ISSUE 9   June 29, 2006


Several calls have come in this summer regarding stunted and severely purple corn. One of the reasons I am not terribly excited about "deficiency symptoms" is that if the nutrient is really deficient, the crop will assume a certain color or symptom. However, there are often environmental or soil conditions that might also result in the same crop appearance. In the case of purple corn, it can be an indication that the crop is phosphorus (P) deficient. If the crop is truly P-deficient, it will turn purple. However, there are a number of other environmental factors and soil conditions that can result in the same appearance. These factors include soil compaction, variety tendency towards purpling, acid soil, cold soil, and a poor root system.

Of the calls taken this spring, two stand out as unusual. The first was regarding a field where purpling was occurred in corn seeded over an old shelterbelt taken out a few years ago. The topsoil had been disturbed and it is likely that the P levels in the old buried shelterbelts are much lower than the rest of the field. Although the whole field was soil sampled, a composite sample of the field probably masked any low P that might exist in the shelterbelt areas.

The second unusual call was about a field that had been seeded to corn directly over anhydrous ammonia bands applied just a few days prior to planting. It is likely that the root system was restricted by the ammonia band and was not able to feed the plant normally. Corn roots usually feed from the edges of the ammonia band until the ammonia is transformed to nitrates. This can take 2 to 3 weeks under our typical May-early June conditions. Basically, anything that restricts the rooting of corn can result in purpling. Some varieties are much more prone to purpling than others. If you encounter what looks like "text book" nutrient deficiencies, donít rule out other possibilities as a primary problem, with the deficiency symptom as a secondary concern.

Dr. Dave Franzen
NDSU Extension Soil Specialist

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