Many questions cross grower's minds regarding nitrogen application. Fabian Fernandez*, University of Illinois Extension specialist in soil fertility and plant nutrition, says those are difficult questions to answer generally. He says the most practical approach to determining whether additional nitrogen is needed is to perform strip nitrogen applications in a field to see if there is a response in growth or level of greenness due to nitrogen.
If additional nitrogen is needed, Fernandez offers a few reminders for growers to consider.
1. When should I apply nitrogen?
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.
*Note: Fabian Fernandez currently works for the University of Minnesota.