Nitrification Inhibitors For Corn Production.pdf

Ammonium (NH4+) added to soils or formed by decomposition of organic N compounds is oxidized to nitrite (NO2) by Nitrosomonas bacteria, and nitrite is further oxidized to nitrate (NO3) by Nitrobacter bacteria in a process termed nitrification. Nitrate is normally the form of N taken up by plants; however, most plants can also assimilate ammonium. In most soils, nitrification of applied ammonium is rapid (2-3 weeks), but nitrification rates are greatly reduced by cool soil temperature (50°F), low pH (5.5), and waterlogged conditions.

Only about 50% of the applied N is taken up by corn during the year following fertilizer addition. About 25% is immobilized during residue decomposition or remains in the soil as nitrate. The remaining 25% is lost from the plant rooting zone by leaching and/or denitrification. Leaching is important in coarse-textured soils, where nitrate may be leached from naturally well-drained or tile-drained soils by percolating water. Denitrification is the major pathway of N loss from most fine-textured soils, occurring in soils that become waterlogged by excessive rainfall or irrigation.

Nitrification inhibitors (NI) are chemicals that reduce the rate at which ammonium is converted to nitrate by killing or interfering with the metabolism of Nitrosomonas bacteria. The loss of N from the rooting zone can be minimized by maintaining applied N in the ammonium form during periods of excess rainfall prior to rapid N uptake by crops. N-Serve and Dwell are currently the only U.S. Environmental Protection Agency-approved nitrification inhibitors for use on cropland in the United States.

N-Serve and Dwell may be applied as a band application with anhydrous ammonia or N solution fertilizers, or impregnated on solid fertilizers or mixed with N solution fertilizers prior to broadcast applications. Higher rates of N-Serve and Dwell are often required to control nitrification of broadcast ammoniacal fertilizers. Recent studies have shown that NI can also be effectively used with liquid animal manures and sewage sludges that are injected into the soil.

A number of studies throughout the United States have demonstrated that NI effectively retards the conversion of ammonium to nitrate in a variety of soils. Results indicate that application of NI delays the conversion of ammonium to nitrate for 4 to 10 weeks, depending upon soil pH and temperature. With fall applications of N fertilizers, NI minimize nitrification until low soil temperatures (40°F) stop the process. With spring applications, NI prevent the formation of nitrate during the late spring when rainfall is high and uptake of N by crops is low.

Corn yields are often increased as N losses from soils are reduced by the application of NI with both conventional tillage and reduced tillage systems. The potential benefit from NI application depends on a number of site-specific factors, such as soil type, climate, cultural practices, and N management program. Highest probability of yield response from NI occurs with excessively drained or poorly drained soils because of N losses from leaching and denitrification, respectively.