Note: While we do mention the “1.2 rule” in this article, we here note that the nitrogen rate guidelines are changing for Illinois. Reference Dr. Emerson Nafziger’s recent article in the U of I PMCDB

Producers determined to apply anhydrous this fall need to keep a few things in mind, especially in the light of currently stressed budgets. As usual, anhydrous should not have been applied until after soil temperatures settled around 60 degrees and should not have been applied until after the third week in October. Strict adherence to an application rate of 1.2 pounds of nitrogen per each proven bushel of corn is a worthwhile goal as well. Finally, if anhydrous is to be applied this fall it should not be applied minus a nitrification inhibitor in central and northern Illinois.

Nitrogen in anhydrous eventually can be lost to the air or lost to ground water. This gaseous product has a well known affinity for moisture that results in it “morphing” from ammonia (NH3) into ammonium (NH4). Ammonium is positively charged and easily held by soil particles thus reducing nitrogen loss. However, bacteria in the soil eventually convert ammonium from this stable state into a less persistent state termed nitrate. Nitrogen can therefore be lost via conversion to a gas (termed denitrification) or via leaching. Nitrosomonas bacteria first convert ammonium into nitrite (NO2). These bacteria are then followed by other bacteria (Nitrobacter spp.), which convert that nitrite into nitrate (NO3). The process of converting ammonium into nitrate is termed “nitrification.”

Why do these bacteria “bother” ammonium? Like other organisms, they “do what they do” to stay alive. Nitrosomonas bacteria oxidize (add oxygen to) ammonium eventually forming nitrite (NO2), a toxic/poisonous compound, which is quickly oxidized to form nitrate (NO3), a non-toxic compound. Both nitrosomonas and nitrobacter species are termed lithotrophic bacteria. In other words, they procure the energy needed to stay alive from inorganic compounds rather than from sugars. As nitrosomonas and nitrobacter oxidize their respective nitrogren materials (via a complex of various enzymes), an electron is removed and passed along what is termed an “electron chain.” Such electron chains eventually move an electron to one side of membranes found in the mitochondria of the bacteria. Pulled with those electrons are positively charged protons which “build up” on the “far side” of these mitochondrial membranes. As the protons drift back through, in an effort to reestablish equilibrium, they interact with molecules embedded in that membrane. The resulting interaction, as protons pass by these molecules, “harvests” energy needed to keep the bacteria alive.

So how do nitrification inhibitors work? Nitrification inhibitors apparently tie up certain materials needed to form enzymes in nitrosomonas bacteria. The specific enzymes disrupted are those needed to oxidize ammonium. When this “ammonium oxidase” complex is disrupted, electrons are no longer captured. No captured electrons means no movement of electrons along the electron transport chain. A seized electron transport chain equals no dragging of protons across mitochondrial membranes. Simply put, bacteria cannot procure energy they need which results in death. In other words, nitrification inhibitors are bacteriacides. Nitrosomonas bacteria are reduced in number, for a time, which results in nitrogen retention in the stable/easily reatained ammonium form for a more extended period of time than normal.

Nitrification inhibitors will perform best when the activity of nitrosomonas bacteria has already slowed down. In other words, the environment must be cold and it must stay cold. Otherwise surviving bacteria would recover, the population would bounce back, and significant nitrification would resume (thus the explanation why anhydrous applications with an inhibitor should not occur before sixty degree soil temperatures and not before the third week in October). Nitrification inhibitors also benefit the producer most when nitrogen rates hit or fall just beneath 1.2 pounds of nitrogen per each proven bushel of corn. The benefits of such inhibitors will also be on display when saturated, denitrifying, conditions persist.

OTHER REMINDERS CONCERNING NITROGEN

• ANHYDROUS – Remember, the closer this product is applied to use by the crop the better the return on investment. Nitrification inhibitors, while beneficial in much of central and northern Illinois, will not benefit the producer on sandy soils.

• AMMONIUM SULFATE – U of I Extension recommends that ammonium sulfate not be applied until after soil temperatures settle below 50 degrees for several days. In addition, losses will be reduced (i.e. return on investment will be greater) if AMS applications are held off until the second week of November in central Illinois. Slopes in excess of five percent should not be candidates for ammonium sulfate in the fall or winter.

• UREA – Urea-containing fertilizers should not be applied to “designated corn” ground in the fall or winter.

U of I Extension Sangamon-Menard Unit Crops 11/04/05
Matt Montgomery, Crop Systems
P.O. Box 8467
Springfield IL 62791
(217) 782-4617