What happens when Mother Nature doesn’t cooperate, and key spring jobs pile up? What if the calendar says you should plant corn, but you still have nitrogen to apply?
Two Midwest agronomists, Dan Quinn and Mark Licht, answer questions that might be on your mind in this situation. Quinn is the Purdue Extension corn specialist. Licht is an Extension cropping system specialist with Iowa State University.
If you think they will make the decision for you, think again. In fact, initially, each takes a different viewpoint, and both support it with sound logic.
It is early May, and we have no corn planted. We always put nitrogen on ahead of planting, and it’s not on yet either. As soon as it is dry enough, should we put on N or plant, and why?
Quinn: If you are limited by equipment and can’t sidedress or apply nitrogen in-season with a coulter-injected sidedress applicator or surface-dribble application with a sprayer, applying N ahead of planting is likely your best option. Preplant N application allows for the fertilizer to be incorporated, which reduces risk of foliar plant injury and N loss through volatilization. That’s particularly true compared to broadcasting urea or UAN during the season.
Applying prior to planting also ensures adequate N is available early, supporting early vigor and stand establishment. Additionally, applying starter with N at planting can further support early growth and potentially reduce the need for additional in-season applications.
Licht: At this point, getting corn planted is a priority, especially if planting looks to push past mid-May. If putting some N on with the planter is possible, apply 30 pounds per acre and plant simultaneously. Aim to apply the remaining N between V3 and V6 growth stages, if not earlier.
If it is a straight-up debate between planting first or applying nitrogen first, I’ve got to think planting timely is a higher priority to ensure high yield potential. However, N is very important for corn yield potential. If corn is planted with no N at or prior to planting, getting N applied needs to happen sooner than a normal sidedress timing. Consider applying as early as V1.
If we plant now, what is the best way to get N on afterward? We do not have equipment for sidedressing.
Quinn: One of the most effective in-season application methods is applying with a sprayer equipped with drop tubes or Y-drops to band UAN on the soil surface. You can apply either between rows or alongside the base of plants. This method places N closer to the root zone and reduces potential losses compared to broadcast applications.
If drop tubes or Y-drops are not available, broadcasting urea is an option. It carries a higher risk of foliar burn and N loss via volatilization. Include a urease inhibitor to reduce volatilization losses.
Another alternative is applying UAN with the postemergence herbicide application. Take care to avoid foliar injury. Keep rates within recommended guidelines, and review herbicide labels carefully to ensure compatibility and crop safety. If your planter is equipped for starter fertilizer applications, such as a 2-by-2 system, this can be a helpful way to supply part of the N needs at planting. However, you can’t supply the full N requirement without risking seedling injury.
If you have irrigation, fertigation with UAN later in the growing season is very effective. You can apply supplemental nitrogen while matching crop demand for N during key growth stages.
Licht: One option is broadcasting UAN or urea, ideally before emergence to avoid plant injury from high application rates. With a broadcast application, hope for a quarter- to half-inch rain to help get N below the soil surface.
Another option is looking to a neighbor or custom applicator. You would want them to make the sidedress application early, between V1 and V3. Ideally, this would be injected near corn rows.
If we put on N now as anhydrous, how long must we wait before planting? What if we don’t wait?
Quinn: There’s no exact number of days that you must wait, but waiting a few days can help reduce risk of seedling injury, especially under dry soil conditions or in coarse-textured soils. The biggest corn seedling injury risks come from planting too close to the ammonia band, especially a shallow band; planting into dry, wet or cloddy soils; experiencing poor sealing of the injection; or finally, if anhydrous winds up directly in future corn rows.
To reduce injury risk, inject anhydrous at 6 to 8 inches with a good seal. Use GPS to offset planter rows 4 to 6 inches from knife tracks, and apply anhydrous ammonia at an angle to planting direction. If you smell ammonia after beginning application, conditions may not be good. Consider adjusting or delaying application. Even if you delay, injury can still happen if placement and soil conditions aren’t managed properly.
Licht: The biggest risk of anhydrous ammonia ahead of planting is high potential for seed and root injury. In a wet spring, it is not so much how much rain is needed, but instead about getting N converted to stable forms.
You also want some dispersion from the initial application band. Waiting a couple of days to a week will help, but there will still be some injury. One way to minimize risk is using GPS and applying anhydrous ammonia parallel and offset from coming corn rows. If that is not possible, apply at an angle to eventual corn rows.