ISSUE 3 May 28, 2009
CATCHING UP WITH FERTILIZATION
Many growers wisely seeded crops without waiting for the fertilizer truck to arrive. The following are several options that might be considered to apply nutrients.
For all crops, if P or K is needed, these can be applied to the soil surface as soon as possible after planting. Be careful in any field not to turn too suddenly on the ends, because the soil will mound up and the seed will be disturbed. Crops can feed nicely on surface-applied P and K as researchers have learned over the years in no-till studies. Hopefully the grower has applied a "starter" to those crops that needed it, because the surface-applied P and K will not act like one, but will be utilized later in the season.
For solid-seeded crops, N can be applied as urea or UAN (28-0-0). If applying urea and the forecast is not predicting rain for several days, have the supplier treat the urea with Agrotain® to keep it resistant to decomposition and volatility for about 10 days. This is the product that most consistently inhibits urease the longest. UAN can be applied using stream-bars. Because UAN is half ammonium nitrate, which is not at risk from volatilization, and the application is concentrated, use of a urease inhibitor is not generally required. When using stream-bars on emerged crops, application when the wind speed is low and the stream remains intact is important. If the stream begins to break up in the wind, the application acts like a broadcast application and leaf burning will be severe. Use of low-rate (2-3 gal/acre) slow-release N products have not been shown to improve yields compared with standard rates of UAN or urea, except in cases where tillering might need enhancement in already well-fertilized soils.
For row-crops, use of anhydrous ammonia at side-dress time would be appropriate. In 22-30 inch row spacing, set the anhydrous knife in the center between the rows and make sure that the application slit is being covered by soil. A grower can side-dress any required N rate to any crop without risk of seedling injury if the application slit is covered. It is also possible to side-dress urea and cultivate it in, but few growers have the equipment to do this. In corn, do not broadcast urea over the top, because some urea granules will fall into the leaf whorl and burn the crop. Side-dressing can also be conducted using UAN, either applying the UAN similar to anhydrous using a coulter and a shallow application depth or dribbling the UAN between the rows using stream-orifices. Do not stream-bar UAN over the top of the rows or fertilizer burn will result. Use of UAN is particularly effective in soils too wet to apply anhydrous ammonia.
UREA BEFORE FIRE
There are still corn stalks and other residues that might be burned yet this spring. It is important to remember to apply fertilizer AFTER burning and not before. Urea does not burn, but it can easily be lost if applied before burning. Urea pellets will melt at 260 degrees F; then urea will begin to vaporize at about 280 degrees F. At temperatures about 300 degrees F loss of urea from pyrolitic decomposition is rapid and can be completely decomposed in just a couple minutes. Keep in mind that the temperature of a residue fire can be over 400 degrees F for several minutes as the fire passes through an area. The bottom line is that one cannot count on any urea-N being left on the soil once a fire passes through, so fertilize after the burn.
NDSU Extension Soil Specialist