Corn roots may be suffering, if planted in damp soils that became compacted then crusted with beating rains. University of Illinois Extension crop specialist Emerson Nafziger says cultivation could break up the crust and mulch the soil to retard evaporation, and give oxygen to the roots. Corn with yellow leaves is not photosynthesizing well and is standing in water. He says its roots will not recover very fast due to slow soil drying.
If your corn is yellow, it is likely due to wet soils and depleted nitrogen, and there is little that can be done until the soils dry out, Nafziger says. The quick warm up helped the leaves at the expense of the roots, and their demand for moisture and nutrients outstripped the ability of the roots to supply the needs. He says the roots need oxygen, and need to escape from carbon dioxide. Nitrogen will only enhance vegetative growth, which will not help the roots. Nafziger says the roots need to grow without your help.