Abstract <p>The paper evaluates the effect of erosion processes on the agrochemical and microbiological properties of the soil in different seasons of the year. The objects of the study are agro-gray soil of varying degree of water erosion (noneroded, slightly eroded, and moderately eroded) and gray soil under woody forest plantations (south of Moscow oblast). It was found that the content of alkaline hydrolyzable nitrogen, exchangeable potassium, and mobile forms of phosphorus in the soil depend both on the degree of soil erosion and on seasonal fluctuations. Analyses of chemical composition of soil organic matter reveal that summer period is characterized by an increase in carboxylic, carbonyl and aromatic components in soil, while other periods, by an increase in carbohydrate fractions. In the agro-gray soil, bacterial and fungal biomass stocks ranged from 27 to 96 kg ha^‒1 and from 10 to 357 kg ha^‒1, respectively. Their dynamics is mainly associated with the erosion degree and to a lesser extent, with the season. An increase in the erosion degree is associated with a decrease in both fungal and bacterial biomass in the series of noneroded &gt; slightly eroded &gt; moderately eroded soils. Eroded soils exhibit, on average, a 50% depletion in bacterial biomass and a 59% depletion in fungal biomass compared to noneroded soils. In the gray soil, bacterial biomass and fungal biomass stocks varied seasonally from 43 to 107 kg ha^‒1 and from 171 to 621 kg ha^‒1, respectively. The gray soil under forest is characterized by a superior microbial pool compared to all agro-gray soil variants; additionally, it is characterized by a high content of both actinomycete and fungal mycelium. In the studied soils, the level of potential respiration (Substrate-Induced Respiration, SIR) exceeds the level of actual respiration (basal respiration, BR) by 2‒33 times. The most active microbial biomass response to the addition of glucose has been observed in moderately eroded soil in the spring and summer periods.</p>