The characteristic of humus qualitative compo-sition in mountain forest-steppe of Orkhon-Selenga midland (Northern Mongolia) was shown. The study area was situated on the ridge Delger Khan at alti-tudes of 700-800 m above sea level within the model range "Shaamar". The feature of the territory was the prevalence of sandy-loamy arrays. Plant cover was characterized by the alternation of sparse pine and birch forests with mountain-meadow vegetation, and meadow steppe on the slopes of the northern and eastern exposures and dry steppe with unproductive xerophytic herbage. The diversity of soils was represented by light dif-ferentiated soil types of carbonate-accumulative and organic-accumulative departments of postlithogenic trunk. Fine sand and silt fractions with low clay content dominated in the texture. The humus content in the soils of carbonate-accumulative department was low and very low, in the soils of organic-accumulative department was medium and low. The study of humus fractional composition revealed significant proportion of non-hydrolyzable residue. Automorphic soils were of fulvate-humate humus type that is characteristic of steppe soils. The ratio of carbone of humic (HA) and fulvic (FA) acids in soil was 0.90-0.73. The profile distribution of humus content was sharply decreasing. Fraction associated with calcium and strongly bound fractions predominated in the com-position of humic acids. Free humic acid fraction was of the lowest value. Fulvic acids (FA) were mostly represented by FA-2 and FA-3 fractions. Soil evolution had steppe type direction. The pro-cess of humus-formation in soils of trans-accumulative positions was of meadow-steppe type. Profile distribution of humus was gradually decreasing. The proportion of humic acids in hu-mus increased. Humus type was fulvate-humate. There was high content of brown humic acids in the upper layer of forest that is the feature of the forest soil-forming process. The comparative analysis of the data showed that the studied area was the zone of contact of semi-arid steppe and semi-humid forest conditions. The soils of forest-steppe transition zone were predominantly accumulative, neutral alkali, saturated soil formation and devel-oped both in steppe, meadow steppe and forest-steppe directions.
mountain forest-steppe, soil, hu-mus, group and fractional structure
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