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Nitrogen Best Management Practices: You May Need Them More In 2004

Robert Hoeft
Robert Hoeft
Professor of Soil Fertility
Department of Crop Sciences
(217) 333-4424; rhoeft@illinois.edu

The nitrogen used in the production of anhydrous ammonia comes from the very air that you breathe. Since it is easy to “mine,” all nitrogen fertilizers should remain cheap. Wrong answer. The nitrogen is “cheap” torecover, but the hydrogen (Figure 1) connected with it is getting much more expensive. U.S. ammonia production is based on hydrogen from natural gas, a product that is projected to be in short supply for this coming season. As of the end of June, stored supplies of natural gas were about 30 percent below the average for the last five years, and, as a result, natural gas prices are in the $6.00 range, compared with $3.65 a year ago. Ammonia production requires about 30,000 MMBTU of natural gas per ton, so for each $3.00 increase in gas price, the cost of production of ammonia is increased about $90.00 per ton.

Anhydrous ammonia synthesis
Figure 1. Anhydrous
ammonia synthesis.

All of this points to higher prices and a reduction of domestically produced nitrogen for the 2004 season. Since all nitrogen products are derived from ammonia, the price increase will be across the board. The only mediating factor: Foreign producers are not experiencing this sharp increase in gas prices, so there will likely be more urea and UAN solutions coming into the U.S.

Even with the higher cost, nitrogen is an essential purchase for any field that grows corn (Table 1). These data suggest a reduction of about 6 to 7 lb. of N per acre for each 5-cent increase in the price of N per pound, which is equivalent to an increase of $82.00 per ton of ammonia. In both rotations, adjusting the N rate downward to accommodate a 5-cent increase in the cost of a pound of N will result in a yield decrease of only about one bushel per acre.


Table 1. Effect of changing nitrogen price on rate of N needed to attain economic optimum yield and
the effect on yield of changing the N rate. Since the locations used in the continuous corn studies were
not all the same as those used for the corn-soybean studies, one cannot use the data in this table to
determine the N reduction appropriate for corn after soybeans.
Ammonia Nitrogen CORN-CORN SOY-CORN
Price ($/ton) Cost ($/lb.) Optimum N Yield @ opt N Optimum N Yield @ opt N
$230 0.14 161 150 146 170
$312 0.19 155 150 139 169
$394 0.24 149 149 131 168
$476 0.29 143 148 124 167
$558 0.34 136 147 117 166
$640 0.39 130 146 110 164
$722 0.44 124 145 102 163

This projected price increase plus concern about the environment means that we must make sure that we are using nitrogen as efficiently as possible—in other words, that we are using the Best Management Practices:

  1. Apply the proper rate. The best guide that we have is to apply 1.2 lb N/bushel of proven yield, and then take credit for soybeans and other nitrogen that might be applied such as manure, DAP, starter N, 28%N applied with herbicides, and so on. If prices are higher, you may want to lower the N rate slightly.
  2. Apply at the right time for your soil type. While sidedressing is often the most desirable time, there are soils where spring and even fall application will result in as high an efficiency of N use and as low of an environmental risk as sidedressing.
  3. Use the best application technique for the material.
  4. Use monitors to insure accurate application rates.
  5. Use nitrification inhibitors to reduce the rate of conversion of ammonium to nitrate.
  6. Use good crop management practices.

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