Soluble Organic Matter in Soils of the Rostov Agglomeration

Specific features of humus accumulation and migration of water-soluble organic matter (WSOM) extracted by cold and hot distilled water in soil profiles were studied. The organic carbon content was determined on a TOC-L CPN Shimadzu carbon analyzer with the solid sample combustion. The nitrogen content was determined on an Elementar Analyze GmbH (Hanau, Germany). Samples from Calcic Chernozems (Pachic) under natural steppe vegetation, their analogues under artificial tree plantations, urbostratozems (Urbic Technosols (Mollic), Urbic Technosols, and Calcic Chernozems (Technic) were studied. The WSOM fractions constituted a small part of the total soil organic matter (SOM); their content did not exceed 0.14% of the soil mass, or about 4% of the total soil organic carbon (Cₒᵣg). For urbic horizons of anthropogenic soils, these values were much lower: 0.04% and 2.0%, respectively. The migration of organic matter along the soil profile was better pronounced in soils developing under forest vegetation. There was a slight accumulation of SOM at the level of carbonate barrier. Distribution patterns of WSOM in the profiles differed for anthropogenically transformed and natural soils. In the anthropogenically transformed layers, WSOM distribution displayed a chaotic pattern with a smooth decrease down the profiled in the underlying Chernozem layers. Long-term conservation of the soil under impermeable or semipermeable covering layers favored the absence of WSOM accumulation in the lower part of the anthropogenic soil thickness at the level of carbonate barrier. The WSOM fractions were rich in nitrogen with its maximum content in the WSOM extracted by hot water from the lower soil horizons. The low extinction coefficients of WSOM in these horizons indicated the presence of low molecular-weight substances of phenolic nature.