A New Adsorption Isotherm for Phosphate in Soil

This is the authors' abstract. We don't add key points for this paper.

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: image 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.