Nitrogen deficient corn, what’s the cause?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

This summer I received calls from several farmers indicating that they were seeing signs of N deficiency on the lower leaves of corn, even though they had applied what should have been adequate nitrogen. Some of these situations involved the application of partially composted dried poultry manure. In some cases similar N management programs were being used on adjacent fields or different fields of a farm. In some fields the corn was growing well, but in other fields with a similar N program the corn was “firing” or showing signs of N deficiency. I also observed a lot of fields showing “firing” of the bottom leaves. Why did this happen? The answer to this question may be associated with the weather and rainfall pattern this year. This problem appears to have been worse on sandy soils with lower moisture holding capacity.

Two factors may contribute to this problem. During the first part of the growing season soil moisture was generally more than adequate, but as we moved into mid-July and August many areas of the state become dry and drier. With good early soil moisture corn roots may have developed predominantly in the surface soil. When the soil became dry the corn root system was not able to supply adequate moisture to the plant. Much of the nitrogen is moved to the root in the water moving to and taken up by the root. Therefore, less water supply means less nitrogen supply.

Secondly, when soil becomes dry, microbial activity decreases and less N is mineralized from soil organic matter or organic materials, such as compost, biosolids, animal manures or legume cover crops that are added to the soil. Therefore, even though adequate N was applied in one of these materials less N was mineralized for crop use than was expected. Therefore, soil moisture can have a significant effect on N availability and uptake. Even though some fields may appear to be similar, slight differences in clay or sand content can make a difference in moisture supply. Soil compaction can also accentuate this problem by limiting root development and moisture supply. Managing soils to improve soil organic matter over time will improve soil quality and moisture holding capacity

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