Effect of mineral and organic additions on soil microbial composition

. The aim of the study was to evaluate the effect of different mineral-organic mixtures on changes in soil microbial composition and chemical properties. The design of the pot exper iment included 6 treatments: soil without fertilization – C, soil fertilized with mineral NPK fertilizers – MF, soil with NPK + 3 or 6% lignite and 3% zeolite-vermiculite composite (MF+CW3%, MF+CW6%), soil with NPK + 3 or 6% leonardite and 3% zeolite-vermiculite composite (MF+CL3%, MF+CL6%). The test plants were spring oilseed rape and spring wheat. The highest number of microorganisms was observed: for oilseed rape – in the soil of the MF+CW3% and MF+CW6% treatments, and for wheat – in the soil of the MF+CL3% and MF+CL6% treatments. The maximum percentage increase in the number of analysed micro organisms, for spring rape and spring wheat, respectively, was: bacteria 190% (MF+CW3%) and 1198% (MF+CL3%), mould fungi 221% (MF+CW3%) and 1601% (MF+CL3%), Azotobacter spp. 248% (MF+CW6%) and 251% (MF+CL3%), actinomycet es 116% (MF+CW3%) and 251% (MF+CL3%). The beneficial effect of the applied mineral-organic mixtures on soil biological activity is closely related to the effect of these materials on soil chemical properties, such as pH or electrical conductivity, which was confirmed by the calculated correlation coefficients.