Changes in the Chemical and Biological Properties of Arable Soils with Different Duration of the Freezing Period

The results of a 2-year vegetation experiment to study the effect of the duration of the frost-free period on the chemical properties and biological activity of agrokashtan soils and agrochernozem are presented. The task of the experiment was to assess changes in soil properties that may occur with further warming of the climate and a reduction in the time of stay of soils in the frozen state. The first variant of the experiment provided for incubation of soils in a frozen state in winter for 160 days, the second – 56 days, in the third variant, the soil was incubated throughout the winter period at a temperature of  >0°C. Before winter incubation, the soil was moistened to 60% of FMC, mineral fertilizers and straw were applied. In the spring, spring wheat of the Zlata variety of the selection of the Moscow NIISH “Nemchinovka” was sown in the soil. Throughout the growing season, soil samples were kept in the vegetation pavilion in conditions of natural moisture and illumination. Sampling and measurements of biological properties were carried out in the spring period 10 days after the samples were transferred from the refrigerator to the vegetation pavilion. It was found that, depending on the duration of the freezing period of the studied soils, the most sensitive indicators for temperature changes were microbial biomass (C-LED), basal respiration rate (V-BASRR) of the microbial community and the number of microorganisms (NMO) growing on soil agar and on a rich medium. The soils that were incubated without freezing had the lowest values of C-LED and V-BASRR. The increase in the freezing period of the soil affected the acidity of the soils. In the variants with prolonged freezing in the 2^nd year of the study, the pH value increased. For agrochernozem, a decrease in the content of P₂O₅ was noted as the freezing period increased. For agrokashtan soils, this pattern was less pronounced. In these soils, a tendency to decrease the C : N ratio was revealed with an increase in the time spent in the frozen state. The content of C_org, as well as macro- and microelements in all variants practically did not change during the 2 years of the experiment.