of N, the Ontario nitrogen recommendations presented in Table 1 at price ratio 5 are appropriate only if you expect the value of corn to be between $5.04 to $5.60 per bushel. However, if you expect the likely value of the 2006 corn crop to be in the $2.50 to $2.80 range, then the price ratio 9.8 recommendations in Table 1 are the most appropriate.

Growing corn profitably in 2006 will be a challenge. Using the best information at your disposal to apply the most economic amount of N fertilizer is an option you can't ignore.

Notes:
1) The source of Illinois data is Emerson Nafziger and
Robert Hoeft of the University of Illinois. Full article can be viewed at http://www.ipm.uiuc.edu/bulletinlarticle.php?id=410
2) Current Ontario nitrogen recommendations for your specific corn production practices and farm location can be calculated using a corn nitrogen recommendation calculator which can be downloaded at http://www.gocorn.net