ISSUE 7 June 16, 2005
TOP-DRESSING N FOR SMALL GRAINS
For yield, top-dressing should be conducted using streamer bars or nozzles before jointing. Not only should the application be made prior to jointing, however, rainfall must move the N into the soil so that the roots can take it up prior to that growth stage. Use of extra N past that growth stage will often result in increased protein, but not yield increases.
For protein enhancement, extra N applied before heading using stream technology not incorporated into increased yield will be used for protein. However, a better approach would be to wait until just after heading and apply a foliar application of 10 gal/a (30 lb N) as 28%, mixed ˝ and ˝ with water at the watery-ripe stage of kernel development (right after pollination, but before starches have formed). This would be applied as a foliar application during the cool of the day. Sometimes despite best efforts there is some leaf burning, although if the precautions previously mentioned were taken, the effects will not normally be severe.
It is highly recommended that no fertilizer N be applied during small grain heading. Often, scab fungicides are applied at this time for maximum effect. Fertilizer should not be applied during a heading application.
There have been questions regarding use of other liquid N products besides 28%. 28% has been know to result in foliar burn sometimes, so alternatives have been suggested. One alternative is 25-0-0, a manufactured urea solution. Some studies have shown this material to be less likely to burn foliage than 28%. However, it is often more expensive to use, so the pros and cons of using this product should be weighed.
Is it possible to make a homemade 25-0-0? On paper, yes. However, when urea dissolves in water it absorbs heat. The sides of the container turn frosty, and unless the solution is heated the full amount of urea doesn’t dissolve. Manufacturers sometimes add sulfuric acid or anhydrous ammonia to the solution to generate enough heat for the urea to fully dissolve. In my own experience, a 14-16% solution is possible on a home-made basis, but the results will probably not be consistent unless a heavy duty liquid fertilizer blender is available. Considering all the trouble and extra expense of alternatives, 28% is a good choice.
Extension Soils Specialist