Most of our customers use side dressing to split or spoon feed there corn crop. For example if they apply 150lb of nitrogen in the spring they now take part of that and apply 100lb in the spring and 50lb side dress later season V5 to VT (or what ever works for you). We will also fully apply all the nitrogen needs on the headlands during spring to make side dressing as fast and efficient as possible.
The crop needs little nitrogen during early vegetative stages to about the fifth leaf development stage. The largest portion of the total nitrogen taken up by corn occurs during the eighth leaf to VT (tasseling) development stages. Nitrogen uptake is mostly done shortly after pollination. Thus, applying N before the V8 development stage is best. Research has shown that if applications are done around V6, it is very rare to see yield loss due to N stress. This is because most soils in Illinois can provide sufficient N to satisfy the demands of young corn plants.
Of course, if a portion of the total nitrogen was applied preplant or at planting, a delay in application of supplemental nitrogen is not likely going to cause plant nitrogen stress. In cases where no nitrogen was applied, or the nitrogen supply is very low, make it a priority to apply early (preferably before V6) to avoid loss of yield potential.
The more you feed corn, the more it will feed you, so side-dressing (a second dose of fertilizer that boosts growth) is a must with corn.
Side-dress corn twice: when it's knee high and when it tassels. To side-dress, sprinkle a thin line of fertilizer or manure about four inches from the plants on both sides of each row of corn. To side-dress hill-planted corn, simply sprinkle fertilizer around each hill, about four inches away from the cornstalks. It often helps to make a shallow furrow first for either rows or hills. The furrow serves as a guide and the indentation helps the fertilizer stay put.
If you side-dress shortly before it rains, you're lucky. Otherwise, you should water, so the fertilizer leaches into the soil where it can be taken up by the corn roots