Changes in the Chemical and Biological Properties of Arable Soils Following Freezing Episodes of Different Duration

The effect of a duration of a freezing episode on the chemical properties and biological activity of agro-chestnut and agro-chernozem soils was studied in a 2-year vegetation experiment. The purpose of the experiment was evaluation of changes in soil properties that may occur in the case of further climate warming and reduction of the soil freezing period. The first and second experimental variants included soil freezing in the winter period for 160 and 56 days, respectively; in the third variant, soil was incubated at positive temperatures for the whole winter period. Prior to winter incubation, the soil was moistened to 60% of moisture-holding capacity (MHC) and supplemented with straw and mineral fertilizers. In spring, a spring wheat (var. Zlata) bred by the Nemchinovka Federal Research Center was sown in the studied soil samples. During the whole vegetation season, soil samples were kept in a vegetation pavilion under conditions of natural moisture and illumination. The sampling and the measurement of biological properties of soil samples were carried out in spring, 10 days after the samples were transferred from a refrigerator to a vegetation pavilion. Depending on the duration of the freezing episode, the most sensitive indicators of temperature changes were the microbial biomass (V-SIR), basal respiration rate of a microbial community (V-BASRR), and the number of microorganisms (CFU) growing on soil agar and nutrient-rich medium. Soils incubated without freezing were characterized by the lowest V-SIR and V-BASRR values. The longer freezing episode affected the soil acidity. In the case of long-term freezing, the pH value increased in the second year of study. As the duration of a freezing episode increased, the Р 2 О 5 content in agro-chernozem soil decreased. In the case of agro-chestnut soil, such a decrease was less manifested, but the tendency to the reduction of the C : N ratio was observed. In all variants, the content of organic carbon, as well as macro- and microelements, remained almost unchanged during the whole 2-year experiment.