Peter Thomison, Ohio State Extension
Recent cloudy, cool, rainy weather has slowed growth of corn. Corn seedlings often turn yellow due to low nitrogen uptake and/or limited chlorophyll synthesis under cool, wet conditions. The visual appearance may be interpreted as N deficiency, but often this is not the case. Excessive water leads to poor respiration of the roots inhibiting nutrient uptake, or accumulation of nitrite (especially true on poorly-drained soils) in the soil which the plant takes up (nitrite is toxic to the plant).Yellowing of corn plants at this stage of development generally has little or no effect on later crop performance or yield potential. If it's induced by environmental conditions, the yellow color should change to a healthy green after a few sunny days with temperatures above 70 degrees F. The warm temperatures forecast this week should help in this regard.
If plants remain yellow, then closer inspection and assessment are needed to determine if yellowing is caused by nutrient deficiency or some other factors. Given our weather conditions this year, a nitrogen deficiency is most likely responsible for leaf yellowing.
In fields where extensive ponding has occurred, there may be significant loss of soil nitrate nitrogen due to denitrification or leaching. Differences in plant color will become pronounced as corn plants in the better drained areas around “wet holes” green up and begin to grow rapidly (especially post V6). In contrast, corn in the poorly drained areas will remain stunted and chlorotic. Corn in these wet holes usually benefits from sidedress nitrogen. Knifing in sidedress N fertilizer can also break up dense surface layers and promote better soil aeration.
Source : osu.edu