Navigating Nitrogen Management in Wet Spring Conditions – Does the corn need more nitrogen?

This is part three of a three-part series on nitrogen management this spring. Read part one “Navigating Nitrogen Management in Wet Spring Conditions – Nitrogen Loss Mechanisms” and part two “Navigating Nitrogen Management in Wet Spring Conditions – Estimating Nitrogen Losses.”

Do I need to apply additional nitrogen?

It's the million-dollar question, and given the wet spring we've had in Iowa, many farmers who applied N last fall or early this spring find themselves asking it. It's a valid concern given how essential N is for optimal corn production. Unfortunately, right now, the only thing that I, or any other nutrient management specialist in the Midwest, can say with any conviction is that mid-May is not the optimal time to decide on increasing N rates for your corn. Research shows corn N recovery during early growth does not necessarily correlate with yield. Those with early planted corn may notice some light-green areas, which could suggest N deficiency but may also be due to saturated soils slowing root activity and growth. At this point, we must also evaluate stand damage, replant requirements, and other yield-influencing factors before deciding on supplemental N applications.

So, when is the right time to assess nitrogen needs? The key lies in monitoring crop progress and soil conditions as the season unfolds. Factors like soil moisture and temperature will help determine the need for supplemental N. A good rule of thumb is to observe the color and growth of the corn by early to mid-June. As evidenced earlier in part two of this article series, many methods for determining supplemental N requirements use June as a critical period for decision-making. Soil moisture normalizing with sustained warm temperatures will favor crop growth and soil N mineralization, potentially offsetting the need for additional N. Additional N is likely not needed if the corn has good color and is growing well by early to mid-June. However, if wet conditions persist, restricting root growth and limiting crop access to soil nitrogen, or if the corn remains pale or stunted in early to mid-June even after the soils have returned to optimal conditions, a supplemental N application may be necessary. In this case, consider one of the techniques mentioned in part two of this series to help determine supplemental N rates.

Various methods are available for making supplemental N applications, each with unique considerations. Sidedressing of supplemental N can start immediately after planting. Below is a list of sidedressing options in order of most to least preferred:

1. Injected anhydrous ammonia, UAN, or urea:
   • This method places the N in the soil near the roots, reducing risk to young crops and minimizing potential N losses. Injections can occur in every row middle or every other row middle with the same efficacy. If injecting, ensure that the corn rows are visible or GPS guidance is used and that soil moved during application does not cover emerging corn plants.
2. Broadcast granulated ammonium nitrate or ammonium sulfate:
   • Be aware that this can cause leaf spotting or edge browning where granules fall into the whorl. The chance of damage increases with larger corn and higher application rates.
3. Surface applied urease inhibitor treated urea or UAN:
   • The urease inhibitor will help limit N losses via volatilization. Be aware that leaf burn and reduced early growth can occur with any broadcast urea or UAN application. The risk increases as corn plants mature past the three-leaf stage and N rates increase beyond 60 lbs N ac^-1.
4. Surface dribble UAN solution:
   • Try to plan applications before a rainfall event to help move the N into the soil and prevent losses via volatilization.
5. Broadcast urea:
   • Try to plan applications before a rainfall event to help move the N into the soil and prevent losses via volatilization.
6. Broadcast UAN:
   • Broadcasted UAN can be applied using common equipment (sprayer) and used as an herbicide carrier before corn emergence. However, read herbicide labels carefully, as most prohibit application in N solutions after corn emergence. There is a risk for N loss via volatilization unless rainfall occurs shortly after applying to move the N into the soil.

If preplant or early sidedress N applications were missed or insufficient, research in Iowa indicates that corn can benefit from mid-to-late vegetative stage N applications if there's a deficiency, though yield potential may be reduced. The chance for reduced yield potential is most significant when severe N stress is present, and soil conditions remain dry following application. Optimal results are achieved when applications occur before sufficient rainfall to move N into the root zone. If corn gets too tall for standard sidedress equipment, high-clearance equipment can be used to apply N by dribbling or injecting UAN or broadcasting urea.

Conclusion:

Managing nitrogen (N) in Iowa's wet spring conditions requires a deep understanding of nitrogen loss mechanisms and careful estimation techniques. Leaching and denitrification, driven by soil saturation and temperature, are key processes that farmers must account for to prevent significant N losses. By utilizing approaches such as spring rainfall triggers and the Late-Spring Soil Nitrate Test, farmers can make informed decisions about supplemental N applications. Ultimately, monitoring crop progress and soil conditions into early June remains crucial to determine the necessity and timing of additional nitrogen for optimal corn production.

This was part three of a three-part series on nitrogen management this spring. Read part one “Navigating Nitrogen Management in Wet Spring Conditions – Nitrogen Loss Mechanisms” and part two “Navigating Nitrogen Management in Wet Spring Conditions – Estimating Nitrogen Losses.”

References:

Bechman, T.J., 2024. “Determine how much nitrogen is left.” Indiana Prairie Farmer, May 6, 2024. https://www.farmprogress.com/corn/determine-how-much-nitrogen-is-left

Fontes, G., and Nafziger, E., 2024. "Wet Spring Weather and Nitrogen Loss Revisited." Department of Crop Sciences, University of Illinois at Urbana-Champaign, May 9, 2024. https://farmdoc.illinois.edu/field-crop-production/wet-spring-weather-an...

Sawyer, J., 2018. “A Late Spring- Nitrogen Considerations.” Iowa State University Extension and Outreach Integrated Crop Management News, April 17, 2018. https://crops.extension.iastate.edu/cropnews/2018/04/late-spring-nitroge...