ISSUE 4 May 25, 2006
DELAYED N APPLICATIONS
Due to high N prices and the rush to seed, some fields are still in need of supplemental N. Top-dress applications are made to solid-seeded crops, while the term side-dress applies to row-crops of all types.
In small grains and other solid-seeded crops, the best method of top-dressing is with streamer-bars. These gadgets fit onto the nozzle outlets of a spray boom and branch out into tees, ending in an orifice that allows a straight-stream of liquid to be projected out the end. The straight-stream is preferable to a broadcast liquid because it has much less leaf burn potential and because urea volatilization is minimized due to the concentrated band. The down side to this type of application, and the reason that NDSU does not recommend it as a primary source of N, is that it should be considered a soil and not a foliar application. Because it is a soil application it must have rainfall of some substantial amount in order for roots to pick it up and become useful for the crop. In the case of delayed application, or a need for supplemental application in-season, there is no better choice but to use the top-dress streamer-bar method. Another option would be to broadcast dry urea, however, if substantial rainfall does not fall for a week or more, more of the urea application is subject to loss than the liquid N (28%, UAN) streamer-bar option.
Most side-dressing is made using anhydrous ammonia. It appears from recent industry reports that the cost of anhydrous has dropped substantially from the high of mid-winter pricing. That may result in lower costs to growers, depending on what buying position was taken by the local retail outlet during the turbulent winter/spring period. Regardless, anhydrous is usually the preferred material for side-dressing due to its cost relative to other products and the availability of tools that are easily adapted to between row application. As in preplant applications, the ammonia should be placed at least 4 inches into the soil to prevent leakage to the air. Rates are safe to the crop at least to the maximum recommended, as long as the application knife is located between the rows.
Other side-dressing options include liquid N (28%) between the rows and cultivation of urea. Liquid materials do not need to be placed as deeply as anhydrous. Placing them a couple inches deep using an application knife and some type of slot closure, such as an offset disc or disc pairs will do an adequate job of coverage. Urea can be applied to some row crops broadcast and cultivated in, but not to corn. Some urea will be trapped in the whorl and will burn the corn leaves badly. If cultivating urea for corn, some method of delivery between the rows should be used.
There is no N source available today that has been shown to be more efficient in nutrient delivery than our standard commercially available products. New products are being tested and some have been tested in the past, but for now, I know of no products where a grower can reduce rates and achieve the same results as the products used in the past. Curiosity regarding these products is understandable, but growers should confine their use to small check areas.
Dr. Dave Franzen
NDSU Extension Soil Specialist