Excitement builds once tassels emerge in your corn crop. Nothing deflates that excitement faster than finding obvious signs of nitrogen deficiency. What if leaves below the ear leaf show classic deficiency symptoms? Can you rescue the crop by adding nitrogen now?
In 2011, Bob Nielsen and Jim Camberato, then both Purdue Extension agronomists, attempted to find out. They set up scenarios where plots were deficient in nitrogen on purpose when corn tasseled.
Their results demonstrated that corn could recover from significant N deficiency stress with applications of sidedress N fertilizer even as late as V13 to V15 leaf stages, Nielsen concluded. In a year when weather can delay fieldwork, options remain to recover significant yield with late sidedress N applications, he added. Practically speaking, that may be with a high-clearance sprayer and Y-drops or similar equipment.
Dan Quinn, current Purdue Extension corn specialist, and Mark Licht, Iowa State University Extension cropping specialist, tackle this real-life scenario:
Corn is tasseling and turning yellowish, with firing of bottom leaves. Nitrogen is determined to be deficient through tissue testing. Will it pay to apply more N now? If so, how much? How should it be applied? What form of N should be used?
Quinn: While the majority of a corn plant’s nitrogen uptake occurs before VT, there is still N demand through grain fill. If the crop shows good yield potential with a healthy stand, strong ear development, and weather is favorable, then a late-season N application may help maintain or even improve yields. That is especially true if you already observed N deficiency symptoms.
However, responses to N at this stage are often more variable. Potential benefit decreases quickly beyond VT. A rescue application of 30 to 60 pounds of N per acre is recommended here. Applying higher amounts is unlikely to be cost-effective, with the limited uptake window. The best application method here would be liquid nitrogen, either 28% or 32% N, applied using Y-drops or drop tubes. Place N between rows or next to rows while minimizing contact with foliage.
I would not recommend a broadcast urea application here due to the high potential for plant injury and foliar burn. In addition, foliar spray applications of N often do not provide any benefit because rates applied are too low to be beneficial.
Overall, a rescue N application at VT may be worthwhile if the crop has high yield potential. Use 30 to 60 pounds of N per acre in a banded application of UAN near the base of plants. This optimizes uptake and minimizes potential N losses.
Licht: At VT or tasseling, and for sure by R1 when silks are likely already viable, corn plants have taken up almost all the total N they anticipated receiving. A rescue application now has less ability to mitigate a nitrogen deficiency than if applied earlier. At this point, the plant has already made certain decisions about ear size.
Stress at or during pollination can reduce the number of final kernels which develop on each ear. Still, a rescue application of nitrogen may provide some nutrient stress relief.
The best approach is using high-clearance equipment with drop tubes or Y-drops. Apply UAN solution near plant roots. This timing would only benefit from 10 to 20 pounds of N per acre.