The laboratory experiment was set up on a podzolic soil in two variants. In one of them non-sterile sewage sludge was introduced into the soil, and in the second - the same sludge but subjected previously to the process of sterilisation. In both variants the same doses of the sludge were applied: 30 (1%), 75 (2.5%), 150 (5%), 300 (10%) and 600 Mg·ha-1 (20%). Then, after 0.5, 1, 2, 3, 4 and 5 months, the soil of both experimental variants was analysed for the numbers of bacteria and fungi decomposing proteins, the rate of the process of ammonification, the rate of the process of nitrification, and for proteolytic activity. The results obtained revealed a stimulating effect of the sludge, both sterile and non-sterile, on the numbers of the microbial groups under study and on the rate of nitrification and protease activity. Only the process of ammonification was subject to inhibition. The observed effects of the sludge were the most pronounced in the case of the higher sludge doses. Significantly greater numbers of protein-decomposing fungi and higher activity of almost all (except for ammonifcation) analysed biochemical parameters in the soil with non-sterile sludge compared to that with sterile sludge indicate an effect of microorganisms from the sludge on the microbiological transformations of nitrogen in soil amended with sewage sludge.
The effects of a microbial inoculant (Thervelics®: a mixture of cells of Bacillus subtilis C-3102 and carrier materials) on rice (Oryza sativa cv. Milkyprincess) and barley (Hordeum vulgare cv. Sachiho Golden) were evaluated in four pot experiments. In the first and second experiments, the dry matter production of rice and barley increased significantly by 10–20% with the inoculation of the mixture at a rate of 107 cfu ⋅ g–1 soil compared with the non-inoculated control. In the third experiment, the growth promoting effects of the mixture, the autoclaved mixture and the carrier materials were compared. The dry mater production of rice grains was the highest in the mixture, and it was significantly higher in the three treatments than in the control, suggesting that the carrier materials may also have a plant growth promoting effect and the living cells might have an additional stimulatory effect. To confirm the efficacy of the living cells in the mixture, only B. subtilis C-3102 cells were used in the fourth experiment. In addition, to estimate the mechanisms in growth promotion by B. subtilis C-3102, three B. subtilis strains with similar or different properties in the production of indole-3-acetic acid (IAA), protease and siderophore and phosphatesolubilizing ability were used as reference strains. Only B. subtilis C-3102 significantly increased the dry matter production of rice grains and the soil protease activity was consistently higher in the soil inoculated with B. subtilis C-3102 throughout the growing period. These results indicate that the microbial inoculant including live B. subtilis C-3102 may have growth promoting effects on rice and barley.