Distribution of Humus Substances Between Clay Particles of Different Peptization Level in the Meadow Soils of the Middle Priamurje, Russia

Abstract

Soil clay (particles <2 μm) was sequentially divided into water-peptizable clay (WPC) and aggregated clay (AC) subfractions according to their ability to peptizate in water. The content of humic acids (HA), fulvic acids (FA), and humins was estimated in both subfractions. The studied soil was the meadow podbel (planosol in the FAO system), periodically over-moistured with atmosphere precipitation. The soil profile revealed well-marked genetic horizons. Specifics of the quantitative content of WPC and AC in the major horizons of this soil were determined. All fractions of HA and FA are present in WPC in small quantities. The most amounts of humus substances were associated with AC and sometimes with a non-peptizable soil residual (sum of particles >2 μm). The results of the revaluation of data of group and fraction composition of humus in WPC and AC considering the content of WPC and AC in soil showed that over 70% of total content of I fraction of HA and FA are concentrated in AC of the humus horizon. This indicates its defining role in organomineral interactions and processes of soil material aggregation in the humus horizon of the meadow podbel.