FRACTIONAL COMPOSITION OF HUMUS IN SELECTED FOREST SOILS IN THE KARKONOSZE MOUNTAINS

Abstract

This paper describes the fractions of humus compounds present in the organic and mineral horizons of the forest soils in the area of the Karkonosze Mountains. Soil profiles that represented the mountain Podzols and Dystric Cambisol were located on the northern slope along an altitude gradient from 890 to 1255 m a.s.l. Two soils were located under the spruce forest, and one in the subalpine meadow. Soil samples were taken both from the surface organic layers (the ectohumus layer) and from the mineral horizons. Fractionation of humus compounds was made using the modified Turin method. The soils had the texture of loamy sand and sandy loam, an acidic or strongly acidic reaction, low base saturation, and the predomination of aluminum among exchangeable cations. A significant increase in the fulvic fraction (Ia) with depth in the soil profiles was observed that confirmed the high mobility of this fraction in the acid mountain soils, higher in the forest soils, and lower in the meadow soils. The content of fraction I decreased generally with depth in the soil profile; however, a secondary increase was observed in an illuvial Bh horizon of the Podzols. Fulvic acids predominated over the humic acids and this predominance increased with depth in the soil profile. The ratio of the humic to the fulvic acids in fraction I in the ectohumus horizons was influenced by the composition of a biomass inflow. TheCHA:CFA ratio had the highest values under a spruce forest compared to a mixed stand and a subalpine meadow. In the surface horizons of the forest soils, a predominance of humic over fulvic acids was always observed, while in the subalpine meadow soils, the fulvic acids predominated over the humic acids in all soil horizons. Based on this study, it can be stated that the vegetation type and the dominant soil-forming process rather than simply climate factors influence the fractional composition of humus in the mountain soils of the Karkonosze Mountains.