<b>By LINDA McGURK<br>
Indiana Correspondent</b> </p><p>

COVINGTON, Ind. — With nitrogen fertilizer costs on the rise, growers need to critically evaluate their fertilizer programs and consider moving away from the prevailing yield-driven nitrogen application rate recommendations.</p><p>
That was the take-home message from Bob Nielsen, Purdue University extension agronomist, during a Dec. 4 Bi-State Ag Group crop seminar in Coving-ton, Ind. “Apply-ing ‘more than enough’ (nitrogen) is no longer viable, or particularly environmentally friendly,” he said.</p><p>
The traditional rule of thumb recommends that growers apply one pound of nitrogen per bushel of expected yield for a corn-soybean rotation, and 1.2 pounds of nitrogen per bushel for corn following corn or wheat. Now, Nielsen said there’s a regional movement away from this approach toward more data-driven recommendations that factor in nitrogen and grain prices.</p><p>
“Yield response to N is actually a non-linear relationship,” he said. “You get the most return from your first 50 pounds of N and the least return from the last pounds of N. Consequently, applying more N doesn’t necessarily result in bigger yields. The question is where you should stop putting on N and where you start losing money.”</p><p>
The traditional approach, also known as the Agronomic Optimum N Rate (AONR), defines the nitrogen rate that will produce maximum yield, regardless of cost. As an alternative, Nielsen encouraged growers to use the Economic Optimum N Rate (EONR), which defines the nitrogen rate that will give the maximum dollar return. “This new approach requires an awful lot of data and, until recently, what we had available in Indiana was pretty old,” Nielsen said.</p><p>
That’s about to change, since Nielsen and Jim Camberato, also a Purdue extension agronomist, started new nitrogen application field trials across the state two years ago. They’ve conducted 56 trials and are compiling a database.</p><p>
For corn following soybeans, the trials indicated an average AONR rate of 167 pounds of nitrogen per acre, yielding an average of 188 bushels per acre. The average EONR, on the other hand, was only 140 pounds of nitrogen per acre, yielding an average of 186 bu./acre. The calculation was based on $3.25-per-bushel corn and $0.50-per-pound nitrogen.</p><p>
“A hundred and forty pounds per acre may be lower than many of you would feel comfortable with, but that’s what the data is telling us,” Nielsen said.</p><p>
As is true with many things, he acknowledged “the devil’s in the details” when it comes to nitrogen application rates, and the AONR deviated up to 35 pounds from the average in any given location. The difficulty of predicting long-term weather and, consequently, nitrogen loss continues to be a challenge, but farmers can take certain steps to minimize their risk. Anhydrous ammonia is the least risky form of nitrogen and Nielsen recommended applying it in the spring rather than the fall.</p><p>
“As a rule of thumb, you need to assume about 15 percent loss of anhydrous, but sometimes it’s bigger than that,” he said. “If it’s wet prior to application, you’ll have more loss and might need to bump N by 30 pounds. If it’s a dry year prior to application, you’ll have less loss and may want to consider decreasing N by 30 pounds.”</p><p>
Nielsen said nitrification inhibitors can be used to slow the conversion of anhydrous to nitrate, which is more prone to leaching. He also advised using urease inhibitors to reduce the risk of volatilization loss, and sidedressing nitrogen to minimize the time frame for loss.</p><p>
“Nitrogen management is a crapshoot, but if you understand the rules, you increase your chances of winning,” said Nielsen, adding Purdue needs volunteers for on-farm nitrogen management trials.
Growers interested in participating should contact Nielsen at 765-494-4802 or e-mail at rnielsen@purdue.edu