It's Not Easy Being Yellow

Mike Rankin
Crops and Soils Agent - Fond du Lac County
University of Wisconsin - Extension

        Many area corn fields that looked postcard perfect last week have changed course and taken on a yellow appearance that can only be characterized as a ton of ugly. Although many corn fields have been inflicted with this agronomic equivalent of jaundice, the reasons are likely varied. The first cause that comes to mind is nitrogen deficiency. Where soils have remained ponded or saturated for several days (if not weeks), nitrogen loss in the form of denitrification has likely occurred. In some cases, the saturated soils have slowed conversion of organic forms of nitrogen (manure and legumes) into a form that that the plant can readily utilize.

I suspect that the long stretch of wet weather has really taken a toll on corn root systems. Saturated and compacted soils are typically oxygen deficient and retard root growth. This results in decreased nutrient uptake and top growth that may be every color but green.

A final reason for ugly corn is the fact that many fields have had to be sprayed with herbicide while the corn is in a stressed condition. Metabolism of the herbicide is slower than normal and the corn plant reacts accordingly.

Short of spray paint, how do I correct the yellow corn problem?

        The good news is that many fields will "grow out" of their current ugly condition as more typical weather patterns return. If corn is not too tall, cultivation will accelerate this recovery by aerating soils. This will have the multiple impact of enhancing root growth, nutrient uptake, and the mineralization of organic nitrogen to a plant available form. We’ve seen it occur before, and it will happen again in 1999. The exception to this recovery model will be situations where there is simply not enough nitrogen available to the crop because of loss or inadequate amounts applied. In these situations, additional nitrogen will need to be applied as weather and crop conditions allow. Corn will respond to added nitrogen up to tasseling. Where corn is too big to inject nitrogen into the soil, broadcasting or applying urea with drop tubes may be viable options.

For more information contact Mike Rankin