Heavy spring rainfall across Indiana is prompting corn growers to reevaluate nitrogen management plans, particularly in fields where all nitrogen was applied at planting.
Members of the Indiana Certified Crop Adviser panel said rescue nitrogen applications may be warranted in some situations, but growers should first assess the likelihood and severity of nitrogen loss before making additional applications.
According to the panel, nitrogen loss depends on several factors, including soil type, fertilizer source, timing of rainfall, soil saturation duration and use of stabilizers. The primary mechanisms of nitrogen loss include ammonia volatilization, nitrate leaching and denitrification in saturated soils.
Purdue Extension senior research associate Betsy Bower said nitrogen losses are generally more concerning several weeks after planting, particularly in excessively drained or poorly drained soils where unstabilized nitrogen was applied. She noted that anhydrous ammonia typically has lower loss potential than urea or UAN solutions.
Bower recommended soil nitrogen testing to help determine whether additional nitrogen is needed. Sampling multiple 12-inch soil cores can help growers estimate nitrogen concentrations and assess potential deficiencies based on crop growth stage.
Several application methods are available for rescue nitrogen treatments. Bower said Y-drop systems can effectively place nitrogen near the corn row, although rainfall is still needed to move the nutrient into the soil. She added that drop nozzles on sprayers may also be effective when Y-drop equipment is unavailable. In taller corn, aerial urea applications may be an option.
Abby Horlacher of Nickel Plate Consulting said heavy rainfall and stalled crop growth have complicated nitrogen management decisions this season. She recommended using the pre-sidedress nitrate test to evaluate nitrogen availability. Sampling at least three representative field areas can provide a more accurate picture of overall conditions.
Horlacher also emphasized the importance of evaluating available application equipment and local retailer capabilities when planning supplemental nitrogen treatments.
Brian Mitchem of Farmer 1st Agronomy Consulting Services said saturated soils can rapidly lose nitrate nitrogen, especially under warm conditions. He noted that warm, waterlogged soils may lose 4% to 5% of nitrate each day saturation persists.
Mitchem explained that urea converts to nitrate within 10 to 20 days, while anhydrous ammonia conversion can take three to eight weeks. He advised growers to estimate potential nitrogen loss and evaluate corn for deficiency symptoms before deciding on a rescue application.
Symptoms of nitrogen deficiency include yellowing lower leaves beginning near the center of the leaf and progressing outward. Mitchem also recommended collecting tissue samples from multiple areas of a field for laboratory analysis, noting that ear leaf tissue samples provide the most accurate readings.
For in-season rescue applications, Mitchem said high-clearance sprayers equipped with Y-drop systems have performed well. Typical application rates are about 15 gallons per acre of solution.
Purdue Extension corn specialist Dan Quinn said growers should assess field conditions, crop appearance and estimated nitrogen loss before making supplemental applications. Soil type, fertilizer source, inhibitor use, soil temperatures and saturation duration all influence nitrogen availability.
Quinn said denitrification is more common in saturated, poorly drained soils, while leaching is more common in sandy soils where nitrate can move below the root zone.
He added that rescue nitrogen applications made before or shortly after pollination can help preserve yield potential when significant nitrogen loss is suspected. Quinn recommended liquid nitrogen applications delivered with high-clearance equipment using Y-drops or drop tubes to minimize crop injury. In many Indiana environments, supplemental applications of 40 to 60 pounds of nitrogen per acre are often sufficient to protect yield potential.
Source: Indiana Certified Crop Advisor Program, "Heavy rains? Assess nitrogen loss in corn"