Q: When should I consider an “in-crop” application of nitrogen?
A: Under the arid environment of the Canadian Prairies, splitting nitrogen applications in annual crops (e.g. applying 70 per cent of the nitrogen at time of seeding and top dressing the balance during the vegetative stage) rarely provides an agronomic benefit over applying all the required nitrogen up front. However, some situations do exist where an in-crop application of nitrogen may be worthwhile.
In springs where soil moisture reserves are in short supply, a reduction of nitrogen fertilizer may be a prudent move. However, if moisture conditions improve shortly after planting, additional nitrogen to match the improved yield potential can be a worthwhile effort. The key to success is to apply nitrogen as early as possible (preferably before mid-June) and have adequate rainfall shortly after application.
Yes, it is known to happen that a less than desired amount of nitrogen is inadvertently applied during seeding (i.e. operator or equipment error).This nitrogen shortfall can be made up with a timely in-crop application. While yields may not be 100 per cent recovered, compared to an upfront banded application, there is still a strong likelihood of an economic return.
In years where yield prospects are higher than expected (generally due to favourable moisture conditions), grain protein content is likely to be low. Some top-dressed nitrogen at the flag-leaf to early-filling stage in wheat can serve to build additional protein and hopefully reap the rewards of a protein premium.
The two primary products of choice for top dressing are urea and UAN (liquid 28-0-0). Both products are subject to gassing off losses, so if rainfall is not expected within a couple of days of application, a urease inhibitor should be considered. If utilizing UAN as the nitrogen source, it is strongly advised that it be applied as a stream as shown in the accompanying photo (see at top). A foliar treatment, such as would be achieved through a flat fan nozzle, can result in substantial crop burning and a yield loss.
Norm Flore, PAg, CCA, is a manager of agronomic services for Nutrien Ag Solutions in southern Alberta.