Top-dressing nitrogen (N) is on the rise across Western Canada for a number of reasons. Farmers are constantly trying to attain higher yields, and applying N after the crop has emerged allows a farmer to put down what he couldn’t with his seeder and manipulate yield or protein (in cereals) accordingly. It is also used as a risk management form in many areas across the prairies, as it allows a farmer to first see what crop and moisture conditions are like later in the season to determine if more N is going to pay or not.
Type of N: The sources of N used are usually a dry urea (46-0-0) or a Urea Ammonium Nitrate (UAN 28-0-0). The UAN is less prone to losses through volatilization due to its make up of being only partly urea and the rest in ammonium nitrate form, which is more stable. There are also products out there such as Agrotain and Arborite which are urease inhibitors (NBPT) and can decrease your losses by keeping the N in a more stable form for a longer period of time. Another way to decrease volatilization losses is to apply it just before a rain so that you can get the N brought down into the soil where it can be broken down into a stable form (ammonium). Some of the conditions that cause higher losses are fields with a lot of stubble or trash, higher pH soils, warm soil temperatures and moist conditions.
Application tips: Many farmers apply UAN by dribble banding with streaming nozzles or dribble banding tool bars.. Flat fan nozzles can cause excessive leaf burn, and aren’t recommended. With the other options you may see some leaf burn as well, but plants will grow through it. Try and avoid heat of the day as you may see more leaf burn in hotter conditions.
Crop staging: The stage in which these applications are made can vary depending by what you are trying to achieve with the application. When applying to cereals, applications made prior to or around the 5th leaf stage (GS 30) you can get the N contributing to yield more, where as if applied later on, you may see a bigger bump in protein. In canola, generally speaking, if you can apply closer to bolting you can maximize efficiency and achieve a bigger yield bump vs. applying at the 3-leaf stage, as this is when the canola really begins to use N. Finally, many will apply N with some sulfur (S) to maintain a N:S ratio of 5:1 in canola (5 lb N for every 1 lb S) and roughly a 7:1 ratio in wheat.
Top dressing Nitrogen can be an effective way to get the most out of your crop. A wheat crop needs 2 lb of N per bushel produced, while a canola crop used over 3 lb of N per bushel produced! Keep those numbers in mind when trying to calculate out what kind of a yield bump you would like to accomplish with your application!