PHOSPHATE SORPTION IN RELATION TO EXTRACTABLE IRON AND ALUMINUM IN SPODOSOLS

Phosphorus is an important plant nutrient and of concern from the environmental point of view. Numerous studies on the relationship between P sorption characteristics and other soil properties have been done; however, most of these studies do not include originally sorbed (oxalate-extractable) P (P(o)). Since P(o) accounts for 17 to 66% of the total sorption capacity (P(o) + X(m), where X(m) is the P sorption maximum) in 43 Spodosol samples from British Columbia, Canada, it should not be ignored in P sorption models. The good correlations between oxalate-extractable Fe and Al (Fe(o) + Al(o)) and P sorption parameters (P(o), X(m), or P(o) + X(m)) indicate amorphous Fe and Al oxides are the major P sorbents in the soils studied. Phosphorus sorption capacity is predictable from Al(o) and Fe(o) by two existing models. The relationship between organically complexed Al and P sorption parameters may be important in forest and soil management, since the organically complexed fraction is relatively easily altered if environmental factors or management practices change.