Late April /early May planted corn is now reaching the growth stage V-6 ( 6 fully developed leaves-canopy about 12-18 inches high) where the crop begins to take up significant amounts of Nitrogen(N) which is critical to reaching full yield potential. With N fertilizer prices rising, it is important to use N efficiently.
If your corn has had manure/compost applied or follows a forage legume crop, use of the Presidress Nitrogen Test (PSNT) could be helpful to determine if you have adequate N from those sources to reduce or eliminate the need to apply additional fertilizer N. This test may also be helpful to those who applied all their intended N prior to or at planting and had significant and repeated rainfall since planting. In some cases significant amounts of N may have leached and a supplemental N application may be warrented. Details and procedures on how to use the PSNT soil test can be found in a RCE Fact Sheet by Dr Joe Heckman. As noted in the fact sheet, the test can be used for other crops and the testing is available from the Rutgers Soil Testing Laboratory. Regardless of whether you need to test or not, if you are applying sidedress N be sure to get it on by stage V8 (8 fully developed leaves(2-3 additional leaves may be showing from the whorl)-about 18-24 inches tall).
Zane Helsel (adapted from Joe Heckman)