On the basis of experimental and literary data the assessment of humus state of arable layer of differently cultivated typical agrarian-grey heavy loamy non-eroidated soils of the center of the Non-Black Earth zone of Russia was carried out. The gradations of humus content corresponding to the different level of soil fertility were determined. The optimal interval of humus content is calculated on the basis of its minimal value in non-erodized agrarian soils of the region and optimal limits of transforming organic matter. It is shown that at development of grey soils under forest in arable horizonThe content of humus, fulvic acids, mobile humic acids, extracted 0.1 n. NaOH, decreases, and the amount of humic acids associated with Ca sharply increases with the increase of their optical density and ratio to mobile humic acids to the level in agronomic black soil. Further domestication of agrarian soils on the background of systematic application of increased doses of organic fertilizers, along with increasing the content of humus, there are reverse changes in the ratio of these fractions of humic acids. At the same time, the optical density of humic acids associated with clay minerals decreases significantly, which indicates the processes of their renewal and enrichment by aliphatic structures. Criteria of difference between agrarian soils and podzolic soils and agronomic chernozems by quality of humus in arable horizon are discussed.