As we look at corn fields around the county, their growth is extremely variable (it's pretty much that way in any part of the state that I have been in).Some fields are uniform and green while others are uneven. Some of the corn fields with both conditions have some corn with yellow leaves. With the wet weather, many wonder how the nitrogen has survived de-nitrification. or leaching. The yellowing lower leaves are common in some fields and usually thought to be nitrogen deficiency. There may be more to it than that this year. There may be nitrogen deficiency, not due to the lack of it in the soil, but due to the plants inability to get the nitrogen out of the ground successfully. This may be due to poorly developed corn roots or subsurface moisture not being found. Nitrogen deficiency shows up as yellowing of the tips of the lower leaves. It progresses down the leaf towards the stem along the midrib. If there is not adequate nitrogen for whatever reason, the lower leaves are aborted and the nitrogen is shipped in the corn plant to the new growth. Producers have lived with nitrogen deficiencies in various years for a long time. Nitrogen stress can be true nitrogen deficiency (nitrogen washed away), a root problem, as mentioned above, or senescence of lower leaves (after tasseling). Thus identifying soil as truly nitrogen-deficient can be difficult. According to Dr. Mullen, Extension agronomist, to figure out if the symptom is a true soil nitrogen deficiency, a few nitrogen-rich strips should be used as a comparison. If there is a concern next season, apply a couple of reference strips to determine if nitrogen management is supplying enough nitrogen.Reference nitrogen-rich strips should have 25-30% more than the normal rate one applicator strip wide.This allows for side-by-side comparison if nitrogen is actually limiting.If clear differences are seen, additional nitrogen would be needed.If there is no difference, additional nitrogen would be of no value. Tissue testing for nitrogen deficiency still runs into the same pitfalls.There is still a question of whether the yellowing is a true soil nitrogen deficiency or a root system that is not developed properly and not allowing the plant to get the nitrogen out of the soil. Some other deficiencies that pop up from time to time would be worth covering this year as they can be easily confused with nitrogen deficiencies. Potassium deficiency can be confused with nitrogen stress. Both symptoms begin with yellow leaf tips at the lower leaves. The difference is that in a potassium deficiency, the yellowing occurs along the leaf margin toward the stem. Potassium is mobile like nitrogen, so it starts on the lower leaves. This is important to know because of other deficiencies' symptoms that produce yellow leaves. Soil testing can readily reveal a potassium soil deficiency. Phosphorous deficiency causes the leaf margin and lower leaves to turn a purple color.Corn plants deficient in phosphorus have a dark green color because leaf expansion is retarded more than chlorophyll and chloroplast formation.Soil testing reveals a phosphorus soil deficiency. Sulfur deficiency appears as a general yellowing of higher leaves. This is where some confuse a sulphur deficiency with a nitrogen deficiency, which starts on lower leaves. Sulphur does not easily move within the plant and younger leaves show the visual symptoms.Sandy soils with low organic matter are the most likely soil for this deficiency to show up. Magnesium-deficient plants show intervenal yellowing of lower leaves. Magnesium is mobile in the plant like nitrogen and potassium, so older leaves show symptoms first. Magnesium deficiency is not common. but acid sandy soils can be deficient. OSU Extension embraces human diversity and is committed to ensuring that all educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, age, gender identity or expression, disability, religion, sexual orientation, national origin, or veteran status.