Sorption of phosphorus by some surface soils from Quebec in relation to their properties

Abstract

Surface horizons from Podzolic and Gleysolic soils were collected in various parts of the province of Quebec, Canada, and equilibrated with various amounts of KH₂PO₄ in 0.01 M CaCl₂ for 48 hours. P sorption data conformed to the linear form of the Langmuir and Freundlich equations. P solubility isotherms showed evidence of hydroxyapatite formation in most samples studied, whereas equilibration solutions of only few samples were saturated with respect to either dicalcium phoshate dihydrate or octocalcium phosphate. These reaction products were associated to soil pH and levels of added phosphate. The average values of the Langmuir sorption maximum for these studied Gleysolic and Podzolic samples were 763 and 1096 μg/g respectively. These values were higher than those obtained by the segmented and modified Freundlich models.

Relationships between the soil characteristics and P sorption parameters were evaluated by regression analysis. Among all variables, oxalate‐extractable Fe plus Al content of the Podzolic samples and the ratio of oxalate—extractable Al to clay of the Gleysolic samples gave the best significant correlation coefficients. Furthermore, soil pH and various ratios such as pyrophosphate‐extractable Fe and Al, oxalate‐extractable Fe and organic matter to clay were found to be significantly correlated only with the P sorption parameters of the Gleysolic samples.

Key words:

• Podzolic and Gleysolic soils
• Sorption maxima
• solubility isotherms
• maximum buffer capacity
• P sorption index