A new adsorption isotherm for phosphate in soil

TLDR: The inclusion of a square root term in the Langmuir equation could be taken to imply that the soil will adsorb a little phosphate firmly, a slightly greater amount of phosphate less firmly, and so on until a limiting value is reached when all the components of the phosphate adsorption system are saturated.

Abstract: Summary Phosphate adsorption data for 24 soils showed that although the Langmuir equation gave a good fit, there was significant curvature. Of the alternative equations examined, that of Freundlich provided a better description than that of Langmuir in 22 soils, but the best fit, accounting for more than 99·8 per cent of the variation in phosphate adsorption, was given by introducing a square-root term: where y= adsorbed phosphate, c= equilibrium concentration of phosphate in solution, B, A, and D are constants. The phosphate adsorption maximum, obtained from I/B, gave values in the range 325 to 1427 μg P/g soil which were 1·39 to 2·40 times those obtained from the Langmuir equation. The inclusion of a square-root term in the Langmuir equation could be taken to imply that the soil will adsorb a little phosphate firmly, a slightly greater amount of phosphate less firmly, and so on until a limiting value is reached when all the components of the phosphate adsorption system are saturated.