The Iowa Nitrogen Initiative will expand its hundreds of on-farm nitrogen rate trials this year to include data on cover crops, residue removal and autonomous applications while also investigating planting dates and tillage control in its effort to improve nutrient efficiencies across Iowa’s farm fields.

The 2024 growing year will mark the fourth season Iowa State University (ISU) has partnered with agricultural service providers, farmers and their advisors on the Iowa Nitrogen Initiative. The first-of-its-kind public-private partnership deploys hundreds of on-farm, scientifically robust small plot trials.

The goal is to expand the program from 270 trials in 2023 to possibly 500 test plots in 2024. 

Iowa Nitrogen Initiative Director Melissa Miller said there’s been impressive data already collected and analyzed in the project’s first years and hopes are to make additional progress this year.

“We are working directly with farmers across the state,” Miller said, “conducting hundreds of on-farm nitrogen rate trials on farmer fields.

“I’d like to see 400-500 trials this year. The more that we have, the better our models are. We want everyone to be able to participate in these trials.”

Miller was joined by ISU soil science professor Michael Castellano and Mitchell Baum, ISU research associate, at the 34th annual ISU Integrated Crop Management Conference earlier this month. The group is encouraging Iowa farmers to consider participating in the 2024 trials, working with ISU on necessary data transfers and nitrogen prescription coding for variable rate nitrogen applications.

Important effort

The importance of nitrogen ap­­plication efficiency can’t be overstated, said Castellano. While nitrogen fertilizer is an important input for crop productivity, it’s also the costliest, so application at optimal levels is critical not only to the farmer but also for the environment.

“This is a serious challenge,” said Castellano. “We know we have water quality challenges we have to address.”

The average optimal nitrogen rate recommendations currently provided by ISU don’t necessarily consider other factors that contribute to variability such as seed selection, residue management or soil management. Even the weather has an impact.

Studying nitrogen application rates across Iowa’s landscape — from farm to farm and field to field — allows for more precise advice.

“If everybody applied the recommended rate from ISU right now …, roughly 20% to 30% would be underapplying nitrogen and 20% to 30% would be overapplying nitrogen,” Castellano explained. “The remaining would be right around the optimum. There’s huge variability in the actual optimum rate.

“If everybody moved to the right rate for their field and at the same time improved their efficiency, we would reduce environmental losses,” said Castellano. “That’s what the Iowa Nitrogen Initiative is studying.”

Precision agriculture advances have allowed for large-scale experiments across the state, utilizing data and computer science as well as machine learning, artificial intelligence and process modeling, all with the goal of determining optimal nitrogen rates in a given field and year.

“The goal of the Iowa Nitrogen Initiative is not to just provide more information to identify what the optimum nitrogen rate is, but also to manage toward higher efficiency,” Castellano said. “Fewer pounds of nitrogen per bushel of corn. Environmental outcomes really are an important piece of what we’re doing here.” 

2023 data

Early data from 90 of the 270 trials in 2023 noted some interesting trends, said Baum. All trials followed a timely planting — most from April 10-30.

“We have economic optimum nitrogen rates all over the spectrum,” Baum explained. “It’s in­credibly variable. There’s opportunity to save a lot of money in terms of passes through your field and nitrogen fertilizer costs.”

Economic optimum nitrogen rates ranged from 77 to 353 pounds per acre, with a 50% probability of the rate being lower than 200 pounds per acre and a 75% probability it was less than 240 pounds per acre.

Yields at the economic optimum nitrogen rate ranged from 130 to 287 bushels per acre; however, 90% of trials had a yield optimum nitrogen rate greater than 200 bushels per acre.

Easy to participate

Miller said participating in the trials is simple. Willing farmers commit to reserving a 5 to 10 acre plot of their farm for a personalized variable rate nitrogen prescription. 

All other farming decisions, including the nitrogen application for the rest of the field, remain with the farmer.

The Iowa Nitrogen Initiative will gather all necessary data, develop decision support tools and return information back to farmers about optimum nitrogen rates on their farms.

All data and identifying information remains private. 

“We’re only getting data from inside the trial,” she said, “not the rest of the farm. All that data comes without names or addresses at­tached. We’re creating separation be­tween names and the data because we care about your privacy.”

Interested farmers, certified crop advisors or custom fertilizer applicators can contact Miller for sign-up at or call 515-567-0607. More information can be found at

“The ultimate goal of all of this is to develop a web-based application that visualizes the data for you and helps you determine how the data that we’ve collected and what we’re learning impacts your operation,” Miller said. 

“We’ve taken a lot of steps toward that.”

Castellano said Iowa farmers consistently rank as the most efficient in the world. The project’s work will create improvements that “ensure Iowa farmers stay the most efficient with nitrogen fertilizer management,” he said.

IFBF hosts Iowa Nitrogen Initiative webinar Jan. 18

Iowa Farm Bureau will host a webinar at 1 p.m. Jan. 18 highlighting the Iowa Nitrogen Initiative with a focus on improving profitability. Speakers will include Dr. Michael Castellano, professor and lead of the Iowa Nitrogen Initiative and the William T. Frankenberger Professorship in Soil Science, and Melissa Miller, Iowa Nitrogen Initiative project director.

Webinar topics will include how to better understand and predict optimum nitrogen fertilizer rates across a field, thus boosting productivity and profitability while avoiding the environmental costs of excess application. Scan the QR code here to register.