The impact of mineral and organic supplements on the abundance of selected groups of culturable microorganisms in soil contaminated with heavy metals

The impact of lignite and leonardite combined with a NaX-C composite on the abundance of selected groups of culturable microorganisms in soil contaminated with Pb, Cd and Zn was tested. For this purpose, a 7-month incubation experiment and two-year pot experiments were conducted. The pattern of both experiments was analogous and included: soil without fertilization (C); soil fertilized with NPK mineral fertilizers (MF); soil with NPK + 3 or 6% lignite (MF+CW3%, MF+CW6%) and 3% zeolite-carbon composite (NaX-C); soil with NPK + 3 or 6% leonardite (MF+CL3%, MF+CL6%) and 3% zeolite-carbon composite (NaX-C). The test plant in the pot experiment was the Kosynier variety of maize. The soil material was used to estimate the abundance of general bacteria, mold fungi, actinomycetes (actinomycetales), ammonification bacteria and bacteria from the Azotobacter genus. The study found that the application of lignite and leonardite combined with a NaXC composite had generally contributed to a significant increase in the total nitrogen content and a decrease in the total carbon content in soil in the pot experiment. In general, the mineral-organic mixtures had a stimulating effect on the analyzed groups of soil microorganisms in both experiments, but the dominant groups in the pot experiment were total bacteria and ammonifying bacteria, while in the incubation experiment, fungi and actinomycetes were the prevalent groups. An RDA analysis indicated that mold fungi, bacteria, actinomycetes and amminofers were positively correlated with the EC, total nitrogen and carbon.