Late-Season Applications Can Help Curb Nitrogen Deficiencies
The good news is that late-season N applications can work. Ideally, it’s not as good as a mix of preplant and earlier postplant N, but it can salvage yield potential. Some co-ops have flown urea this summer on as a rescue treatment. Another development that’s making late-season N applications possible are high-clearance sprayers that can apply N as corn nears tasseling and beyond.
In dry years like 2012, though, late-season N applications did not work well without rainfall to incorporate it.
“The key is, you need rain afterward to get it in the root zone,” says Fabian Fernandez, a University of Minnesota Extension fertility specialist.
How It Can Work
A 2010 Purdue University study compared treatments that started out with an initial 24 pounds per acre of nitrogen (N) as starter fertilizer at planting.
At V7 or V15 growth stages, researchers applied 28% urea-ammonium nitrate at 0, 40, 80, 120, 160, and 200 pounds of actual N per acre.
At harvest, the V15 sidedressed plots yielded 100 bushels per acre more than the starter-only control, and just 13 bushels per acre less than the V7 sidedressed plots. The agronomic optimal N rates for the two side-dressed timings were similar, with 188 vs. 178 pounds of N per acre for V7 and V15, respectively.
It’s important to realize, though, these results may not occur when N deficiencies occur due to saturated soils and field ponding. Corn stands are often compromised under these conditions because of root damage keyed by excessive soil moisture. Previous recommendations from Purdue researchers suggest applying no more than 60 pounds of N per acre to severely N-deficient corn during the vegetative period.
For more detail from the Purdue studies, go to