Apply nitrogen or plant corn?
The end of the optimal time for corn planting is quickly approaching. Getting corn planted should be a priority over making nitrogen (N) fertilizer applications. However, along with that decision there should be a plan to get N applications completed after planting and crop emergence. Switching products and application from preplant to sidedress requires availability of needed fertilizers and equipment. So have a plan in place.
Apply fertilizers if it does not delay planting
If planned fertilizer applications can be made without a delay in planting, then go ahead and make the applications. For materials such as urea or UAN solution (urea-ammonium nitrate 28 percent or 32 percent solution), those can be broadcast and incorporated with normal tillage before planting. This will work if applicators can stay ahead of tillage operations. Incorporate both of these fertilizers rather than leave them on the soil surface to avoid volatile N loss from the urea. If time is critical and application is to be made with pre-emerge herbicides, then surface application is an option, although more risky due to potential volatile loss and the applied N remaining on the soil surface (especially in no-till) if there is not sufficient rain to move it into the root zone. A rain (at least 0.25 to 0.50 inch within approximately two days after application) will eliminate volatile loss concern. Or, use a urease inhibitor to slow urea conversion, which provides more time for rainfall to move urea into the soil.
Anhydrous ammonia before planting
Anhydrous ammonia has some additional considerations. It must be injected, and the ammonia band will initially have high pH and considerable free ammonia, which can burn corn seedlings and roots. There is no exact “safe” waiting period before planting, and injury can happen even if planting is delayed for a considerable time period. The risk of ammonia injury depends on many factors, with several that are not controllable. For example, risk increases if application is made when soils are wet and then dry (ammonia moving up the injection track); with higher application rates; when soils with high clay content are wet (sidewall smearing of the injection track and ammonia moving toward the soil surface during application); and when soils are very dry and coarse textured (larger ammonia band). At the current time with the wet soils, the first risk is more likely and it is not uncommon for damage to be found later in the spring. A few things can reduce the risk of ammonia damage: wait and apply when soil conditions are good; have a deep injection depth (seven or more inches); wait several days until planting; if the injection placement relative to future corn rows can’t be controlled, apply at an angle; if the injection placement can be controlled with GPS guidance positioning technology, split future corn rows – with this system no waiting period is needed.