What are N application options in a compressed spring?
It was a long winter, with conditions this spring suitable for field work perhaps being later than normal. Also, some areas of Iowa did not have the typical amount of fall anhydrous ammonia applied. Questions are already coming about options for nitrogen (N) fertilization this spring, and the usual question should time be taken to get N applied or plant corn and apply N later.
Urea, urea-ammonium nitrate solution, and other materials
If planned fertilizer applications can be made without a delay in planting, then go ahead and make the applications. Materials such as urea or UAN solution (urea-ammonium nitrate 28 percent or 32 percent solution) or polymer coated urea can be broadcast and incorporated with normal tillage before planting. Incorporate rather than leaving the fertilizer on the soil surface to avoid volatile N loss from dry urea or urea in UAN. If time is critical and UAN application is to be made with preemerge 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 rainfall of 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. Preplant or preemerge applications can be part of a split-N or weed-and-feed system, with a rate to supply part of the total N application need and the remainder applied sidedress.
Another fertilizer option is polymer coated urea, designed to delay urea release until soils warm. To avoid runoff loss, incorporate into the soil. Surface broadcast options, especially fertilizers for no-tillage that generally do not have volatile loss concern, are ammonium nitrate and ammonium sulfate. These products are not used extensively in Iowa as a primary N material, so would likely have limited availability. If disturbing soil is a concern in no-tillage from injecting N, then broadcast application is an advantage but also has the disadvantage of potential losses or immobilization of N with surface residue.
Anhydrous ammonia before planting
Anhydrous ammonia has certain 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). A few things can reduce the risk of ammonia damage: wait and apply when soil conditions are good; have a deep injection depth (6 to 7 inches or more); 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 track can be controlled with GPS guidance positioning technology, then split future corn rows – with this guided system no waiting period is needed. Anhydrous ammonia nitrifies more slowly than products like urea or UAN solution, so is a preferable N fertilizer for soils with greater potential for losses in wet conditions.