If you have winced while writing out a check for your anhydrous ammonia requirements, you will probably be quite interested in using it efficiently, and getting the most for your money. Nitrogen prices are high, and yes, corn prices are high also to provide payback. But no one wants to waste the liquid gold in the white tanks.

Corn prices may have peaked for the time being, but nitrogen prices show no indication of weakening. Your goal should be to apply just enough nitrogen to maximize your yield. While that may seem to have an easy answer, it is one of the most impossible questions in all of agriculture to answer. If you ask, “How much nitrogen should I apply?”; the most honest answer is, “Well, that’s hard to say.” In his recent newsletter, University of Illinois Crop Production Specialist Emerson Nafziger outlines the reasons why your question can’t be answered, but provides some guidance to work through the challenge.

First start with some of the facts that are known, to help put the challenge in context:
• At maturity, corn will have 0.7 lbs. of N in a bushel of grain, about 0.3 lbs. of N in the stalks for each bushel, so a 200 bushel crop will account for 200 lbs. of N per acre.
• There is little correlation between yield and the amount of N that is applied, since efficiency of use can depend upon the amount taken up by the crop, placement, N loss, soil moisture and root growth.
• The organic matter in the soil is a good source of N, but is unpredictable because of microbial breakdown, and that depends on soil conditions, such as moisture and temperature.
• Nitrogen fertilizer needs to make up the shortfall, and since the shortfall is nearly impossible to quantify, the fertilizer requirements remain a question mark. Fertilizer trials have demonstrated that optimum yields can be produced with fertilizer applications ranging from 50 to 250 lbs of nitrogen per ace.

Finding the optimum rate has changed in the past few years, and research shows that it depends on the price of the nitrogen and the price of the corn, instead of the highest yield per acre in terms of bushels. The ratio of prices has remained surprisingly steady at 10 to l. $2 corn and 20¢ nitrogen. $5 corn and 50¢ nitrogen. However, additional research data added each year tends to refine the recommendations, and based on your current cost of nitrogen and what you have 2008 corn booked for at the elevator, it is highly recommended that you utilize an on-line decision aid calculator.

Decision aid calculator for IA, IL, MN, and WI

Decision aid calculator for NE

Decision aid calculator for OH

The calculators may suggest a range of nitrogen application or a midpoint of a range, which provide some flexibility. The recommendations also take into consideration the nitrogen needs of corn following corn versus corn following soybeans. As you make your decision, considerations that may also play into your decision include:
• Application close to the time of use by the corn plant will decrease nitrogen loss.
• Plants take up nitrate, and efforts to keep nitrogen in ammonium form are often unnecessary in the spring if there is a short time between application and use.
• Corn roots are designed to absorb nitrogen, leaves are not. Leaf health is determined more by nitrogen supplied to the roots than to the leaves.
• Corn plants can suffer root burns and death if the nitrogen is applied in the row or too close to the roots, particularly if the soil is dry; so it is recommended that nitrogen be applied between the rows instead of under.
• Urea can deteriorate rapidly, and nitrogen will be lost, if it is applied on a warm, dry surface or if there is excessive crop residue. Incorporation is needed to place the urea where it can be used by the crop, if rain is not forthcoming. Compare the cost of the incorporation to the cost of a urease inhibitor.

Summary:
Nitrogen cost is high, but its contribution to a high value corn crop is priceless. The unfortunate part is not knowing exactly how much nitrogen to apply. Numerous issue impact the optimum application rate, including soil conditions, organic matter, placement, etc. On-line decision aids are available to assist in making a reasonable decision. Good agronomic practices will also assist in efficient use of your resources devoted to nitrogen application.