Characteristics of Buried Humic Horizons at the Shiiji Archaeological Pits

Abstract

As a part of the studies on the changes in the properties of soil organic matter with the time after burial, humus-clay complexes were separated from the surface and buried humic horizons derived from volcanic ash deposits whose age ranged from the present time to about 26,000 years B.P. Amorphous aluminium constituents were separated into fractions from the humus-clay complexes by using the selective dissolution treatments. 1) The amorphous aluminium constituents separated by the selective dissolution treatments were designated as follows: the aluminium constituents dissolved by formate treatment were designated as the hydroxyl Al polymer-Al2O3 fraction, those dissolved by citrate-dithionite-bicarbonate (CBD) treatment minus the formate soluble fraction as the humate-Al2O3 fraction, and those dissolved by oxalate treatment minus the CBD soluble fraction as the allophane-Al2O3 fraction. Moreover, the amorphous aluminium constituents designated as the humate-Al2O3 fraction were subdivided into two groups: the humate (1)-Al2O3 group which included the constituents dissolved by sodium pyrophosphate solution (SPP) treatment minus those dissolved by the formate treatment, and the humate (2)-Al2O3 group which consisted of the constituents dissolved by the CBD treatment minus those dissolved by the SPP treatment. 2) The changes in the hydroxy Al polymer-Al2O3 contents with time were not significant. The humate-Al2O3 contents tended to decrease in the older horizons, while the allophane-Al2O3 contents increased in the older horizons. The humate (1)-Al2O3. contents decreased in the older horizons, while the humate (2)-Al2O3 contents increased in the older horizons. The humate-Al2O3 contents showed a very significant positive lineal correlation with the carbon contents of the humus-clay complexes (r=0.980).