Kinetics of Non-exchangeable Potassium Release in Rice-groundnut Cropping System under Alluvial Soils of Odisha, India

Non exchangeable K release can very much influence soil K fertility. The experiment was carried out to investigate the amount of non-exchangeable potassium released from Inceptisols with rice-groundnut cropping system and to use various kinetic equations to describe the release. Release rates of non-exchangeable potassium were determined for five different soils collected from rice-groundnut cropping system fertilized @ 0 and 40 kg K ha-1 over three years. The non-exch K release rate was studied by successive extraction with 0.01M CaCl2 methods. The results show that the proportion of exch.K and non-exch.K to total K varied between 2.76 to 4.95% and 8.39 to 9.95%, respectively. Per cent of clay or silt+clay correlated significantly with water soluble, exch. and non-exch. K. Five mathematical models (elovich equation, power function, parabolic diffusion, first and zero order equation) were used to describe cumulative K release pattern. The elovich and parabolic equation described the K release kinetics satisfactory as evidenced by the highest correlation coefficients and lowest values of standard error of estimates (SEE). The release of Step-K and CR-K was higher in state recommend dose (SRD) than K control which concluded that the SRD of K (40 kgha-1) is adequate to sustain the productivity of intensive rice-ground nut cropping system in alluvial soils of Odisha.