U of I Develops New Nitrogen Rate Guidelines for Illinois Corn Growers - URBANA - Agronomists from the University of Illinois have developed a new approach for making nitrogen rate recommendations on corn that will help growers deal with the recent sharp increases in nitrogen prices. This method uses research data from some 250 nitrogen rate trials in Illinois and applies economics to the decision on nitrogen rates.

"The proven-yield method used in recent decades to recommend nitrogen rates for corn in Illinois tends to set rates that are higher than the amounts needed to maximize the return to the investment in nitrogen," said Emerson Nafziger, crop scientist with U of I Extension. "This is especially noticeable when corn follows soybeans, yield levels are high, and the nitrogen price increases while corn prices stay low."

The guidelines will allow growers to apply their nitrogen on corn within a defined range of rates.

"The ranges are based on calculations using recent research data," Nafziger said. "The recommended range is defined as the rate that provides returns close to the maximum return for a given set of corn and nitrogen prices." For corn following soybean, the range is 122 to 162 lbs. of nitrogen per acre when the corn price is $2.00 and nitrogen costs 30 cents per lb. For corn following corn, the recommended range using the same prices is 137 to 174 lbs. of nitrogen per acre.

"The recommended range changes when the price ratio between nitrogen and corn changes," Nafziger said. "If the corn price stays the same, the nitrogen rates drop by about 1 ½ lb for each one-cent increase in the cost of a pound of nitrogen. That's about one lb. of nitrogen per acre for each $10 increase in the cost of a ton of anhydrous ammonia."

If the nitrogen price stays at 30 cents per lb., the corn price has to drop by about 33 cents per bushel to drop the recommended nitrogen rate by the same 10 lbs. per acre.

"Because we used data from different trials to define these ranges, there will be separate ranges for corn following soybean and corn following corn," Nafziger said. "The soybean nitrogen credit will no longer be subtracted. Because we use only data from trials where corn follows soybean in the calculations for this rotation, the soybean credit is already included."

He notes growers can still think of soybean as providing nitrogen to the next corn crop, since the recommended nitrogen 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 said. "This may be a result of more livestock production and generally higher organic matter, which supplies some nitrogen 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.

"For corn following corn, there is some correlation between yield and the nitrogen rate it takes to produce that yield, indicating that some adjustment based on yield is justified," he said. "We suggest using the expected yield to move to higher or lower rates, while staying within the suggested range of rates."

He suggests that growers increase the nitrogen rate by 0.4 lbs. of nitrogen for each bushel of yield expected above 150 bushels per acre.

"This is a small adjustment, but it helps to assure high enough N rates in continuous corn fields with high yield potential," Nafziger said. "Producers and advisers will need to decide where to set nitrogen rates within a recommended range. This decision can involve risk-management philosophy, previous experience with N rates, and possible considerations regarding nitrogen movement into the environment."

Source: ACES News - 7th November 2005