Seasonal and Multi-Year Dynamics of Soil Moisture in Gleyic Chernozems (the Oka–Don Lowland)

The observed climate changes and increasing groundwater levels in the forest-steppe region should be reflected in the water regime of meadow-chernozemic soils (Gleyic Chernozems). This article analyzes the seasonal dynamics of volumetric moisture content in a fallow Gleyic Chernozem (Siltic, Hyperhumic, Pachic) and two arable Gleyic Chernozems (Siltic, Aric, Hyperhumic, Pachic), as well as the level of groundwater in the Tokarevskii district of Tambov oblast during the period from fall 2022 to summer 2023. The obtained data are compared with regime observations of volumetric moisture content and groundwater levels in these soils performed in 1969–1971. The use of automated monitoring systems for the soil moisture content and groundwater levels has allowed continuous data collection on soil moistureand detailed tracking of seasonal changes. The fallow meadow-chernozemic soils is characterized by higher moisture levels compared to arable soils; the upper horizons of cultivated soils are characterized by a higher frequency of wetting–drying periods and a shorter continuous duration of these periods, which is confirmed both by moisture monitoring data and by the morphological features of the soils, such as the form of carbonate pedofeatures and the depth of their detection. During the observation period in 2022–2023, the meadow-chernozemic soils were relatively dry, despite the higher than normal annual precipitation. Wilting point moisture in the top 20-cm layer of cultivated soils was established from March 2023, and in the fallow soil, from the end of April 2023. Periods with the moisture content exceeding the field capacity within the 60-cm-thick upper soil layer were not observed during the entire observation period. The soils were drier than in the dry year of 1972, when the moisture content was less than the wilting point in the upper part of the profile from June to September. In the wet years of 1969–1970, the moisture content did not drop below the wilting point in the upper 20-cm layer throughout the observation period. The main reason for this difference in the moisture content is the change in the groundwater level: in 2022–2023, the groundwater level was more than 4 m deep, whereas in 1969 it did not go deeper than 2 m, and in 1971, deeper than 4 m. As a result, the soil’s uptake of moisture through capillary rise did not occur in 2022–2023, and the water regime of the meadow-chernozemic soils more closely resembled the water regime of typical chernozems (Haplic Chernozems).