Preparation of aqueous soil extract

The An + A12 horizons from a Udorthent soil, representative of the Kokokahi clay series, was used. This was of the mont-morillonitic, isohyperthermic family, located at the island of Oahu, Hawaii (ref. 357). 

Microanalytical Service Ltd., Vancouver. The total Ca, Mg, P, Na, K, and Fe were determined by Dr. Carmen Mazuelos (Centro de Edafologia, CSIC, Sevilla, Spain) with a Perkin-Elmer Model 703 absorption spectrophotometer. The infrared spectrum of the lyophilized material was taken on KBr pellets (1 mg sample in 200 mg KBr) with a Perkin-Elmer Model 337 infrared spectrophotometer. X-ray diffraction analysis was carried out by Dr. Carmen Hermosin, Centro de Edafologia, in a Philips PW 1010 diffractometer using Ni-filtered, CuKoc, radiation operated at 30 kV and 20 mA, scanning speed of l°/min, time constant 2, and range of diffraction angles from 2 to 60°. 

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