Fertilizer sales rose in 2024, but researchers say farmers are getting more efficient

Iowa farmers purchased 5.4 million metric tons of fertilizer in 2024, an 11 percent increase compared to the previous year, marking the highest sales in a decade.

Although total sales of fertilizer are up by tonnage — by about 17.4 percent between 2014 and 2024 — experts say fertilizer usage has been fairly stable over the past few decades. And it’s gotten more efficient, especially when to the increase in yields.

“We're just becoming a bit more efficient as time goes on,” said Chad Hart, an Iowa State University economics professor and crop market specialist.

Hart said there are several factors playing into this, including advancements in seed technology and farmers shifting how they handle fertilizer and being cognizant not to over fertilize.

“The more nitrogen or more you fertilize, the higher the potential yield is,” he said. “But there is a plateau point out there where, nope, you're doing that, and once you exceed that point, then you can put all the fertilizer you want out there, and it's actually going to hurt yields, as opposed to help yields.”

Hart said farmers have gotten much better at not hitting that plateau over the past few years, in part because of when they apply the fertilizer.

“You'll see some farmers will fertilize in the fall, while others are fertilizing in the spring. You see some side dressing as the crop is growing,” he said. “They're trying to make sure that nitrogen is available to the crop when it needs it, so we are become much better at that.”

During the 2024 crop year, farmers applied more fertilizer to field in the fall than in the spring. About 3.1 million metric tons were used between July and December, while 2.3 million metric tons were used between January and June.

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Michael Castellano, a professor of agronomy at ISU, said that although the rate of fertilizer sales is going up, the efficiency of production is increasing.

“When we harvest more corn per acre, we need more nitrogen per acre to grow the crop,” Castellano said. “Yet, farmers are applying less nitrogen fertilizer per bushel production than ever before.”

Historically, Castellano said ISU recommended that producers use about 1.2 pounds of nitrogen fertilizer per bushel of corn. Later the recommended amount was reduced to 1 pound per bushel.

“This is why we need — and Iowa emphasizes — the importance of cover crops and edge-of-field water quality infrastructure investments such as denitrification wetlands, which are excellent at removing nitrate and add biodiversity to the landscape,” Castellano said.

John Gilbert, who has been farming in Hardin County since 1979, aims to produce more moderate yields to minimize the cost of inputs like fertilizer.

“We can have a target yield, and it may not be the maximum possible yield, but we feel it's a good target yield,” he said.

Gilbert said there likely are a number of reasons why fertilizer sales jumped more than 10 percent last year, but he speculated one factor may be the heavy rain much of the state experienced in the spring, which resulted in fertilizer runoff.

According to the Iowa Department of Agriculture, 2024 was the 29th wettest year on record.

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More corn often means more fertilizer

Hart said farmers are planting more corn than they did the previous year, which can lead to more fertilizer sales.

“This year, we did see corn acreage here in the state of Iowa going up fairly significantly,” Hart said. “But there's a compounding impact on that as well. Some of that acreage is an increase on what we call “corn-on-corn" area, meaning that this was land that was planted to corn last year, and it's going to be planted to corn as well this year.”

When farmers plant corn two years in a row, they often have to increase the amount of fertilizer they use to maintain the crop yield they are targeting.

“When you put those two things together that can help explain a lot of the growth in fertilizer we saw this year,” he said.

According to statistics from the U.S. Department of Agriculture, Iowa farmers planned to plant about 13.5 million acres of corn in 2025, an increase of 600,000 acres from 2024.

That increase is being seen at the national level as well. The study estimated that U.S. farmers will plant about 95.3 million acres of corn in 2025, up about 5 percent from the year before.

Why are farmers planting more corn?

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It’s “being driven by relatively better markets for corn than for soybeans due to a variety of issues,” Hart said. “Some of them are trade related, where corn exports have been going at a stronger pace than soybean exports. Corn markets (are) a little less volatile when it comes to things like tariffs and trade disruptions, and so that made it a little safer, if you will, place for farmers to move their crop.”

With more corn in the ground, Hart said it makes sense that fertilizer sales were up in 2024, because between corn and soybeans, corn depends more on having additional nutrients provided by fertilizer to grow the crop.

When it comes to if Iowa farmers are using too much fertilizer, Hart said he’ll argue that “too much is in the eye of the beholder.”

“If we can look at what the plants can actually uptake then the answer would have to be yes,” Hart said. “We do know that we do have nutrient runoff at the same time too. Farmers don't know exactly how much they need to apply in any given year because of the vagaries of weather and the way the crop develops. So, when you're applying, you definitely don't want to come up short.”

Hart said that if a farmer were to miss the recommended amount of fertilizer, farmers would rather apply too much as opposed to not enough to ensure the crop has the nutrients it needs to grow.

However, Castellano said according to a survey by Iowa Nutrient Research & Education Council that looked at fertilizer data, Iowa farmers applied an average 172 pounds of fertilizer per acre, which researchers determined was less than the optimum rate that year.

“It’s really tough from a year or two of data to determine if farmers are over-applying, but the answer looks to be on average, ‘no,’” Castellano said in an email to The Gazette. “If we think about how efficiency has changed over time, farmers are unquestionably becoming more efficient (with) less nitrogen applied per bushel harvested.”

Mitchell Baum, a postdoctoral research associate at ISU, said the university’s research can’t say for certain whether farmers are over or under applying fertilizer.

“Last year alone, we observed the optimum nitrogen rate to vary by almost 200 pounds across fields in Iowa. Because of this variability, there is undoubtedly fields that either don't get enough nitrogen and vice versa,” Baum said.

Baum said the university is working to create more region-specific recommendations so Iowa farmers can make informed decisions about their nitrogen management plans.

“With that said, we did find that the statewide average optimum nitrogen rate was 15 percent higher in 2024 than 2023, likely due to weather differences,” he said.

Additionally, Castellano said that the price of nitrogen fertilizer was “much higher” in 2023 than in 2024, which he said also could be a contributing factor.

Study: Optimal fertilizer rates have been increasing for years

In March, Iowa State University published a study that found optimal nitrogen fertilizer rates in the Corn Belt have been climbing for decades.

Iowa State University researchers found that the amount of nitrogen fertilizer needed to maximize corn production profits has been increasing roughly 1.2 percent per year for the last three decades.

The study tracked nitrogen fertilizer usage in the Corn Belt — which includes Iowa, Indiana, Illinois, Missouri, Nebraska and eastern Kansas — showing an increase of 2.7 kilograms of nitrogen per year. More nitrogen fertilizer is needed to reach optimal levels because nitrogen is naturally lost when its nutrients are absorbed into the growing plant and can be depleted when soil becomes eroded.

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“As much of a surprise as it was to us, it really wasn’t a surprise when you sat down and thought about it,” Castellano, who co-authored the study, said in the university’s news release about the research. “It’s like a bank account. If you pull money out, you need to deposit more money to keep the account going.”

Baum, who also participated in the study, said he analyzed a dataset tracking the changes in nitrogen rates over time to better understand what the optimum rates are.

By looking at the datasets, Baum found that the optimum rates were rising over time, which he said was “a novel thing.”

From there, the team of researchers studied small plots of land owned and managed by the university, to estimate optimal nitrogen rates, which is not possible with sales or survey data alone.

“The word optimum is the key here and is really, really important,” said Sotirios Archontoulis, who is a professor of integrated cropping systems in the Agronomy Department at ISU. “Across the 14 experimental sites, we also found that it is quite variable. It varies a lot from location to location.”

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“One thing about this study, as well as many other studies, will focus on the downsides of over application. This study also highlights the trade-offs of under-application and how that really harms yields and food production while also not having the environmental benefits you would expect to just reduce nitrogen fertilizer,” Baum said. “It really highlights the importance of applying at the optimum, not over or under amount. It really is kind of the sweet spot that maximizes yield while still sustaining good ecosystem services.”

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

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Comments: olivia.cohen@thegazette.com