Key Considerations For Rescue N Applications

Rescue nitrogen (N) applications to corn may be needed when wet conditions prevent N applications or when the loss of applied N is suspected due to wet conditions. However, crop injury when N is broadcast applied may counteract the yield benefits of a rescue N application.

A group of researchers from the University of Missouri determined the effect of corn height, N placement, and source on injury and yield response. The group evaluated five site-years of research of the impact of broadcast and between-row placement of NH4NO3 (AN), urea-NH4NO3 (UAN), urea, and urea plus N-(n-butyl) thiophosphoric triamide (NBPT), a urease inhibitor, at 170 kg N hectare (about 150 lb/acre) either pre-plant or when the corn was 30, 60, 90, or 120 cm tall.

The visual injury for broadcast-applied N sources was then ranked with urea = urea plus NBPT < AN ≤ UAN 7 days after treatment.

The researchers found that injury was dependent on plant height. Leaf injury resulted in reduced yield when UAN or AN was broadcast on corn that was 60, 90, or 120 cm tall.

Broadcast urea or urea plus NBPT caused minimal crop injury and effectively supplied N to the corn crop. Application of NBPT-treated urea increased yield 260 kg hectare (229 lb/acre) averaged across timings when compared with urea alone. Application when corn was 30 cm tall produced the highest yields, but excellent yield response to rescue N was obtained at all application heights.

The optimal application height for N fertilizer was at about 30-cm plant height, regardless of placement (averaged across site-years and N sources). Grain yields were similar for broadcast and between row N placement when applied pre-plant or to 30- or 60-cm-tall corn. Yields decreased slightly, however, with BR applications and steeply with broadcast applications when applied to taller corn.

Finally, overall, the researchers believe that that the placement and source of N should be considered when rescue N applications are made to corn that is greater than 30 cm tall.

Summary adapted from:

Rescue Nitrogen Applications for Corn
Kelly A. Nelson, Peter C. Scharf, William E. Stevens and Bruce A. Burdick
Soil Science Society of America Journal 2011 75: 1: 143-151
doi:10.2136/sssaj2009.0456

(Source: Certified Crop Adviser)

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