A comparison of the compositions and properties of natural and laboratory-prepared humified organic matter

Abstract

Some properties of the soluble decomposition products of aerobically incubated plant material are compared with those of organic matter extracted from a top-soil. Expressed as organic C, roughly half the soluble organic matter in the laboratory preparation dialyses through Visking cellulose, against water. The dark-coloured larger molecular weight fraction of the laboratory preparation strongly resembles natural humose matter, and the amino acid compositions of the two hydrolysed humic acids agree quite closely. It seems that the laboratory preparation has the properties to be expected of a juvenile form of natural soil organic matter. The non-dialysable organic matter, both natural and laboratory-prepared, is sorbed on soil colloids, but as very little of the dialysable material is sorbed, this fraction presumably tends to be leached from the soil profile. With kaolinite, air-drying the treated clay caused hysteresis between the sorption and desorption of both forms of organic matter; with synthetic goethite the hysteresis exhibited by the undried preparation was not affected by air-drying.