Top-dressing nitrogen (N) is becoming a more common practice across western Canada; and for good reason. Achieving superior yields, better quality, risk management and higher nitrogen use efficiency are few benefits that are drawing more attention to this practice. To really power up your top dressing application the consider a variable rate application to put the N were you will be able to increase your return on investment. Varying your rate of N will also promote overall standability and can often be the difference between seeing a yield bump and having a flat crop at harvest. But what else do you need to take into account when getting into the business of top dressing?
1. Nitrogen Source
The sources of N used are usually a dry urea (46-0-0) or a Urea Ammonium Nitrate (UAN 28-0-0). There also has been an increase in the interest of melted urea (liquefied or dissolved urea). UAN is a stronger candidate due to the forms of N available in the product and the speed at which half of it is available to the crop. The option to use nitrogen stabilizer products such as Agrotain can help maximize the N use efficiency and minimize losses. Applying the N just before a rain so that you can get it moved down into the soil where it can be taken up by the plant and isn’t as susceptible to fosses. Be weary of high trash levels on the soil surface as the old plant material can tie up nitrogen.
2. Targeted Yield Bump
Be sure you know how big of a yield bump you are targeting in certain areas or across the whole field (or by yield zone) as this will give you the opportunity to accurately determine how many pounds of N you need to apply to see that yield increase. For example canola will take up 3.3lbs/bu of N, so if you see potential for 10 more bushels of canola with the current conditions you would need over 30lbs of actual N applied.
3. Crop staging
The stage in which these applications are made can vary depending by what you are trying to achieve with the application. Knowing your desired outcome, being conscious of field conditions and crop stages is going to help you get the return you are aiming for. There is essentially a teeter-totter situation in cereals with protein and yield; after the 4-5 leaf stage the N will shift from primarily increasing yield to impacting protein content more so than yield. If you are aware of the potential quality spreads then top dressing can also make the return of this practice much more lucrative over and above just a yield increase. In canola you are trying to apply based on when the crop will increase N uptake which begins to really occur just prior to the green bud-bolting stages.
Shifting nitrogen application practices to an in season top dress can benefit many different operations. Managing the big things like the source of N as well as the smaller things like application timing and conditions makes for a strategy that will yield higher profits.