A field’s nitrogen needs vary from year to year. In a recent University of Nebraska Extension Crop Watch article, extension specialists explained that this need is partially dependent on the previous year’s weather conditions, previous crop nitrogen uptake and yield, and postharvest residual soil nitrogen.

The authors shared that when a growing season is drier than normal, it may limit downward movement of nitrogen (N) in the soil profile, nitrate leaching loss, crop nitrogen uptake, and crop yield. A reduction in yield could leave more residual N in the soil; a soil sample taken at a depth of 2 to 3 feet in the fall or spring would confirm this.

Timing of N application is critical for crop yield, N use efficiency, economic return, and N losses into the environment. Since precipitation is unpredictable, the potential for N loss is present during the fall, winter, and early spring. For this reason, the authors said that spring soil sampling and split N application (preplanting and in-season) is the best strategy. However, if applying N in the fall, consider the following practices to avoid over application and N loss.

  1. Sample soil at 2 or 3 feet deep to determine residual nitrate-N to be credited in nitrogen rate calculations.
  2. Apply fertilizer N or manure when soil temperature is below 50°F at a 4-inch soil depth.
  3. Apply anhydrous ammonia instead of other N fertilizers.
  4. Limit fall application of N to silt loams, silty clay loams, and finer textured soils.
  5. Avoid fall application on wet or flood-prone soils.
  6. Consider applying part of the N in the fall and the remainder during the growing season.
  7. Following University of Nebraska-Lincoln recommendations, plan to apply 5% more fertilizer-N in the fall compared to spring application to compensate for potential losses.

This article appeared in the November 2020 issue of Journal of Nutrient Management on page 9.

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