EFFECTS OF PHOSPHORUS CONCENTRATION AND pH ON PHOSPHATE RETENTION BY ACTIVE ALUMINUM AND IRON OF ANDO SOILS
1981
GUNJIGAKE, NORIAKI | Wada, Kōji
We measured phosphate retention by 18 Ando soil samples at different pH values (4 to 8.5) and phosphorus concentrations (10 to 2 M). A general regression equation held for each soil: log Y = α pH + β log [C] + c, where Y = phosphorus retention and [C] = phosphorus concentration. By multiple regression analysis, the Y values were correlated with the status of aluminum and iron analyzed by selective dissolution using pyrophosphate, dithionite-citrate, and oxalate-oxalic acid as reagents. Aluminum bound with humus, Alpyr, reacted with phosphate depending little on pH and markedly on phosphorus concentration, whereas aluminum and iron in allophane, (Al + Fe)oxa, depending markedly on pH and moderately on phosphorus concentration. Aluminum and iron in allophanelike constituents (Al + Fe)dit-pyr showed features similar to aluminum bound with humus. The molar reactivity of aluminum and iron toward phosphate (P/Al or Fe) at 0.5 M increased in the order: (Al + Fe)dit-pyr (0.3) < (Al + Fe)oxa (0.4) < Alpyr (0.5) < Fepyr (0.8) at pH 5.0, and (Al + Fe)oxa (<0.1) < (Al + Fe)dit-pyr (0.3) < Fepyr (0.5) < Alpyr (0.6) at pH 8.0.
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