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Fluid Journal : Fluid Journal 2005-2007
ESN, a polymer coated urea, has been quite effective compared to uncoated urea and other N sources. This technology slows the dissolution and hydrolysis of the urea granule by encapsulating urea in a polymer shell, quite different from Agrotain. This slowed solubility makes possible the placement of ESN in direct seed contact without seedling damage as would occur with uncoated urea. Slowed solubilizing of urea also allows a gradual supply of N to reach the plants, limiting the speed of nitrification and, subsequently, nitrate leaching and denitrification. Broad application of this technology to small grains, forages, row crops, and specialty crops has been documented (Figure 2). Old standbys Ammonium sulfate, acidic by nature, is subject to very few problems in terms of NUE. Volatilization of ammonia is less likely and the material is both a good source of ammonium N and sulfate sulfur. Disadvantages include a more serious effect on soil acidity and a relatively low N content. Anhydrous ammonia does not really fit in the same class of the other N materials discussed. Subsurface placement means that volatilization losses are low when Figure 2. Volatilization reduction using ESN in no-till corn, Gordon, KSU, 2003-05. 155 183 177 172 202 199 194 214 215 0 50 100 150 200 250 Corn Yield (bu/A) 80 160 240 N Rate (lbs/A) Urea Ammonium nitrate ESN Table 3. N-GUARD effects in UAN on no-till corn yields, Maryland, 2005. N rate Method of application Grain yield lbs/A bu/A 0 71 90 Band 104 90 Band + 1% N-GUARD 131 130 Band 130 130 Band + 1% N-GUARD 158 Mattapeake loam soil Ron Mulford, Univ. of Maryland applied at proper depth and in soil conditions that ensure a good soil seal around the ammonia knife and over the retention zone. High concentrations of ammonia act as its own nitrification inhibitor and have positive effects on P that is injected in proximity to the ammonia retention zone. However, anhydrous is difficult to use in high-residue situations unless applied in strip-till systems or with a coulter close to the seeding zone. Ammonia, while a low cost fertilizer and an excellent N fertilizer agronomically, has a high cost of application, cannot be blended with other fertilizers, and is also under scrutiny because of safety and handling concerns. Managing volatilization The goal in managing volatilization should be to minimize time of exposure of urea and/or ammonium N forms. Obviously, incorporation is the best protection but may be impossible in many situations. If incorporation is not possible, consider some of these options: • Band UAN instead of broadcast • Watch the weather and apply before rain • Use less volatile sources • Monitor crop and add additional N if necessary. Conclusion In the final analysis, there are a variety of options available for N management where ammonium nitrate has been a preferred N source. Careful management of conventional fertilizers, such as appropriate placement and timing, can enhance their effectiveness. New products on the market, such as coated fertilizers and additives, provide opportunities for high efficiency of urea-containing products, efficiencies that rival that of ammonium nitrate. Some of these practices and products are inexpensive, some are more costly, but all have the ability to be a good investment for crop production through improved NUE. Dr. Blaylock is senior agronomist, Agrium, and Dr. Murphy is president of the FFF. 22 Fluid Journal FALL 2006
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