Molecular weights of humic acids in podzol and ferrallitic soils of the savannas of French Guyana and their evolution related to soil moisture

Abstract

Different molecular weight fractions of humic acids from A1 horizons of ferrallitic and podzol soils have been separated by means of gel filtration, after extraction with 0·l N sodium pyrophosphate. Soil sampling was related to seasonal changes in climatic periods (drying, dry. re wetting, saturation). Results are compared to those of electrophoretic analysis. Among the fractions, some are permanent in the soil extract and other appear or disappear according to the climatic variations. A fraction with a molecular weight of 3000 seems to be one of the characteristics of dynamic phases in humus changes in podzol soils and can be related to soil moisture at the time of sampling.