Release Pattern of Non-labile Potassium in Some Entisols, Inceptisol, Mollisol and Alfisols of West Bengal

A study was conducted to assess the reserve of nonexchangeable potassium in three Entisols, three Alfisols, an Inceptisol, and a Mollisol of West Bengal. The reserves of step K and constant rate K were evaluated in these soils by repeated extraction with boiling nitric acid. The threshold level of K in soil solution below which the release from initially nonexchangeable K reserve starts was also measured for the given soils. The trend of the thres hold K values follow the same sequence as the amounts of specifically held K and total nonexchangeable K reserves in the soils, which in turn, was found to be related to the illitic mineral content of the clay fraction of the given soils. The step K and constant rate K were further correlated with the reserve of the ‘intermediate K’ as well as the amount of exchageable K which was specifically held in wedge zones. The importance of the study in terms of the possible contribution to plant available pool of soil K from initially nonexchangeable K (i.e., “intermediate K”) reserves in the given soils has been pointed out.