Kinetics of release of non-exchangeable potassium by cation-saturated resins from Red (Alfisols), Black (Vertisols) and Alluvial (Inceptisols) soils of India

Abstract

Release of K from seven benchmark soils of India representing Red (Alfisols), Black (Vertisols) and Alluvial (Inceptisols) soil groups was investigated using cation exchange resins saturated with H +, Ca 2+, Na + and NH 4 +. 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 + > Ca 2+ > Na +> NH 4 + . 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 smectitic Black soils than from Alluvial soils, having restrictive interlayer space, or Red soils, containing most of K in the feldspars. From the plots of cumulative K release versus square root of time, values of surface K and internal K were calculated. Proton- and Ca 2+-saturated resins desorbed more internal K from Black soils, whereas Na + and NH 4 +-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 better 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 for three parts of the reaction, corresponding to (1) 0.25–37, (2) 37–331 and (3) 331–2467 h, representing K release at a fast, intermediate and slow rate, respectively. Diffusion coefficients with different resins were in the same sequence as observed for cumulative amounts of K released.