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Potassium Adsorption and Release Characteristics on Vertisols of North Western Ethiopian Highlands

ABSTRACT The availability of plant nutrients in soils is governed by adsorption, desorption, and other chemical and physical processes. The adsorption characteristics of applied potassium (K) and the release kinetics of nonexchangeable fraction of soil K for plant nutrition on Vertisols of East Gojjam, North West Ethiopian highlands, were evaluated using the batch equilibrium technique and calcium chloride (CaCl2) solution, respectively. The mineralogy was assessed by X-ray diffraction (XRD). The result indicated that the adsorption data well fitted with the Freundlich and Langmuir models. The adsorption of K was controlled by cooperative adsorption ( > 1) and a partition factor ( < 1). Adsorption parameters were significantly (P< .05) correlated with the cation exchange capacity (CEC) of soils. The highest and lowest external requirement of K optimized from Freundlich isotherm were 1798.15 kg ha−1 and 73.18 kg ha−1 K, respectively, in which the requirement of K was a function of the adsorption capacity and adsorption maxima of soils. Based on the coefficient of determination (R2), the parabolic diffusion and the power function equations displayed the best fit of the kinetic data. The kinetic model confirmed that the release of K is diffusion controlled and indicated that the release of K was from interlayer positions. The rate constants of the parabolic diffusion and the power function models were related (r = 0.62* and 0.66*, respectively) to the uptake of K, suggesting the contribution of nonexchangeable K to plant nutrition. Considerable differences in the release rates were due to the supplying power of K by soils associated with the random ordered illite-smectite minerals and CEC of soils.