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Fluid Journal : Early Spring 2011
5 The Fluid Journal Early Spring 2011 dependent on soil pH, soil moisture, and on soil temperature. There is no standard method yet to determine the SRN in solid slow-release fertilizers. The slow-release committee of the American Association of Plant Food Control Officials (AAPFCO) has been working on a method that could be used universally for this purpose. Controlled release nitrogen fertilizers were formed by incorporating urea in chemical reactions forming bonded urea products that slowly break down in the soil, releasing its N content. Typically, these fertilizers are either solid or liquid products. Triazone-CRN fertilizers are an Summary: A liquid chromatographic method (using a different column, eluent, and operational parameters from AOAC Method 983.01) was developed and has been used for over a decade for the determination of urea in a class of liquid fertilizers noted as not being suitable for urea analyses by present official methods. It was judged a suitable candidate for a collaborative study to provide a methodology for use in cases where present methods are unsuitable. Tessenderlo Kerley, Inc. of Phoenix, Arizona, in collaboration with ten other laboratories (five commercial and five state labs), developed a method based on liquid chromatography. It separates efficiently, clearly, and calculates the amount of unreacted urea from other N-containing compounds present in solution that could be used to determine the amount of control release nitrogen (CRN)/slow release nitrogen (SRN) in solution. A liquid chromatographic method has proved successful for over a decade in determining amount of urea in a class of ﬂuid fertilizers. Urea is one of the most widely used nitrogen-release fertilizers. More than 90 percent of the world's urea production is used as fertilizer. Soil bacteria containing urease enzyme catalyzes the conversion of urea to ammonia and carbon dioxide via ammonium carbonate formation and decomposition. Nitrogen (N) from urea can be lost to the atmosphere if fertilizer urea remains on the soil surface for extended periods of time during warm weather. Urea breakdown can begin as soon as it is applied to the soil. In the presence of the enzyme urease and a small amount of soil moisture, urea hydrolyses occurs and N is lost due to ammonia volatilization (Figure 1). Techniques applied Several techniques have been applied in order to prevent loss of N from urea due to ammonia volatilization. Sulfur-(S) coated urea and polymer-coated urea have been used to prevent hydrolyses of urea and to slowly release N from urea to the soil, hence the term slow release fertilizer has been introduced. Slow Release Nitrogen is a measurable quantity and is defined as that portion of N in a fertilizer that slowly releases to the soil. Slow Release Nitrogen is The Fluid Journal • Ofﬁcial Journal of the Fluid Fertilizer Foundation • Early Spring 2011 • Vol. 19, No. 2, Issue #72 Dr. Michael Hojjatie, Dean Abrams example of fluid fertilizers formed by the chemical reaction of urea. The term CRN is a measurable quantity and is defined as that portion of N in the fertilizer that releases in the soil over time. It is also dependent on soil properties. Unlike the solid slow-release fertilizers and solid control-release fertilizers, there is a method to quantitatively measure the amount of controlled release N in the liquid-controlled released N fertilizers. This method has been approved by the AOAC International and AAPFCO. Delayed release N fertilizers are another term for those fertilizers releasing their N content over time. Determination of Urea in Fluid Fertilizers Containing Water-Soluble Urea-Formaldehyde Reaction Products Figure 1. Environmental losses of N from urea.