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Title: A MICROSCALE METHOD FOR COLORIMETRIC DETERMINATION OF UREA IN SOIL EXTRACTS

Author
item GREENAN, NANCY - UNIV OF ILLINOIS
item MULVANEY, RICHARD - UNIV OF ILLINOIS
item SIMS, GERALD

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: A new method was developed for analyzing soil and water for urea, a common nitrogen fertilizer component. The present methods for analysis of urea have problems with reliability, because the samples tend to change over time, resulting in the first samples giving different results than the last samples analyzed in a particular set. Also, the present methods generate significant quantities of chemical wastes. The method developed in this study solves the problem of sample to sample variability by measuring as many as 96 (including 8 reference samples) at the same time. The chemical waste problem is overcome by the use of a microscale technology requiring less than one one hundredth as much chemical reagent. The approach used in this study could be applied to other common soil analysis methods, many of which presently produce substantial amounts of toxic waste products. The inherent accuracy, reliability, and speed of the microplate technology, could also help reduce costs for many kinds of soil analyses. Better, faster, cleaner, cheaper soil analysis procedures, such as this one, may thus encourage the use of soil testing to better fit fertilizer application rates to crop needs, a necessary step in enhancing both profitability and water quality associated with production agriculture.

Technical Abstract: The diacetyl monoxime colorimetric method of determining urea in soil extracts was modified for microplate format. A 100 microliter aliquot of extract was treated with color reagent in a disposable plastic microtiter plate (96 wells per plate), and color was developed by heating the plate in a low-temperature oven at 87 C for 55 min. After cooling for 20 min at ambient temperature, absorbance measurements were simultaneously performed on all 96 wells using a microplate reader. Analyses by the microscale method were much more rapid and convenient than by the conventional method; moreover, the volume of waste was markedly reduced. Studies to compare the two methods showed very little difference in accuracy, precision, or sensitivity.