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Nitrogen (N) fertilization for this year’s Iowa corn crop has been complicated by frequent and sometimes excessive rainfall from late last fall through this spring. Many farmers who normally apply N in the fall couldn’t, and spring preplant N application and corn planting has been challenging in many areas with the wet and extended cold soil conditions. Therefore, many farmers are uncertain about the N availability for corn, early post-emergence assessment of soil N supply, and the potential for supplemental sidedress N application.

Interest in monitoring and applying nitrogen (N) to corn at mid- to late-vegetative growth stages has gained interest in recent years due to wet spring conditions and equipment available to move through tall corn. Also, some farmers and crop advisers have been monitoring soil nitrate-N concentrations throughout the growing season. The question that has come up is what do soil nitrate-N concentrations mean when sampled at mid- to late-vegetative growth stages?