THE RELATIVE IMPORTANCE OF OXALATE AND PYROPHOSPHATE EXTRACTABLE ALUMINUM TO THE ACIDIC LEACHING OF ALUMINUM IN PODZOL-B HORIZONS FROM THE PRECAMBRIAN SHIELD, ONTARIO, CANADA

Four Bf and one Bhf Podzol horizon samples from the Precambrian Shield, Ontario, Canada were leached with pH 3 solutions in three different experiments to determine which soil aluminum fraction was primarily responsible for the aluminum leached into solution. For the Bf horizons, it was primarily the oxalate-extractable aluminum fraction (corrected for pyrophosphate, Al-o-Al-p); for the Bhf horizon it was equally the pyrophosphate (Al-p) and Al-o-Al-p. A comparison with other studies suggests that when the ratio (Al-o-Al-p)/Al-p is above 0.3-0.7, the oxalate-extractable fraction will be most important, and at lower ratios Is the pyrophosphate fraction becomes most important. The pattern of fluoride leaching in these experiments suggests that F was concentrated primarily on the surface of the amorphous aluminum fraction.