Dhillon, S.K.Dhillon, K.S.2014-09-042014-09-041990Geoderma, 47(1990) 283-300http://hdl.handle.net/123456789/5318Release of K from seven benchmark soils of' India representing Red (Allisols), Black (Vertisols) and Alluvial (Ineeplisols) soil groups was investigated using cation exchange resins saturated with H + .Ca2, Na' and NH4 . Over cumulative reaction periods ranging from 0.25 to 2467 h, efficiency of different cation-saturated resins to replace non-exchangeable K from soils was in the order: H+>C'a2'>Na ' >NH4.,' . Alluvial and Red soils released, respectively, the highest and the lowest amounts of K to H -resin. All other resins were more effective in desorbing K from smeclitic Black soils than from Alluvial soils, having restrictive interlayer space, or Ked soils, containing most of K in the feldspars, From the plots of cumulative K release versus square root of lime, values of surface K and internal K were calculated. Proton- and Ca2' -saturated resins desorbed more internal K from Black soils, whereas Na ' and NH4/ -resins were more efficient in desorbing internal K from illitic Alluvial soils. Potassium release data could be described by first-order and parabolic rate equations. Correlation coefficient and standard error of estimates obtained from least square regression analysis showed that the parabolic diffusion equation could explain belter the kinetics of K release, indicating that exchange of K was diffusion-controlled. Potassium release data also conformed to the radial diffusion equation. Diffusion coefficients were calculated lor three parts of the reaction, corresponding to (I ) 0.25-37, (2) 37-331 and (.1) 3.11-2467 h, representing K release at a fast, intermediate and slow rate, respectively. Diffusion coefficients with different resins were in the same sequence as observed lot cumulative amounts of K released.enArticle