Effect of Soil Minerals on Potassium Release from Soil Fractions by Different Extractants

Abstract

Kinetics of potassium (K) release from sand, silt, and clay fractions of 10 calcareous soils of southern Iran were examined to evaluate the ability of different fractions to release K. Samples were successively extracted with 0.01 M CaCl2, HCl, and citric acid for 1496 h. Mineralogical analysis indicated that mica, chlorite, smectite, and palygorskite were the main minerals detected in the clay fraction. The sand and silt fractions were dominated by quartz, feldspars, and micas. Results indicated that the clay fractions released more K than the silt and sand fractions to all extractants (620, 283, and 148 mg kg−1 for clay, silt, and sand fractions, respectively, averaged for 10 samples and three extractants). The ability of acidic extractants to release K from the sand and silt fractions was much higher than that of CaCl2 solution. However, this difference was not significant (p < 0.05) for the clay fraction. For CaCl2, first-order equation, and for acidic solutions, all first-order, Elovich, and parabolic diffusion equations can describe the release rate of K from different soil fractions. Significant relationships (p < 0.05) were obtained between cumulative K released to three extractants and b and a values of Elovich equation with mica content in the clay fractions. Generally, the data presented here demonstrate the importance of clay fractions in K supply to plants in calcareous soils of southern Iran.