If you could pick a time to apply your nitrogen, would it be the seven-leaf stage, a fairly typical stage for sidedressing? Or would it be much later, at the 15-leaf stage, when you need special equipment to get across the field.
The answer is obvious- at the 7-leaf stage. But if mother nature rears her head again and cuts of certain field from being able to be sidedressed in a timely manner, there's still hope. Don't despair- just line up a late application instead.
That's based on work by Bob Nielsen and Jim Camberato of Purdue University, in a field study at the piney-Purdue farm near Wanatah last season. Their conclusion was that if corn gets by the normal sidedress state, it still pays to figure out how to get more N out there, rather than just taking a risk that you've got enough to produce a decent crop.
The yield topped 200 bushels per acre at more than 200 pounds of N applied, both for the sidedress, or leaf V7 stage, and was somewhat higher for the corn sidedressed at v& vs,. V15. However, the differences were not large. The was a large difference between applying the late N and not applying it at all.
The graph that says it best from the study is of kernels fertilized per ear vs. when N was applied. In all three cases, the number of ovules fertilized was less than the number of kernels produced. The biggest loss of ovules was in the corn that received only starter fertilizer. In fact, early sidedress produced 682 ovules, vs. 627 for late N application and 623 for starter only. If you stop there, you might wonder why go tot eh effort of applying N late.
The story doesn't end there. Kernels set were 550, 519 and 407, respectively, Kernel weight was 311 grams, 312 grams and 246 grams, respectively. Suddenly it's a different story.
The specialists used a coulter-injection tool are to make the late N applications. However, they note that if one is not available, you could still do the same thing using a high-clearance applicator with drop nozzles. There is minimal loss of N due to volatilization if the canopy is closed. By that time in the season, the canopy will be closed.