Aluminum Release Rates from Allophanic and Nonallophanic Andosols

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Aluminum release rates were studied for subsoil horizons of allophanic and nonallophanic Andosols and for imogolite gel films. Release rates were determined using a stirred, flow-through reaction vessel with a 10^<-3> _M acetate buffer adjusted to pH 3.3, 3.8, or 4.2. To determine the sources of dissolved Al, soils were pretreated with KCl, Na-pyrophosphate, citrate-bicarbonate-dithionite, and acid oxalate to remove various solid-phase pools of active Al. Rates of Al release for imogolite gel films during the first minute of reaction ranged from 74.8 nmol/g/s at pH 4.2 to 113.3 nmol/g/s at pH 3.3. Rates of Al release for nonallophanic Andosols were greater than for allophanic Andosols due to the rapid release of exchangeable Al from nonallophanic Andosols. Aluminum release rates showed fractional order H^+ -dependence ranging from 0.23 to 0.54. The primary source of dissolved Al in allophanic Andosols, exchangeable Al and Al-humus complexes were the primary sources of dissolved Al. Treatment with KCI increased Al release rates for allophanic Andosols, possibly due to precipitation of polymeric-Al on soil surfaces. Iron oxyhydroxide coatings substantially attenuated Al release rates from allophne and imogolite in allophanic Andosols.
社団法人日本土壌肥料学会の論文