CHANGES IN THE TEXTURE AND EXCHANGE PROPERTIES OF SKELETAL QUARRY DETRITUS UNDER FOREST DURING THIRTY YEARS

Abstract

Areas of former open-cast oil-shale mines afforested about 30 years ago were studied at Sirgala, NE Estonia. Synchronously with the development of high productivity pine stands, a rapid progress of Calcaric Regosol has taken place on pure skeletal (450 -650 g kg -1 of skeleton) quarry detritus. Organic carbon of the R 2O3-humic-fulvic forest humus of litter and root origin amounts to 28 ± 6 g kg -1 in the epipedon formed and to 13 ± 3 g kg -1 in the transitional AC-horizon. The proportion of humus compounds bound with clay and immobile sesquioxides is also significant. Forest humus is active and the soluble fractions make up 60-80% of total organic carbon. Interactions between the formed humus and the mineral stratum of detritus have resulted in the weathering of stone, gravel, and sand fractions and in the accumulation of clay in the epipe don and of silt in the transitional horizon. Subsequent physical and further chemical weathering, progressing in depth, are characteristic of any fraction. The territorial (site) variability of changes in texture is lower than in the composition of organic pedogenetic agents. Ca 2+ forms more than 80% of base exchangeable capacity, the proportion of Mg 2+ being highly variable. Humus colloids are prevalent