[Application of a mathematical model to describe the dissolution of phosphorite of Riecito in Venezuelan soils]
1995
Sanchez A, W.R. | Mohsin, M.
The direct application of a phosphate rock (PR) in acid soil may serve as a source of phosphorus for plants if it dissolves and liberates the P required by the crops. An incubation experiment was performed to determine the rate and extent of dissolution (A) of five Venezuelan phosphorites (Chiguara, Lobatera, Monte Fresco, Navay and Riecito) applied in an Uracoa Ultisol of the state of Monagas. Each PR showed distinct rate and extent of solubility and the Riecito phosphorite (RP) gave the highest value, therefore this PR was selected to to evaluate the effect of soil properties on its solubilization. The dissolution of the RP was determined by extracting soluble P with 0.5 NaOH following a prewash with 1 M NaCl. The value of P extrated at different periods, during 90 days from seven soils incubated with the RP fitted very well (R2 80 percentage) in the equation of Mackay et al: y = A(1-e-ex), where y=amount of RP dissolved at time x; A=extent of dissolution or asymptote of the dissolution curve, and c=curvature coefficient. A varied markedly from one soil to another and c was independent for most of the soils, excepting two. The equation for calculating the value of A was determined by multiple regresion analysis with the soil properties like: exchangeable calcium, cation exchange capacity, calcium saturation, available phosphorus and phosphorus sorption capacity, that influenced most in the dissolution of the RP. Making different combinations with these soil parameters produced different equations for A, with a range of variation (R2) of 67,3 to 87,5%, according to the population of soils selected. This reconfirmed that the dissolution of a PR in the soil depends on the activities of the calcium (r=-0.854** ) and phosphate (r=-0.833** ) ions in the soil solution, among others.
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