Agronomists from the University of Illinois have developed a new approach for making nitrogen (N) rate recommendations on corn that will help growers deal with the recent sharp increases in N prices. This method uses research data from some 250 N rate trials in Illinois and applies economics to the decision on nitrogen rates.
"The proven-yield method used in recent decades to recommend N rates for corn in Illinois tends to set rates higher than the amounts needed to maximize the return to the investment in N," says Emerson Nafziger, crop scientist with U of I Extension. "This is especially noticeable when corn follows soybeans, yield levels are high, and the N price increases while corn prices stay low."
The guidelines will allow growers to apply their N on corn within a defined range of rates. "The ranges are based on calculations using recent research data," Nafziger says. “The recommended range is defined as the rate that provides returns close to the maximum return for a given set of corn and N prices."
For corn following soybean, the range is 122 to 162 lbs. of N per acre when the corn price is $2 and N costs 30 cents/lb. For corn following corn, the recommended range using the same prices is 137 to 174 lbs. of N per acre.
"The recommended range changes when the price ratio between nitrogen and corn changes," Nafziger says.
He notes growers can still think of soybean as providing N to the next corn crop, since the recommended N rate for corn following soybean is lower than for corn following corn.
"If we calculate separate ranges based on the data, the nitrogen rate ranges for southern and central Illinois are very similar, but rates for northern Illinois surprisingly are less than those for the rest of the state," Nafziger says. "This may be a result of more livestock production and generally higher organic matter, which supplies some N to the crop."
Nafziger points out that the ranges in the northern part of Illinois are similar to those reported for Iowa. Until there is more data to confirm this difference, the same recommended range will be applied for all of Illinois.