Spatial Variability of Phosphate Adsorption Parameters

Abstract

Abstract 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 ( Q m ) 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., Q m ≈ 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.