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Extraction and Colorimetric Determination of Urea in Soils¹

ABSTRACT

A simple colorimetric method of determining urea in soils is described. The soil sample is extracted with 2M KCl containing a urease inhibitor (phenylmercuric acetate), and the extract is analyzed for urea by measurement of the red color formed when an aliquot is heated with diacetyl monoxime and thiosemicarbazide under acidic couditions (phosphoric acid-sulfuric acid medium). The method is sensitive and precise, and it gives quantitative recovery of urea added to soils. The extraction performed is satisfactory for determination of exchangeable ammonium, nitrite, and nitrate by steam distillation methods.

¹ Journal Paper no. J-6484 of the Iowa Agr. & Home Econ. Exp. Sta., Ames. Project no. 1070. This work was supported in part by the Tennessee Valley Authority.

² Research Associate and Professor, respectively, Department of Agronomy, Iowa State University, Ames.

Received for publication February 24, 1970. Accepted for publication September 1, 1970.

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