Changes in the microbial population in leached chernozem during soybean cultivation inoculated by various symbionts

Abstract

One promising approach to increasing soybean yields is the use of symbiotrophic microbial biopreparations for seed inoculation. This enhances plant adaptability, improves soil health, and reduces the negative impacts of conventional chemical farming. The primary research goal was to investigate the abundance and dynamics of microbial populations in leached chernozem soils inoculated with the symbiotrophic bacteria Bradyrhizobium japonicum (Rhizotorfin), the associative bacteria Artrobacter mysorens (Mizorin), and Glomus fungi of strain 8 (Mycorrhiza), both individually and in combination. The studies were conducted in the fields of the peasant farm enterprise KFKh Ivanova A.N. in the forest-steppe zone of the Biya-Chumysh Upland of the Altai Region from 2021 through 2023. The microbiological composition was studied using standard inoculations of soil suspensions on solid nutrient media. During the flowering stage on a year with favorable moisture conditions, saprophytic microorganism counts reached 16.06-33.49 million CFU, while amylolytic counts reached 19.05-39.0 million CFU; these numbers decreased by autumn. A 1.4-2.1-fold increase was observed in the numbers of bacteria growing on meat-peptone agar and consuming organic forms of nitrogen, while amylolytic bacteria and actinomycetes utilizing mineral nitrogen increased 1.6-2.2 times. Mycorrhiza inoculation had the least significant effect, while rhizotorphin with myzorin and mycorrhiza had the greatest effect. Inoculation reduced fungal counts 1.1-1.4 times during the summer with this effect mitigating by harvest time. The weather conditions had the greatest influence on the development of microorganisms (17.71-78.54%), while biofertilizers had a 12.16-21.21% influence. The counts of saprotrophic and amylolytic microorganisms, both during the flowering stage and during the harvesting period, had a significant impact on soybean yields (r = 0.60-0.86), while fungi inhibited it (r = 0.01-0.27).