The following information is a Web Extra from the pages of Farm Journal. It corresponds with the "Crop Tech” department page by Pam Smith. You can find it in the November 2008 issue.
Remember the days when you applied additional units of nitrogen to account for leaching or denitrification? No longer—higher natural gas prices mean you need to hang on to every drop of nitrogen and its smart environmental stewardship.
It also means nitrification inhibitors will play an increasing role in nitrogen management, says Robert Hoeft, University of Illinois extension soil fertility specialist. Farmers who fall apply nitrogen have long depended on the use of inhibitors to make nitrogen less susceptible to leaching and denitrification.
Now, a new product called Inhibit is being introduced by Dow AgroSciences for use with spring applications of urea ammonium nitrate (UAN) and manure applications. The encapsulated product uses the same active ingredient as N-Serve to stabilize nitrogen in the soil. Stabilized nitrogen maintains nitrogen in the ammonium form by impacting soil bacteria.
Here's how it works. When you apply anhydrous ammonia, urea or urea ammonium nitrate, the fertilizer rapidly converts to the ammonium form—which carries a positive charge. That positive charge allows ammonium to be held in place by negatively charged soil and organic matter and doesn't move readily with water. However, when temperatures start to heat up, soil bacteria converts ammonium to the nitrite form and ultimately to nitrate. Nitrate-N carries a negative charge and is repelled by negatively charged soil particles and is mobile in the soil. This whole process can take as little as two to four weeks when soil temperatures exceed 50 degrees.
Stabilized N resists loss because it stays in the positively charged ammonium form longer into the growing season and remains available for uptake by the plant for a longer period of time.
Hoeft says the conversion of ammonium to nitrate does not necessarily mean it's been lost from the soil profile, but it is susceptible to loss in fields that have been saturated with water for several days. In Illinois soils, his research shows 4% to 5% of the amount of nitrate-N present will be lost by denitrification for each day that soils are saturated when soil temperatures are above 65 degrees. If temperatures are below 55 degrees, denitrification losses drop to 1% to 2%.
"Nitrogen inhibitors are better at keeping nitrogen in the original form,” says Hoeft. "Whether you realize a yield boost for that depends on the year.”
Hoeft predicts a spring nitrogen inhibitor should be well received. Wet spring conditions in 2008 caused some growers to lose 15% to 20% of their nitrogen.