SIZE FRACTIONATION, DISSOLUTION ANALYSIS, AND INFRA-RED SPECTROSCOPY OF HUMUS COMPLEXES IN ANDO SOILS

Eight samples of Ando soil A₁ and buried A₁ horizons of different ages were fractionated into clay-, silt-, and sand-size separates, and the yields and carbon contents of these separates were determined. The clay-size separates were subjected to two series of successive extractions, 1) 0.1 M Na₄ P₂ O₇/2% Na₂ CO₃/0.5 M NaOH and 2) dithionite-citrate/2% Na₂ CO₃/0.5 M NaOH; and to difference infra-red spectroscopy for identification of the extracted constituents. The result indicated that humus evolves from forms with a very low complexing ability for Al and Fe into forms that complex Al and Fe in the A₁ horizon, and that humus further interacts with allophane-like constituents, allophane and imogolite in the buried A₁ horizon. These reactions between humus and inorganic constituents result in formation of silt- and sand-size aggregates which are stable to sonic wave treatment, but are broken down into finer particles upon boiling with H₂ O₂.