Spatial Variability of Phosphate Adsorption Parameters
- S. E. A. T. M. van der Zee *,
- M. M. Nederlof,
- W. H. van Riemsdijk and
- F. A. M. de Haan
Reversible phosphate (designated P) adsorption for acid soils with a narrow pH range is described with the Langmuir kinetics equation. Using a combination of two experimental desorption techniques, i.e., desorption in water and desorption in the presence of an “infinite” sink for P, respectively, the adsorption maximum (Qm) and the adsorption constant (K) were assessed for soils (pre-)saturated with P. The adsorption maximum was proportional with the sum of oxalate-extractable Fe and Al (ME) (i.e., Qm ≈ 0.135 ME), for topsoil samples from a field and a watershed. The K values found for the field and for the watershed samples were in the same order of magnitude (K = 15−25 L mmoL−1). The adsorption maximum and the adsorption constant, as well as the amounts of P desorbed, were spatial variates. The distributions were fitted to the normal as well as the lognormal distribution at the significance level of 0.05, using the Kolmogorov-Smirnov test statistic.
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