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29. Select Nitorgen Fertilizers Wisely
fertilizer chart

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.
field being irrigated On sandy soils, the differences between these forms of nitrogen are especially significant because water and nitrate can leach quickly through such coarse-textured soils. On heavy soils, the differences may not be as significant—unless you use a nitrification inhibitor.
spreader Inhibitors delay the transformation from ammonium to nitrate. They are most effective if the soil is moderately or well-drained and is in an area of heavy rainfall or frequent flooding.
fertilizer tank in field Also, they offer the greatest potential benefits when you fall-apply nitrogen after the soil temperature has dropped below 60 degrees Fahrenheit and the soil is likely to be frozen for most of the winter. They work best when nitrogen is applied at or below optimum levels.
Urease inhibitors chart Urease inhibitors slow the conversion of urea to ammonia. This reduces volatilization, the process in which ammonia on the soil surface is lost into the atmosphere as a gas. With a urease inhibitor, producers can broadcast urea and UAN without incorporation—thus preserving more crop residue. They also no longer need to apply excess amounts to compensate for volatilization. University research has shown urease inhibitors to be very effective when they're needed.
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