The stable desorption parts of soil Quantity/Intensity isotherms were used to determine the contributions of initially exchangeable and non‐exchangeable potassium to plant uptake from ten soils. The activity ratio, ARK= aK/√aCa, Mg at which K was first taken up from non‐exchangeable sources varied from 3 × 10−3 to 8 × 10−3 M1/2 depending on the soil. Uptake rates of two categories of initially non‐exchangeable K were linearly related to √times;. The first category appeared to be close to equilibrium with the initially exchangeable K, and gave effective diffusion coefficients of 10−7 cm2 s−1 for four soils. The second category gave diffusion coefficients from 10−20 to 10−22 cm2 s−1, probably came from internal surfaces of micaceous clays, and began to be released at activity ratios below 3 × 10−4 to 6 × 10−4 M1/2 depending on soil type. The soils fell into three groups, broadly consistent with soil series, on their ability to release the second category of potassium.
|Number of pages||9|
|Journal||Journal of Soil Science|
|Publication status||Print publication - Dec 1979|