Farmers balancing corn crop needs, soil fertility, fertilizer costs and corn prices have a great tool – the Maximum Return To Nitrogen or MRTN.
Developed in the 2000s, the online tool converts yield responses to economic responses and makes predictions based on in-field trial data, said Emerson Nafziger, University of Illinois professor emeritus in crop sciences and Extension agronomist. Nafziger discussed the benefits of MRTN at the Illinois Fertilizer and Chemical Association Conference, Peoria.
MRTN offers farmers a process to calculate economic return to nitrogen applications with different nitrogen and corn prices.
They can calculate profitable nitrogen rates directly from recent nitrogen rate research data. It follows a regional approach for determining corn nitrogen rate guidelines implemented in Illinois and several other Corn Belt states.
“We developed MRTN because we know nitrogen responses aren’t going to be predictable,” Nafziger said. “I don’t know any way to predict what the nitrogen response will be – even in the same field.”
Nafziger emphasized MRTN is designed to maximize farm income, not yields. “If the goal is to assure maximum yields not maximum profit, then this approach doesn’t work,” he said.
He asked rhetorically, “Why not have farmers base nitrogen rates on their yield goals?” Those don’t work and “we can’t afford that much nitrogen,” he said.
With 2022 prices of $1 per pound of nitrogen and corn prices at $5 per bushel, nitrogen is going to be the biggest expense for corn, according to Nafziger. At those prices, a bushel of corn will pay for only 5 pounds of nitrogen, not the usual 10 pounds, he added.
Nafziger shared an example of a 2021 nitrogen rate trial in a field of corn following soybeans. The nitrogen rate that maximized the yield was 207 pounds of nitrogen per acre that produced 242.5 bushels per acre. But the economic optimum nitrogen rate was 178 pounds of nitrogen per acre, producing a yield of 240.3 bushels per acre.
He defined the economic optimum nitrogen rate as one in which the last pound of nitrogen pays for itself.
In Nafziger’s example, the nitrogen fertilizer cost 75 cents per pound and the corn price was $5 a bushel. Comparing the maximum yield rate with the economic optimum rate was a difference of 29 pounds of nitrogen, costing $21.75, to produce 2.2 more bushels worth $10.90.
“So, we lost $10.85 per acre to put on those last pounds of nitrogen to maximize the yield,” Nafziger said. “Yield-goal based nitrogen rates haven’t worked in more than 284 trials over 15 years.”
It’s time to use MRTN, Nafziger said.
The tool allows a farmer to calculate different prices, compare rates with different nitrogen prices while the corn price stays the same, he explained, adding, “It will give you a range and actual net returns.”
The professor refuted claims that MRTN doesn’t really work.
Some say the tool is a static measure. Nafziger countered the corn and nitrogen prices in the system change and field trial data stays up to date. MRTN information changes as new trial data is added and older data is removed, keeping the information current, he added.
While no two field trials are exactly the same, MRTN “says, ‘This is our best guess,’” Nafziger said. “Obviously, the MRTN rate goes down as nitrogen prices increase.”