Soil Moisture and Thermal Regimes of Complex Soil Cover.

Complex soil cover of Russian Plate landscapes has peculiarities of paleocryogenic soilscape such as areas with high organic matter content (loose zones) and compacted soil. Typically soil density varies from 0.73 g/cm³ to 1.54 g/cm³ in the arable layer and from 1.0 g/cm³ to 1.68 g/cm³ at the depth of 35-40 cm. Organic carbon content varies from 1.36% to 2.98% and from 0.23% to 4.65% in the arable layer and 35-40 cm layer, respectively. Agricultural practice altered soil physical properties and resulted in formation of compacted subsoil layers, spatially distributed differently from soil subtypes. Spatial patterns of the compact and loose zones create a specific structure in water and temperature distribution. Objective of the study was to identify the spatial distribution in soil water and thermal regimes and to relate regimes to zones with different soil density. Soil water and thermal regime monitoring was conducted during 5 years at different temporal and spatial scales (from 0.01 to 4 ha). Temperature measurements showed that the loose soil layers were slowly warmed up during spring and summer months and became cold in winter due to low thermal diffusivity. The loose horizon accumulates and conserves more water during wet periods and becomes dryer during drought periods, compared to the compacted horizons. The results of the monitoring illustrate spatial variability of the hydrothermal fields in the studied area and its relationship with locations of the compacted and loose soil zones. For the quantitative assessment of the regimes pedotransfer functions were developed to calculate soil water retention, hydraulic conductivity, thermal diffusivity from soil bulk density and soil organic carbon content. Good agreement was obtained between measured and estimated with the pedotransfer functions water content and temperature distributions in the soil.