Structural Characteristics of Reddish Soils from the North-eastern Part of Sofia Field

Abstract

The study presents basic structural characteristics of ten profiles of Reddish soils (Haplic Leptosols, Haplic Cambisol, Haplic and Cutanic Luvisols with Chromic or Rhodic characteristics) of different formation stages and parent materials, located in North-eastern part of Sofia field. Type, size distribution and water stability of soil aggregates were determined and explained taking into account textural characteristics, organic matter contents and other factors influencing soil structure formation. Soil density and total porosity were also used for assessing physical status along the soil profiles.
The humic horizons of the most of studied soils under pristine (grassland) conditions are well structured and with high water stability of soil aggregates. The main role for aggregates formation play the high organic matter content and most probably the Fe-(hydr)oxides in case of coarse textured Haplic Leptosols. The water stability of soil aggregates is lower in the surface horizon of Haplic Cambisol due to low content of organic matter and location of the profile on the South slope. The cultivated Haplic Luvisol is characterized with the lowest water stability of soil aggregates. Well pronounced alteration of the structural characteristics in illuvial horizons is observed in the studied Haplic and Cutanic Luvisols. The type of structure is changed from granular in A horizon to blocky in Bt. The illuvial horizons are characterized with low water stability of aggregates, and hence high compaction, which impede the transmission of water. The occurrence of Mn concretions in Bt horizons corroborates the suggestion for frequently occurrence of waterlogging. Exception is Haplic Luvisol (Clayic, Rhodic) with the highest Fe content along the soil profile. The structure of the illuvial horizon ensures enough content large pores for water transmission.