How Nitrogen Levels May Influence Corn Fertilizer Decisions In 2026
Understanding how much nitrogen remains in the soil after harvest is an important step in planning fertilizer decisions for the next crop year. A recent article titled Residual Soil Nitrogen from Crop Year 2025, How Might It Affect 2026 Nitrogen Needs highlights how leftover soil nitrogen could influence corn fertilizer needs in 2026.
The article was authored by Amy Cooper, Mitchell Baum, Sotirios Archontoulis, Mike Castellano, and Melissa Miller and published through Iowa State University Extension and Outreach as part of the Integrated Crop Management newsletter. Their work draws on research conducted through the Iowa Nitrogen Initiative, a collaboration between Iowa State University and Iowa farmers.
Researchers measured soil inorganic nitrogen including ammonium and nitrate in 34 farm trials after the 2025 harvest. On average, fields contained 22 pounds of nitrogen per acre in the top 12 inches of soil.
This amount was much higher than in 2024 and similar to levels seen in 2023. However, results varied widely across fields, showing that nitrogen carryover is not the same everywhere.
Two key factors explain why residual nitrogen was higher in 2025. First, warm and wet weather increased soil nitrogen mineralization, allowing more nitrogen to become available during the growing season. Second, fertilizer nitrogen rates were lower than in the previous year, meaning crops relied more on nitrogen released naturally from soil organic matter.
The findings also showed that fields with higher leftover nitrogen often require less fertilizer to reach the best economic yield. This relationship is built into the N FACT decision support tool, which combines soil test results with weather and crop data to guide fertilizer rates.
With nitrogen prices rising and farm margins under pressure, the researchers encourage producers to consider soil nitrate testing before the 2026 season. Tools such as the Late Spring Nitrate Test can help determine how much nitrogen is already available. Results can then be used within N FACT to fine tune fertilizer applications.
The authors also note that modern corn hybrids use nitrogen more efficiently than in the past. This means farmers can often achieve strong yields with less nitrogen per bushel. Careful testing and data-based decisions can help producers manage input costs while protecting productivity and the environment.
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