ABSTRACT Aware of the environmental and agronomic benefits and disadvantages of phosphate (H 2 P) retention in soils, we hypothesized that the adsorption of H 2 P by the soil organic matter (SOM) is intensified by cation bridges and resulting ternary structures SOM‐cation‐H 2 P. The objective was to evaluate H 2 P adsorption as affected by the addition of different multivalent cations and by SOM characteristics, supposedly by formed ternary structures SOM‐cation‐H 2 P. The study was carried out with six samples of subtropical Histosols identified as 2B, 2C, 3B, 3C, 4B and 4D collected at 0–0.05 m and treated with HF to concentrate SOM. The pH of treated samples was standardized to 5.0 and cation exchange capacities (CEC) of samples were saturated with Ca 2+ , Al 3+ , La 3+ and Ce 4+ to induce cation bridges. We used data of analytical pyrolysis of SOM to relate SOM characteristics with our data of cation bridges and H 2 P adsorption. After HF treatment, the TOC content increased, for example, by 84% in sample 3B (to 460 g kg −1 ) and 186% in 4B (to 458 g kg −1 ). H 2 P adsorption on SOM in control sample without cation addition ranged from 121 to 556 mg P kg −1 and was attributed to the direct formation of the binary structures SOM(NH 3 + )‐H 2 P. Multivalent cations had two opposite effects regarding H 2 P adsorption, one positive by formation of the ternary structures SOM‐cation‐H 2 P, and another negative by flocculation of organic colloids and occlusion of adsorption sites, making them unavailable for H 2 P adsorption. The tetravalent cation Ce 4+ was the most efficient to form the ternary structures SOM‐cation‐H 2 P, associating even with the less likely protonated phenol (OH). The cation Al 3+ , predominant in acidic soils, even with the strong hydrolysis reaction at pH 5.0, was more efficient than La 3+ in the formation of ternary structures SOM‐cation‐H 2 P.
Gavelaki et al. (Thu,) studied this question.