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A simple model for predicting the rates of dissolution of sparingly soluble calcium phosphates in soil
Author(s) -
KIRK G. J. D.,
NYE P. H.
Publication year - 1986
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.1365-2389.1986.tb00386.x
Subject(s) - dissolution , phosphate , calcium , chemistry , phosphorite , volume (thermodynamics) , rhizosphere , mineralogy , particle (ecology) , inorganic chemistry , geology , biochemistry , thermodynamics , organic chemistry , paleontology , physics , oceanography , bacteria
SUMMARY The effect of non‐uniform distribution of particles in the soil on the rate of dissolution of calcium phosphate particles was investigated, using a negative binomial distribution to describe the degree of clumping of the particles. A randomly distributed sample dissolved about 10% more slowly than a regularly distributed one. For a degree of clumping in which the sum of the spherical volumes influenced by particles was about 10% of the whole soil volume, the predicted rate of dissolution was reduced by about 85%. The effect of a range of particle sizes in the applied material was also investigated. Typical grades of commercial rock phosphate contain a high proportion of fine particles, resulting in a rapid initial rate of dissolution of the applied material, but the rate trails off as the small particles are exhausted. The effect of the presence of plant roots was also considered, using average root characteristics and assuming the root effects to be spread over the whole soil volume. The rate of calcium phosphate dissolution was increased by root uptake of dissolved phosphate ions, by an amount depending on the rooting density and the rate of calcium phosphate application, and by secretion of acid by the roots. In many circumstances where rock phosphates are applied as fertilizers, plants are likely to be rhizosphere acidifiers; sufficient acid may be secreted to render rock phosphates soluble where they would other‐wise be insoluble. Generally, calcium uptake will not greatly affect the rate of calcium phosphate dissolution.