Kinetics of Nonexchangeable Potassium Release by Organic Acids from Mineralogically Different Soils

A considerable fraction of soil K, occurring as nonexchangeable form, is released by organic acids. The kinetics of nonexchangeable K release by organic acids in illite (Inceptisols), kaolinite (Alfisols) and smectite (Vertisols) dominated soils were investigated. Malic acid extracted larger amounts of K compared to acetic acid and citric acid. Cumulative K released by each of these acids was positively correlated with nonexchangeable K. The Vertisols showed highest cumulative K release followed by Inceptisols and Alfisols. However, in the first hour, Alfisols showed higher per cent of K release than that of Inceptisols and Vertisols. The parabolic diffusion equation describes tl;1e rate of K release explicitly, followed by first order reaction. Release rate constants also confirmed that smectitic-Vertisols maintained higher release rate as compared with kaolinitic-Alfisols and illitic-Inceptisols.