The Influence of Selected Soil Parameters Modified With Sewage Sludge and Fly Ash Fertilization on the Total Number of Bacteria (TNB) and Bradyrhizobium Species at Soybean Agroecosystem

In this study, the influence of the environment on soil conditions, e.g. heavy metals and soil magnetic susceptibility, on the total number of bacteria and the species of Bradyrhizobium in the field cultivation of the soybean variety Lissabon, the seeds of which had been inoculated with HiStick®Soy, were evaluated. Field experiments were carried out with the random plot method on the Cambisol with a texture of silt loam. The experiment consisted of 24 objects in six combinations and four replications using sewage sludge and fly ash. In the soil samples, the total number of bacteria and the number of the species of Bradyrhizobium were determined using the culture-plate method. The total content of heavy metals (Cu, Zn, Cd, Ni, Pb, Cr, Hg, Fe) in the analyzed objects, compared to the limit values, allowed them to be classified as uncontaminated soils despite the application of sewage sludge and fly ash according to the experimental scheme, showed a significant difference between them. The study of the magnetic parameter χ indicated a significant differentiation between objects from 34.0 to 65.8 × 10-8m3kg-1. High correlation coefficients between χ and Fe (r = 0.789), Zn (r = 0.653), Cr (r = 0.617) and TOC (r = 0.949) indicated that the source of these elements was external organic matter. Biological tests (total content of bacteria and species of Bradyrhizobium) in different experimental variants indicated significant relationships between them and showed the resistance of the microbial community in the field cultivation of Lissabon soybean to heavy metal contamination from sewage sludge and fly ash.