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AVAILABILITY OF POTASSIUM TO RYEGRASS FROM SCOTTISH SOILS II. UPTAKE OF INITIALLY NON‐EXCHANGEABLE POTASSIUM
Author(s) -
SINCLAIR A. H.
Publication year - 1979
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1979.tb01026.x
Subject(s) - potassium , soil water , chemistry , diffusion , desorption , zoology , environmental chemistry , mineralogy , soil science , geology , adsorption , biology , thermodynamics , physics , organic chemistry
Summary 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, AR K = a K /√ a C a , Mg at which K was first taken up from non‐exchangeable sources varied from 3 × 10 −3 to 8 × 10 −3 M 1/2 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 cm 2 s −1 for four soils. The second category gave diffusion coefficients from 10 −20 to 10 −22 cm 2 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 M 1/2 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.