NUTRIENT ADSORPTION-KINETICS OF ION-EXCHANGE RESIN CAPSULES - A STUDYWITH SOILS OF INTERNATIONAL ORIGIN

A method based on use of ion exchange resin capsules was evaluated for simultaneous extraction of plant available nutrients (N, P, K, Ca, Mg , and Na) to determine its utility as a general soil testing procedure for soils of world-wide origin. Nutrient release kinetics of soils re presenting many soil orders were measured in saturated soil paste duri ng 14 d incubation periods. Suppressed ion chromatography was suitable for simultaneous determination of five cations in extracts from the r esin capsules. The fractional power equation described well the cumula tive nutrient adsorption by the resin as a function of time for all nu trients. The constants a and b in this equation combine quantitative l evels of nutrient availability as well as transport and release mechan isms in the soil. Ranges of a and b in soil are presented and their re lationships to other soil properties are discussed. A simple method fo r calculating kinetic constants in the power function based on only tw o incubation times is proposed. The Phytoavailability Soil Test method offers great potential for standardized, multi-element soil testing i n many environments. Some aspects of its suitability for use in standa rd soil testing for rice are discussed.