Characteristics of hydrothermal mode of soils of Predsalairye during cold period (within Bugotac Hills)

Specific character of development of erosive processes on chernozems of Western Siberia, according to systematic researches, is caused generally by climatic and soil and physical conditions of formation of temperature and water modes of soils during the cold period. For the purpose of determination of features of temperature and moist modes of soils during the cold period of hydrological year and their influence on the development of processes of erosion during snowmelt, the hydrothermal mode of chernozems of different degree of erodibility of slope surfaces of Predsalairya (within Novosibirsk region) was studied. During research, it was established that the speed freezing of the soil was determined by time of establishment of constant snow cover. When forming steady snow cover at the very beginning of the cold period of hydrological year (the III decade of October) the speed freezing of arable soils made 1.5 cm/days, and later (the II decade of December) soils freeze through at 2.5 cm/days. The greatest freezing depth of Predsalairya chernozems was noted at late formation of steady snow cover which is characteristic for snowy winters. The capacity of deep-frozen layer in such winters is almost 50 cm more than in very dry winters, when the height of snow is minimum (in earlier periods of constant snow cover appearing). Depth freezing of chernozems depends not only on the sum of negative air temperatures and the quantity of solid atmospheric precipitations at the beginning of the cold period, but also on the volume of a soil profile autumn moistening. Snowmelt in little-snow hydrological years at radiation type of weather begins about 2 weeks earlier, than after snowy winters. Even at the minimum water-supply in snow (50-60 mm) the superficial drain of thawed snow is always observed. Deep and strong soil freezing and the waterproof icy screen, formed in the lower part of the humic horizon, stimulate a considerable superficial drain (Drain coefficient 0.7-0.8), whereas Drain coefficient is much smaller (0.4-0.6) at a large volume of thawed snow drain in snowy winters. Specificity of a temperature mode of Predsalairya chernozems during the cold period of hydrological year is conditioned by the fact that an icy screen impenetrable for snowmelt water is formed because of high moistening of the top soil thickness, steady snow cover and a deep and strong soil profile freezing. Therefore, despite the size of snow cover water equivalents, a considerable superficial drain (Drain coefficient > 0.5), leading to essential alienation of a solid phase of chernozems, is annually observed here. Small (about 250 m/hectare) losses of snowmelt water against the minimum snow cover in little-snow years negatively affect the replenishment of stocks of soil moisture. In such years, even after snowmelt period, one can observe essential moisture deficiency which is practically not renewable in spite of the abundance of atmospheric precipitations during the warm period of the year.

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