Iowa State, partners do farm trials to update nitrogen fertilizer recommendations

Iowa State University is doing on-farm trials on 148 fields across the state this summer to try to find the optimum rate of nitrogen fertilizer to boost corn productivity while avoiding runoff into rivers and lakes.

One of those studies is at Tim Burrack’s farm in Butler County’s Aplington.

“What we’re hoping to find out is can we reduce our nitrogen and still get the same yields,” said Burrack, who grows corn and soybeans. “We believe we can, but the only way you know is if you try it out.”

The research is funded with $1 million in state money allocated by the Iowa Legislature to revise a long-standing fertilizer calculator used in seven corn-growing states.

Background

More than 20 years ago, Midwestern soil scientists, including ISU Professor Emeritus John Sawyer, developed the Maximum Return to Nitrogen (MRTN), a practice that calls for weighing the prices of corn and fertilizer to find the sweet spot of productivity and profit without waste.

They created the Corn Nitrogen Rate Calculator, an online tool that lets farmers in seven Midwest states plug in local prices and get a fertilizer rate recommendation based on scientific field trials in their area.

While the calculator is a guide, many farmers are using too much fertilizer. A 2018 study by University of Iowa researchers showed landowners in two Western Iowa watershed had applied more than double the recommended rate of nitrogen fertilizer — including commercial fertilizer and manure — causing higher nitrate levels in streams there.

The Iowa Farm Bureau criticized the formula used to create the calculator.

“Why is that particular tool and that logic in general, why is that flawed and what’s a better, maybe more informed way, of looking at this issue of nitrogen that in our soil, both naturally and what’s being applied?” moderator and Farm Bureau spokesman Andrew Wheeler asked during a July 26, 2021, podcast.

Rick Robinson, Farm Bureau’s then-natural resources policy adviser, responded: “Many soil scientists say that the long-standing MRTN rate calculator, which estimates the economic return to nitrogen application rates with different nitrogen sources and corn prices, really doesn’t account for weather and soil variability or changes and improvements in genetics and management that we’ve seen over time. That kind of information hasn’t been updated in the MRTN.”

Last year, Iowa Gov. Kim Reynolds approved a plan to spend $1 million to update the “static” Maximum Return to Nitrogen calculator with a “dynamic modeling system that considers variability in the environment, management and weather,” according to the Infrastructure Appropriations Bill.

Researchers concerned about water quality predicted the new recommendations would result in higher nitrogen recommendations. Excess nitrogen can cause the formation of harmful algae that makes lakes unswimmable and can harm drinking water without expensive removal. The nitrogen recommendations also influence the amount of manure allowed to be applied to farm fields from animal confinements.

What’s happened since

The Iowa Department of Agriculture and Land Stewardship, which received the $1 million funding, allocated the money to ISU. The university created the Iowa Nitrogen Initiative, a public-private partnership.

It’s unclear exactly who is in the initiative, but field days this summer have support from the Iowa Corn Growers Association, Iowa Soybean Association, Iowa Agriculture Water Alliance and Verdesian Life Sciences. The alliance includes fertilizer companies, seed retailers, a pork producer and field drainage company, among others.

ISU and its partners are doing 270 on-farm trials this summer on 148 fields, working with 72 farm operators. The results of these trials, done in seven geographic regions of Iowa, will be available in early 2024.

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“These data will be used to update and improve the MRTN,” Mike Castellano, an ISU agronomy professor and principal investigator with the initiative, told The Gazette. “For reference, this is more than a 20-fold increase in the number of trials that contributed to the MRTN before the appropriations.”

Nitrogen fertilizer recommendations now used in Iowa were based on about 10 trials per year, Castellano said. He and his peers plan to use the data they collect and quantitative modeling to create nitrogen recommendations that are more field specific.

The trials this summer involve putting different amounts of nitrogen fertilizer on different parts of a field, explained Burrack.

“When we harvest, it should show up on the combine monitor,” he said. “We’ll be able to determine how those different N rates affected the corn yield.”

ISU will host field days Tuesday through Sept. 6 to talk about the nitrogen fertilizer trials as it tries to recruit other farmers for trials in 2024. The Tuesday event is at 10 a.m. at Burrack’s farm, 8124 Eighth St., Aplington. Other dates and locations are available online. RSVP is required.

Comments: (319) 339-3157; erin.jordan@thegazette.com