Select nitrogen fertilizers wisely 29 Select nitrogen fertilizers wisely Detailed image. . . 29A. Nitrogen doesn't travel much in the ammonium form. Ammonium compounds grab hold of soil particles and generally stay put. But in the nitrate form, nitrogen begins to move and it's usually downward-leaching into the soil, where nitrate can enter groundwater or drain tiles.
Drain tiles can provide a direct route for nitrate to reach lakes and streams.
Eventually, ammonium forms of nitrogen will transform into nitrate through the nitrification process. But nitrogen sources that contain a greater percentage of ammonia will be less likely to leach initially after application. Of all nitrogen fertilizers, anhydrous ammonia is the least likely to leach initially after application, followed by urea. Third are UAN solutions, which are one-fourth nitrate. Half of ammonium nitrate is in the nitrate form, making it the fertilizer in which the greatest amount of nitrogen is ready to leach immediately after application.