AVAILABILITY OF POTASSIUM TO RYEGRASS FROM SCOTTISH SOILS II. UPTAKE OF INITIALLY NON-EXCHANGEABLE POTASSIUM |
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| Authors: | A H SINCLAIR |
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| Institution: | (Department of Soil Fertility, The Macaulay Institute for Soil Research, Craigie buckler, Aberdeen, AB9 2QJ, Scotland.) |
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| Abstract: | 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. |
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