Assessment of the humus content in arable soils of Russia

The assessment of the humus content in the mineral soils of Russia based on theoretical, calculated, and expert approaches is given. A review and analysis of the gradations according to the humus content elaborated at the Dokuchaev Soil Science Institute (1977, 1985, 1997, 2001, 2003, and 2004) and by Orlov with coauthors (1978 and 2004) are presented. A theoretical substantiation is given, and an inventory of the soils of Russia qualified by their humus content where the starting point is the minimal humus content is suggested. The objective intervals of the schedule of the humus content are based on the permissible discrepancy of the results obtained by different laboratories. A notion of the global assessment covering a wide spectrum of soils and reflecting the difference between the soil types according to the humus content is introduced, and a differentiated assessment characterizing the differences within the type (subtype) of soils assessed using this parameter is given. The methodological approaches for the determination of the minimally permissible, optimal, and maximally allowable humus contents in the plow horizons are described.