It's Not Easy Being Yellow (Again!)

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

        Yellow corn is a typical sight around the Fond du Lac countryside this spring; however, not too many farmers are complaining because they know it's a better alternative than not having the crop even planted.  The reasons for corn being inflicted with this agronomic equivalent of jaundice can vary.  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 a more typical weather pattern returns (at least I hope it does).  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.  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.