Consider water monitoring to fine-tune your nitrogen strategy

May 29, 2025 | Kriss Nelson

Water monitoring efforts are underway across Iowa, and early results are raising questions. Spring nitrate levels have been higher than anticipated, according to Tony Seeman, Iowa Soybean Association (ISA) water lab service manager.

“Between spring rains and warmer temperatures, we’re asking: Did the nitrogen mineralize more than expected? Was it the weather? Or maybe there was more residual nitrogen in the soil than we thought,” Seeman says.

Regardless of the cause, elevated nitrate levels in water represent lost nutrients and lost dollars.

Early season results

Samples collected in April from tributaries in the Middle Cedar River watershed were the highest nitrate levels measured since monitoring began in 2017.

In areas where monitoring has been ongoing for a longer period, such as the Raccoon and Boone Rivers, results are similar last April.

While there have been pockets of moderate drought, soil moisture conditions showed improvement coming into this year.

“The main question at this point is whether this represents a shift with an earlier peak than usual, or whether nitrate levels will continue to rise even higher through June,” says Seeman.

What can farmers do?

Farmers are encouraged to factor nitrogen monitoring into their nutrient management plans. Tools like Iowa State University’s (ISU) Nitrogen Fertilizer Application Tool Iowa State University’s Nitrogen Fertilizer Application tool (N-Fact) help estimate how much nitrogen remains in the soil and guide future application rates.

“Maybe some fields didn’t get planted as early as you had hoped, or you have gotten more or less rain than usual,” says ISA Senior Research Agronomist Alex Schaffer. “The N-FACT tool accounts for these environmental factors and local multi-rate nitrogen trials to recommend the economic optimum nitrogen rate to apply to a field.”

Another tool farmers can use is ISU’s Late-Spring Soil Nitrate Test. Schaffer says this test evaluates available nitrogen before the corn crop begins rapid uptake.

“This test can give a very definitive answer whether a sidedress application of nitrogen is necessary or not,” he says.

Download the free Late-Spring Soil Nitrate Test info here.

Start monitoring now

Seeman encourages farmers to begin water monitoring as soon as possible to improve nitrogen use efficiency.

“You will not learn everything in one year,” he says. “But the sooner you collect data, the more powerful your decision-making becomes.”

For more information or to get started, contact Tony Seeman at aseeman@iasoybeans.com.

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