ACTIVE ALUMINUM AND IRON AND PHOSPHATE ADSORPTION IN ANDO SOILS

The status of aluminum and iron in 18 Ando soil samples was analyzed by selective dissolution analyses using 0.1 M Na4P2O7, dithionite-citrate, and 0.15 M oxalate-oxalic acid as reagents. The results were correlated with the phosphorus adsorption from NaH2PO4and Na2HPO4solutions (≤0.2 M). A linear multiple regression analysis indicated that the reactivity of aluminum toward H2PO4−and HPO42−, expressed as the molar ratio of phosphorus to aluminum, is, respectively, 0.29 ± 0.05 and 0.28 ± 0.07 for aluminum bound with humus, 0.46 ± 0.18 and 0.30 ± 0.22 for aluminum in allophanelike constituents, and 0.10 ± 0.03 and 0.02 ± 0.04 for aluminum in allophane and imogolite. The corresponding figures are 0.61 ± 0.23 and 0.70 ± 0.30 for iron bound with humus. The reactivity of iron in iron oxides is not significant. The phosphorus adsorption in A1 horizons of Ando soils is governed by aluminum followed by iron both bound with humus, whereas that in buried A1 horizons is governed by aluminum in allophanelike constituents followed by aluminum bound with humus, and that in (B) and buried (B) horizons is governed by aluminum in allophanelike constituents, allophane and imogolite. © 1979 The Williams & Wilkins Co.