Mathematical Models for Potassium Release Kinetics in Calcareous Soils
1985
Havlin, J. L. | Westfall, D. G. | Olsen, S. R.
Potassium release from the coarse (20–50 µm), medium (5–20 µm) and fine silt (2–5 µm), and the coarse (2–0.2 µm) and medium-fine clay (<0.2 µm) fractions of six Great Plain soils was determined by successive extraction with Ca-saturated cation exchange resins. All soils contained primarily montmorillonite-mica minerals. Results indicated that 65 to 80% of the total K released in 7000 h of extraction time occurred in the clay (<2.0 µm) fraction. Four mathematical models (first-order rate, parabolic diffusion, power function, and Elovich) were used to describe cumulative K release. Comparisons of coefficients of determination (r²) and standard errors of the estimate (SE) indicated that the Elovich, power function, and parabolic diffusion equations adequately described cumulative K release, whereas the first-order rate equation did not. Rate constants for the three equations were highly correlated with mica content and relative alfalfa yield and K uptake. In the past, others have used complex equations containing three simultaneous first-order rate terms to describe K release; however, results reported herein show that simple one-term equations can be used.
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