Humus condition of brownish-podzolic soils of the Pregorganian Precarpathians

Abstract

The indicators of humus condition reflect not only the productivity of soils, but also the features of the genesis, intensity and direction of soil-forming processes. It was found that the brownish-podzolic soils of the Pregorganian Precarpathian region are characterized by a low content of humus (1 36-3.7%) within the NE gl horizon, and in the lower horizons its content decreases sharply. Profile distribution of humus is determined as regressive-accumulative type, which is typical for most soils with elluvial-illuvial type of profile. The content of humus in the silty fraction of the studied soils is 1.5-2.0 times higher in comparison with the fine soil, and within I (e) m gl of the horizon the accumulation of humus is established, which is due to the lessivage process. Brown-podzolic soils are characterized by fulvate type of humus (C ha: C fa = 0.2-0.5). The movement of fulvic acids within the profile, especially organo-mineral colloids, is caused by the lessivage process. Among fulvic acids, the fraction connected with the mineral part (FC-3) has the highest content, which increases with the depth from 17.6 to 35.1%. The enhance in the content of this fraction with depth is primarily due to the ability to migrate within the profile. It can cause both the movement of fulvic acids deep into the profile with their sorption on peptizing colloids, and the joint movement of organo-mineral peptized colloids in the profile. The highest level of humification (28.10–28.75%) have upper humus-elluvial horizons, because they create the best conditions for the intensive activity of microorganisms. The humus content in clay cutans is 1.5 times higher than in the contained illuvial horizon, which is caused by lessivage and clay granulometric distribution. The humus content in the nodules is lower (0.26%) in comparison with the contained horizon. The results of the optical density analysis indicate a decrease in the extinction index from NE g1 to I (e) m gl of the horizon, which correlates with the indicators of the profile distribution of humic acids, the total content of which decreases with the depth. Such characteristics of humus composition indicate the genetic affinity with brown forest soils.