The effect of carcinogenic N-nitrosoamines (NA), NA-producing tetramethylthiuram disulfide (TMTD) pesticide, and of various doses of nitrogen fertilizers (90, 180, and 270 kg/ha) on the forming and vital functions of microbiocenosis of light gray forest soil was studied. The quantity, nitrifying activity, and gas production of nitrifying bacteria increased under the influence of NA. The nitrosodimethylamine (NDMA) and the nitrosodibutilamine (NDBA) changed the correlation between the number of soil-inhabiting fungi and bacteria so that the former prevailed. The greatest effect was observed on the twentieth day of cultivation of the soil when high concentrations of NDMA (50 mcg/kg) and NDBA (105 mcg/kg) were used. The typical dominant species among the fungi was the phytotoxigenic Penicillium funiculosum. The nitrosationable pesticide tetramethylthiuram disulfide (TMTD) applied with nitrogen fertilizers in a dose of 180 and 270 kg/ha exerted an influence on the microbiocenosis of the soil similar to NA. The potato yield decreased and the ecology of microbiocenosis deteriorated under these conditions in a model vegetable experiment. It is suggested that the nitrosoamines and their precursors may change the balance of nitrogen, decrease the yield of plants, and deteriorate the ecological balance.