Study on the kinetics and rate of soil nonexchangeable K release by three various extraction

The better extracting method and kinetic model for describing the release and rate of soil non exchangeable K were discussed with Elovich, Second order kinetic models by 0.50 mol L-1 HNO3, 0.01 molL-1 oxalic acid and H resin successive extraction under constant temperature and pot exhaustion of ryegrass. The results showed that Elovich equation fitted by the data of H resin extraction perfectly described the release and rate of non exchangeable K. The correlation coefficients of the equations came up to the most significant standard (r=0.982～0.996), and standard errors between the calculations of non exchangeable K releasing capacities by the equations and the estimates by H resin extraction were only 1.35～2.48. The releasing rates of non exchangeable K at various time calculated by Elovich rate equation of H resin extraction were most significantly correlated with the amounts of non exchangeable K absorbed by ryegrass (r=0.944～0.963). It was suggested that Elovich model and H resin extraction could be used as perfect model and method to describe the release and rate of soil non exchangeable K. The results also showed that the release rates of non exchangeable K in illitic soils, including soil 2, 3 and 8, were much higher than those in kaolinitic and montmorillonitic soils.