Mineral and Bacterial Fertilization Impact on Dehydrogenase Activity and Microbial Biomass in Acid Eutric Cambisol under Winter Wheat

Abstract

An extensive application of the high rates of mineral fertilizers inhibit the growth and activity of soil microorganisms. Biodiversity can be maintained by application of nitrogen fixing microorganisms, which could present an alternative and/or supplement to mineral nutrition. The aim of this study was to investigate the effect of non-symbiotic bacterial inoculants and different rates of mineral fertilizers on dehydrogenase activity and microbial biomass in acid eutric cambisol type of soil under winter wheat, based on the following variants: control (non-fertilized soil); 60 kg/ha N and P2O5, and 40 kg K2O/ha (N1P1K1); 120 kg/ha N, P2O5 and K2O (N2P2K2); Enterobacter sp. strains + N1P1K1; Enterobacter sp. strains + N2P2K2; Klebsiella planticola + N1P1K1; Klebsiella planticola + N2P2K2. The volume of soil microbial activity was estimated in the beginning and at the end of the plant growth. Dehydrogenase activity was estimated by spectrophotometer, while microbial biomass, in the form of CO2-C, was determined by hloroform fumigation incubation method. Studied parameters of microbial activity were significantly higher during the entire investigation period in the variant where combination of bacterial inoculants and lower rates of mineral fertilizers (N1P1K1) was applied. The intensity of soil microbial activity was slightly higher in the full maturity phase of the wheat than in its phase of intensive growth. It can be concluded that by applying bacterial inoculants we can effect on dynamics and direction of microbial processes that indirectly effect on increase and maintenance of the soil fertility and decrease the application of mineral fertilizers.