University of Illinois assistant professor of crop sciences Fabián Fernández offers some guidelines for fall nitrogen application.
"Anhydrous ammonia (NH3) and ammonium sulfate ([NH4]2SO4) are the only nitrogen sources recommended for fall application. Ammonia transforms quickly to ammonium (NH4+), and nitrogen in ammonium sulfate is already in the ammonium form. Ammonium is absorbed into the exchange sites in soil particles and organic matter, protecting it from leaching.
Nitrogen sources containing nitrate (NO3-) should not be used in the fall. Nitrate does not become absorbed into exchange sites in the soil and can be easily leached or denitrified long before the plants are ready to use it. Common fertilizers that contain nitrate include ammonium nitrate (NH4NO3) and urea ammonium nitrate (UAN).
Ammonium sulfate is an excellent source for no-till fields where broadcast applications are preferred. It is always best to apply it before soils freeze so the fertilizer can dissolve and rain can incorporate it into the soil.
Organic fertilizers derived from animals (manure, poultry litter) are good fertilizer sources that can be used in the fall. These products supply nitrogen as well as phosphorus, potassium, and other crop nutrients, and are often less expensive than inorganic fertilizers."
"Although recommended management practice may not work very well every year because of environmental conditions beyond our control, I emphasize that these guidelines, if followed, will ensure the greatest chance to protect your nitrogen investment and at the same time enhance environmental protection," said Fernandez.
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