Object – features of the humus state and transformation of the organic matter in alluvial-meadow soils on the example of Kharkov region. Purpose – show the specificity of the organic matter transformation and reveal the features of the humus state in alluvial-meadow soils of the Left-bank Forest-Steppe and North Steppe zones of Ukraine (on the example of Kharkov region) in order to improve ways to ecological and safe use of flood-plain lands, which are directed to the stabilization of humus reserve as well as neutralization of degradation processes and preserving meadow soils. Methods – field, laboratory and model, laboratory and analytical, mathematical statistics, computational and comparative. Theoretical results – features of humus complex formation and patterns of transformation of organic compounds (humus), effected by specific floodplain formation conditions, in alluvial-meadow soils of the Left-bank Forest-Steppe and North Steppe zones of Ukraine (on the example of Kharkov region) were shown. It was also highlighted carbon-sequestration ability of alluvial-meadow soils and mineralization ability of humus and calculated humus content and humus reserve in these soils. Practical results – improve scientific approaches to rational and ecologically safe use of floodplain soils, directed to optimization their humus state and saving carbon reservoir, and which consist in following land adaptive structure of land use, keeping meadow soils entirely as grasslands and pastures, implementing the system of line and phytoameliorative grassland and developing actions for decreasing degradation processes. Results of the research were included into database of the Ukrainian national map of soil Carbon reserve as a part of Global smart map of organic Carbon for 0-30 sm layer (GSP FAO UNO). Novelty – at first time patterns of humus reserve formation and features of organic compounds transformation in alluvial-meadow soils of the Left-Bank Forest-Steppe and North Steppe zones of Ukraine (on the example of Kharkov region) were determined, effected by the specificity of floodplain soil formation (humus-accumulative type, sedimentation of allochthonous material, high level content of sesquioxides and moisture mode) and also scientific approaches to balanced use, directed to the stabilization of humus reserve and neutralization of degradation processes of meadow-soils, were improved. It was proved that humus state of the alluvial-meadow soils, in contrast to automorphic soils, is characterized by lacking profile distribution of humus, ecological sensitivity of humus complex, fulvic-humate, humate or pure humate type of humus, and contrast percentage of nitrogen. At first time, the relationship between carbon-sequestration ability of alluvial-meadow soils and the level of humification of alluvial-delluvial sediments was described. Degree of application – the results of the research were used in study process of master degree in KhNAU named after V. V. Dokuchaev for «Agronomy» specialty (201) while teaching disciplines of EPP “Agrochemistry and Soil Science” and “Soils scientific assessment” and were implemented on the lands of LLC “Karat”, Novovodolazhskiy district, Kharkov region on the area of 10 hа. The field ‒ is agriculture.
