A laboratory experiment has been performed to determine the effect of soil pollution with the herbicides: Harpun 500 SC, Faworyt 300 SL, Akord 180 OF and Mocarz 75 WG on the course of ammonification. The soil material for the experiment consisted of loamy sand of pH 6.5. The experiment comprised five replications. Soil samples in particular objects were polluted with the herbicides at rates corresponding to the dose recommended by the manufacturer: 0 – control, 1 – a dose recommended by the producer, and the rates 50-, 100-, 150- and 200-fold higher than the recommended dose. Next, nitrogen was introduced to soil in the form of L-aspartic acid, DL-alanine, L-arginine and urea in the amounts of 0 and 300 mg N kg-1 soil. Having been thoroughly mixed with the additional substances, the soil was brought to moisture equal 60% capillary water capacity and incubated for 12, 24, 36 and 48 hours at 25ºC. The study has demonstrated that the course of ammonification depended on the type and rate of a herbicide added to soil, type of an organic compound undergoing ammonification and duration of the trial. L-arginine was ammonified most rapidly, while ammonification of L-aspartic acid lasted the longest. Among the tested herbicides, the strongest inhibitory effect on ammonification process was produced by Mocarz 75 WG, which continued to exert negative influence on mineralisation of organic substances for 36 hours. The other preparations did not have such a considerable effect on the quantities of ammonified nitrogen.