The purpose of this study was to assess the trioctahedral mica –K of clay of three genetically different soil groups viz., alluvial (Entisols), ferruginous (Alfisols) and black (Vertisols) soils and its release behaviour towards sodium tetra phenyl boron extraction. Total trioctahedral component (TTC) obtained from the area of the 020 peak in between 19.2 and 19.5°2θ showed significant regression with Mg content of clay. The Vertisols were having maximum amount of TTC in the coarse clay fraction with an average of 12.5 per cent whereas the Entisols were having least amount of TTC in the coarse clay fraction (4 per cent). Amount of K released in the first extract and that in total six extracts by sodium tetraphenyl boron from coarse and fine clay fraction yielded poor regressions with TTC, mica content and ratios of two X ray reflections, i.e., I (001)/I (002) of mica But this regression improved significantly when the total trioctahedral components were multiplied with mica content, showing that trioctahedral component coming from mica determines K release
