Nitrification inhibitors can be used with fertilizers containing ammonium nitrogen. These temporarily suppress populations of Nitrosomonas bacteria in soil, which convert ammonium to nitrate. Nitrification inhibitors are primarily used to reduce the potential for N loss through leaching or denitrification of nitrate. The primary nitrification inhibitor available in Nebraska is N-Serve. Urease inhibitors temporarily block the function of the enzyme urease, found in soil and plant residues, which breaks down urea into ammonium. Urease inhibitors help limit the potential for ammonia volatilization from urea. The primary urease inhibitor available in Nebraska is Agrotain.
The use of inhibitors with N fertilizer is one approach to increasing N use efficiency. Another approach is to use N fertilizers which physically or chemically slow the rate of N release to the soil. These forms of N fertilizer have been available for many years, but their use has been limited to turf and horticultural applications due to their cost. As the cost of N in general has increased, the relative added cost for slow release formulations has declined, and new formulations intended for application to agronomic crops have been developed.
The primary form of N which physically slows the rate of N release is urea coated with a semipermeable plastic shell. This coating allows water to diffuse through the shell, dissolving urea, which then diffuses back through the shell at a controlled rate. The rate of diffusion can be regulated with the chemical makeup of the coating and its thickness. Fertilizer using this type of polymer coating for urea is available in Nebraska as ESN, manufactured by Agrium or Polyon, and sold by Simplot.
The second type of slow release N fertilizer is the general category of urea formaldehyde or methylated urea. This form of fertilizer has carbon-based chains of various lengths containing urea. The release rate of N is controlled by the lengths of the carbon chains, and the composition of compounds of different chain lengths along with urea in the fertilizer formulation. I am not aware of fertilizer products based on this technology currently being sold in Nebraska for agronomic crops.
The use of inhibitors for improved N availability has been researched in Nebraska and other Midwestern states for many years, and there are good guidelines for when and how these products should be used. They are not a guarantee of increased yield, but rather a form of insurance that N availability may be increased if environmental conditions are conducive to N loss.
The use of N fertilizers which have physical or chemical slow release characteristics has not been studied very much in Nebraska for agronomic crops. Preliminary research in Nebraska and other states suggests these fertilizers have good potential for increasing N use efficiency. They may allow efficient N use with single rather than split applications, thus eliminating the cost of multiple trips across the field. The University of Nebraska does not currently have any guidelines on how to best use these fertilizers cost effectively. There are research and demonstration efforts underway evaluating slow release N fertilizers, comparing them to current management practices. We encourage producers to become familiar with slow release N sources which may be available in their area of the state and to watch for results from these projects. If producers are interested in using slow release formulations, we suggest using them initially on a limited basis and carefully following the companies’ guidelines for their use.
Richard Ferguson
Extension Soils Specialist
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