High fertilizer prices and heavy rainfall in many parts of Missouri are complicating nitrogen management in corn, said University of Missouri Extension state nutrient management specialist John Lory.
Growers should evaluate the return on investment before applying rescue nitrogen, he said.
Excess rainfall saturates soils, leading to nitrogen losses. Rescue nitrogen refers to an unplanned additional application used when corn yellows because of nitrogen loss.
Historically, rescue nitrogen applications were almost always profitable.
“Corn plants that are deficient in nitrogen will always increase yield, even when the application is applied after tasseling,” Lory said.
Because of high fertilizer prices, however, rescue nitrogen requires more yield response to pay off.
“Rescue nitrogen can still pay, but the decision is more field-specific than when fertilizer was cheaper,” Lory said.
To determine whether a rescue application will pay, Lory recommends starting with a simple breakeven calculation: nitrogen price per pound multiplied by pounds of nitrogen applied, plus application cost, divided by corn price.
For example, if nitrogen costs $1 per pound and 50 pounds are applied per acre, plus $10 per acre in application costs, the total is $60 per acre. With corn priced at $4.50 per bushel, the breakeven response is about 14 bushels per acre.
Previous research from MU Extension showed an average yield response of 35 bushels per acre, but variability is high, Lory said.
Nitrogen loss is often uneven, meaning some parts of the field are severely deficient while others still have adequate nitrogen. That makes it harder to predict the overall value of a rescue application.
Lory also said the value of rescue nitrogen is not linear. The greatest return per pound typically occurs in the most deficient areas.
Fields with clear, widespread nitrogen loss will benefit from rescue nitrogen, Lory said. If the situation is uncertain, a lower nitrogen rate may be the safer economic choice, and the first pounds of nitrogen usually deliver the greatest return.
Research from MU Extension shows corn can respond to nitrogen later than many producers expect, even after tasseling.
“The crop will often have no yield loss if rescue applications occur before tasseling; applications after tasseling will still increase yield,” Lory said.
For more information, contact a local MU Extension agronomist or review the Rescue Nitrogen Brief at muext.us/RNB.
