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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.

: An empirical method to estimate rapidly both mean total layer charge and location of charge in smectites and vermiculites is presented, involving exchange with a longchain alkylammonium ion before and after the Greene-Kelly test. The method utilizes an empirically determined relationship between XRD basal spacings and the mean layer charges calculated from the conventional n-alkylammonium ion-exchange technique using simple linear regression models to describe the relationships for both monolayer-bilayer and bilayerpseudotrimolecular layer transitions. The method provides a rapid estimation of these charge parameters and facilitates the proper identification of both smectites and vermiculites consistent with the AIPEA criteria for classification based on total layer charge. It is considered superior to conventional methods of differentiation based mainly on expansion and collapse behaviour.

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