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Soil microorganisms play a key role in many biochemical processes essential for the environment and for the ecological and production functions of soils, hence they are very important quality indicators. The study aimed at evaluating the effect of 1 and 2% additions of wheat and miscanthus straw biochars on soil enzymatic activity (dehydrogenases, urease, phosphatases) and the number of microorganisms (bacteria, fungi, actinobacteria). Pot experiments were carried out on soil with a loamy sand texture. The geometric mean of enzyme activities, biological index of fertility, and the integrated total enzyme activity index were used to explore the relationships between soil enzyme activities and the microbiological and chemical properties of soil. The addition of 1% miscanthus straw biochar had the most beneficial effect on the number of bacteria and fungi (increase by 380 and 26%, respectively), and 1% wheat straw biochar on the number of actinomycetes (increase by 273%). The correlation analysis between the number of actinomycetes and the chemical parameters of the soil showed the significant effect of the content of Ntotal (r = 0.76) and Ctotal (r = 0.85). The values of biological index of fertility, total enzyme activity index and geometric mean of enzyme activities indexes showed that the best quality of soil was produced by a 2% addition of wheat straw biochar. [ABSTRACT FROM AUTHOR]

The variety of technological conditions and raw materials from which biochar is produced is the reason why its soil application may have different effects on soil properties and plant growth. The aim of this study was to evaluate the effect of the addition of wheat straw and Miscanthus giganteus straw (5 t DM ha-1) and biochar obtained from this materials in doses of 2.25 and 5 t DM ha-1 on soil enzymatic activity, soil ecotoxicity, and plant yield (perennial grass mixture with red clover). The research was carried out under field conditions on soil with the granulometric composition of loamy sand. No significant effect of biochar amendment on soil enzymatic activity was observed. The biochar-amended soil was toxic to Vibrio fischeri and exhibited low toxicity to Heterocypris incongruens. Application of wheat straw biochar and M. giganteus straw biochar in a dose of 5 DM ha-1 contributed to an increase in plant biomass production by 2 and 14%, respectively, compared to the soil with mineral fertilisation. Biochars had a more adverse effect on soil enzymatic activity and soil ecotoxicity to H. incongruens and V. fischeri than non-converted wheat straw and M. giganteus straw, but significantly increased the grass crop yield. [ABSTRACT FROM AUTHOR]