Questions often arise regarding the use of nitrification inhibitors (N-serve) with nitrogen (N) fertilizer sources. There will be an even greater interest following 1996 when N losses were widespread throughout the area. The following is a summary of how nitrification inhibitors work, the potential benefits they offer, and when they most likely result in an economic return.
Nitrogen is extremely dynamic in soil----always changing or moving. Crop producers are most interested in two major forms of N: ammonium (NH4+) and nitrate (NO3-). Both forms are available for crop growth but each has its own unique properties. Ammonium N is positively charged and held by the negatively charged soil particles. It is not subject to loss when soils are waterlogged and a biological process called denitrification takes place. Nitrate N, on the other hand, is negatively charged and not held by soil particles. It is subject to both leaching (movement down from the crop's rooting zone) and gaseous loss to the atmosphere from denitrification.
When ammonium-N is added to the soil, it is subject to a process called nitrification whereby soil bacteria called nitrosomonas convert the ammonium to nitrate. If ammonium-N is not immediately taken up by plants, it will soon be converted to nitrate and subject to losses from leaching (primarily on sandy soils) and denitrification (medium and fine-textured soils). These losses were very obvious and significant during the past growing season. This conversion is strongly temperature dependent and occurs quickly under warm soil temperature conditions but stops entirely when the soil is frozen. The use of a nitrification inhibitor (NI) will stop or slow down the conversion of ammonium to nitrate and reduce the chances for N losses.
The ultimate goal of any NI is to increase the efficiency of the N fertilizer applied. For an economic benefit to occur, the N saved from denitrification/leaching losses by using the NI would have to result in a yield increase for the corn crop with a value greater than the cost of the NI. The greatest likelihood for N losses are on sandy soils, poorly drained soils, or when nitrogen is applied in the fall. It is in these same situations where the use of a NI would have the most chance for economic return. Conversely, we would not recommend the use of a NI on well-drained medium textured soils or when N is applied as a sidedress application.
Since NI products influence only the reaction of ammonium to nitrate, they can only be used effectively on fertilizer products that contain or convert to the ammonium form. These include anhydrous ammonia, 28% nitrogen solution (urea ammonium nitrate), ammonium sulfate, ammonium nitrate, urea, and liquid manure. The higher percentage of ammonium contained in the fertilizer, the more effective the NI will be. N-serve, itself, is an extremely volatile product and can be easily lost if not incorporated into the soil surface. It will also be more effective when the fertilizer is applied in a band versus broadcasting.
Many research trials have confirmed NI products such as N-Serve are effective in delaying the conversion of ammonium to nitrate. These same trials show a wide range of results from the standpoint of cost-return benefits depending upon soil type, drainage, time of N application, and environmental conditions. The use of NI products should be viewed as a form of risk insurance. In some years there will be no benefit while in others significant yield responses will occur. How much a producer is willing to invest in this type of insurance is a personal decision. In Fond du Lac County, the highest likelihood for response will come on poorly drained soils or when N is applied in the fall for either corn or wheat. There is little merit for using a NI when N is sidedressed for corn or on medium textured, well drained soils where N losses are rare. They should also not be used as a means of reducing N applications below recommended rates.
For more information contact Mike Rankin|
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