NUTRIENT ADSORPTION-KINETICS OF ION-EXCHANGE RESIN CAPSULES - A STUDY WITH 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 representing many soil orders were measured in saturated soil paste during 14 d incubation periods. Suppressed ion chromatography was suitable for simultaneous determination of five cations in extracts from the resin capsules. The fractional power equation described well the cumulative nutrient adsorption by the resin as a function of time for all nutrients. The constants a and b in this equation combine quantitative levels of nutrient availability as well as transport and release mechanisms in the soil. Ranges of a and b in soil are presented and their relationships to other soil properties are discussed. A simple method for calculating kinetic constants in the power function based on only two incubation times is proposed. The Phytoavailability Soil Test method offers great potential for standardized, multi-element soil testing in many environments. Some aspects of its suitability for use in standard soil testing for rice are discussed.