Published online by Cambridge University Press: 27 March 2009
Six soil series differed in water-soluble, exchangeable and nonexchangeable K. Significant positive relationships were observed between exchangeable K and water-soluble K. A highly significant positive relationship was found between the K saturation of the cation exchange complex and water-soluble K in the individual soil series, and when the six series were pooled; K saturation, therefore, may predict water-soluble K in a range of tropical soils. Potassium desorbed in 35 min by electroultrafiltration (EUF) may serve as a measure of exchangeable K in predominantly kaolinitic tropical soils. In soils with appreciable amounts of mica, longer K extraction by EUF (up to 70 min) may indicate the reserves of nonexchangeable K.