If you planted corn early and it's up and ready to go, you may be ready to apply sidedress nitrogen. More people seem to have taken advantage of the early spring to apply more pre-plant anhydrous than usual, but many seem to be starting a new practice- apply anhydrous on odd-shaped fields which are difficult to sidedress, but leave easy-to-sidedress fields where corn damage will be less for sidedressing,. The efficiency of sidedresing and getting nitrogen on closer to when the plant will need it still has appeal for many people.
Those who wait and sidedress would like to know how much they should apply. When first introduced many years ago, the pre-sidedress nitrogen test, developed at Iowa State University, seemed to hold promise as the answer to determine N rates when sidedresing. However in the decades since its' discovery, it's become apparent that it is at best a tool for tweaking rates. It's also best used where you've applied organic fertilizer, like hog manure. If you expect it to give you reliable results on mineral soils where you apply commercial fertilizer, you may find that the results aren't that meaningful, notes Jesse Grogan, an Indiana Certified Crop Adviser and agronomist with LG Seeds.
Grogan believes the test has several limitations. It works best when use d to pick up how much nitrogen may be released form organic matter, manure, or where new fields are brought into production after sod. That could apply to fields coming out of conservation reserve, assuming the cover there included some legumes that would produce N, and not just forage grasses.
The problem is that nitrate levels vary greatly depending on soil conditions in this part of the world, Grogan says. It's hard to interpret medium to low test readings from the test. This test certainly isn't the be-all. End-all answer to figuring out how much N to apply as sidedress for corn, he concludes.