Factors of winter moisture movement in arable soils of the Ishim steppe

Based on the materials of long-term field observations in the southern regions of the Omsk region, the influence of the main factors on the winter movement of moisture in arable soils of the Ishim steppe was traced. The penetration depth of 0 °С determines the lower boundary and vertical thickness of the moisture freezing layer. The distance between its lower edge and the penetration depth of 0 °С is 20–40 cm. The penetration depth of 0 °С is predetermined by the air temperature and the thickness of the snow cover and reaches 170–240 cm. The forms of moisture dominant in the soil are associated with the granulometric composition. Film moisture prevails in the heavy loamy, highly silty soil-ground strata of the Ishim steppe. The content of capillary-backed and free gravitational water does not exceed 6% of the soil volume at full moisture capacity, which determines the small volume of moisture freezing (up to 50 mm). Thermogradient migration of moisture is determined by field methods in highly moistened soil-ground strata. High humidity of the soils and rocks of the Ishim steppe is associated with their granulometric composition and the close occurrence of groundwater. If in the second ten days of October groundwater is recorded at a depth of less than 3 m, the layer of moisture freezing at the end of March is noted in the depth range between 40–80 and 160–200 cm, the volume of cryogenic accumulation is 30–50 mm, including in the upper meter layer – 10–25 mm. If groundwater is detected at a depth of more than 3 m in the autumn, the freezing layer is fixed at 80 to 160–200 cm, the moisture gain in it is 15–30 mm, in the 0–100 cm layer the moisture content does not change. The role of cryogenic accumulation in replenishing the post-vegetation moisture deficit in the root layer of spring grains is modest. This process is significant for the formation of conditions for anaerobiosis and the development of modern hydromorphism in the lower soil horizons and in the subsoil strata.