All spring we've been discussing deficiencies on corn plants and trying to determine if they are to blame on the weather or something else. Below are few fields with some images as examples.
Field 1. Striping, but no compaction.
Field 1. From a distance, the field looks better.
Field 2: Striping on the leaves.
Field 1: Healthy Corn, Adequate Nutrients, No Compaction
This corn in Field 1 is at V7 and has striping that might indicate a deficiency in manganese or sulfur. There is no compaction and all nutrients should be in adequate supply, based on a recent soil test and fertilizers applied. A sidedress application of nitrogen occurred about a week before these photos. So a gentle rain and some sun will make this corn "jump" and the striping disappear. We refer to this kind of symptom as a "transient deficiency," meaning that the symptoms are related more to weather than anything else.
Field 2: Sidewall Compaction
Like Field 1, corn in Field 2 has striped leaves that indicate a nutrient deficiency. When the roots were examined, sidewall compaction was clearly evident. The sidewall compaction limits root growth which limits the plant's access to available nutrients.
Overcoming sidewall compaction is extremely difficult. Last year we saw several corn fields where the frequent rains loosened the sidewall and allowed roots to break through. Some people will be tempted to apply a foliar fertilizer to try to help the corn. A foliar fertilizer may make the leaves green for a few days, but the amount of nutrients in a foliar product will not be enough to sustain the plant throughout the season.
These are two examples that were relatively easy to determine. Many fields fit somewhere in the middle of these examples, where compaction may be less of an issue and a nutrient problem may be borderline.
Field 2. Sidewall compaction is evident.
Field 2. Roots fan out along the seed furrow.
Field 3. Striping, no compaction, but needs N.
Field 3. Shallow-planted but otherwise healthy.
In Field 3, the corn has some leaf striping. There is no indication of compaction and most nutrients are adequate. The farmer was going to sidedress N that day and that is probably all the corn plant needs. Some of the plants were shallow-planted and that could make the corn more prone to lodging late in the season. But the crop is otherwise healthy and the full amount of N should be applied.
Successfully determining if the deficiency symptoms are transient like in Field 1, or a result of compaction like in Field 2, or simply the need for a planned nitrogen application like in Field 3, will help you make the proper management decisions in your fields. Perhaps the most difficult thing to do is to leave a field alone, like in Field 1. Yet, in some fields, that is the best decision to make.