Use of the Freundlich sorption equation for evaluating the phosphate requirements of arid zone soils
1988
Berigari, M.S. (Scientific Research Council, Baghdad (Iraq))
Simple, quick and verified laboratory tests bear some obvious merits over the long range and expensive field trials to assess phosphate requirements of soils. Samples from typical soils of Iraq were equilibrated with a wide range of phosphate (P) concentrations (0-30 mg P/L) at 1:20 soil to solution ratio. Phosphate in the supernatant solution was measured photometrically in order to determine by difference the quantity of soil adsorbed -P. The data conformed to the linear plots of the Freundlich, Langmuir and Temkin equations at highly significant positive correlations. Superior fit of the data, however, was observed with the Freundlich equation which is simple in form and subject to rigorous derivation with more realistic assumptions. The estimated P requirements of most soils ranged between 32-52 mg P/kg soil when obtained from normal isotherms which agreed closely with the values obtained from application of the Freundlich equation. Thus, to estimate P requirement of a given soil for optimum crop production only two points sorption data are needed where linear Freundlich plot can be applied
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