The aim of the research is to study the structure, humus content, microbiological activity of the dark-chestnut soil after applying bioactive substance (humic preparation Bio-Don) which contains a complex of humus substances (humic and fulvic acids) and amino-acids. To study soil structure Savvinov’s method (dry and wet sieving) was used; humus content was determined by burning in potassium dichromate; microbiological activity was studied by standard method seeding dilutions of soil suspension onto solid culture medium. It is established that bioactive substances have mediately positive effect on soil structure increasing the portion of agronomic-valuable aggregates. This happens due to enhancing the activity of rhizosphere microflora as a result of symbiotic interaction between root system and microorganisms, which population depends on the availability of root exudates secreting through rhizosphere. The analysis of microbiological activity has shown that under wheat the population of ammonifying, amino-autotrophic, oligonitrophilous, and oligotrophic bacteria in soil were in 2.3–3.2 times higher than under corn. The population of soil micromycetes was also significantly higher (by 78 %). This leads to an increase of water-resistance aggregates what is the key index of soil structure quality. The specifics of winter wheat, which forms dense fibrous root system penetrating the whole volume of the surface soil layer, facilitate to rhizosphere effect comparing to corn. As a result, the number of water-resistance aggregates under winter wheat was by 9.2 % higher than under corn. Structure coefficient under winter wheat increased from 0.3 to 0.4, and under corn decreased from 1.2 to 0.8.
Keywords: dark-chestnut soil, bioactive substances, humus, soil structure, microbial activity, rhizosphere, water resistance.
