Aluminum diffusion in oxisols as influenced by soil water matric potential, pH, lime, gypsum, potassium chloride, and calcium phosphate

Plant root exposure to soil aluminum (Al) depends on the soil solution Al c oncentration and transport to the root by diffusion. Changes in Al diffusiv e flux for two Oxisols was measured under Laboratory conditions as a functi on of pH, water matric potential, and applications of gypsum, potassium chl oride, and calcium phosphate. Double-faced cat:ion exchange resin sheets se rved as sinks for Al transported during 10-day incubations through chambers containing 314 cm(3) of soil. Across a range of soil pH values from 4.5 to 5.5, maximum diffusive flux of Al occurred at pH values of 4.7-4.8 in both soils and corresponded to increases of 2.2-3.0% relative to the unlimed tr eatment. Between pH values of 4.7-4.8 and 5.4, diffusive flux of Al decreas ed by 38 and 46% in the two Oxisols. Diffusive flux of Al decreased by 16-2 0% for the two Oxisols as soil water potentials decreased from -10 to -200 kPa. Magnitude of the reductions in diffusive flux of Al with decreasing so il water potential were less than those reported for diffusive flux of phos phorus (P) in prior investigations. Diffusive flux of Al increased by as mu ch as 4-fold with additions of CaSO4 and KCI, which increased the soil solu tion Al concentration. Additions of 400 mg P dm(-3) of soil had no effect o n Al diffusion in either Oxisol.