ORGANIC-MATTER IN VOLCANIC SOILS IN CHILE - CHEMICAL AND BIOCHEMICAL-CHARACTERIZATION

Determinations were made of total soil organic matter (SOM), stable an d labile organic fractions, biomass carbon (C), and chemical compositi on of several humus-soil-fractions in chilean volcanic soils, Andosols and Ultisols. Their physico-chemical Properties and humification degr ee at different stages in edaphic evolution were also assessed. In add ition, organic matter models were obtained by chemical and biological syntheses and the structures and properties of natural and synthetic h umic materials were compared with SOM. Results indicate that Andosols have higher SOM levels than Ultisols, but the fraction distribution in the latter suggests a shift of the more stable fractions to the more labile ones. Moreover, contents of humines, and humic and fulvic acids suggest that Chilean volcanic soil SOM is highly humified. On the oth er hand, among the SOM labile fractions, carbohydrate and biomass are about 15% of the SOM which are one of the most important fractions in soil fertility.