The paper presents the results of research on the correlation between the dose and types of mineral fertilizers and content of nitro compounds accumulated of corn and alfalfa in different phenological phases. As fertilizers were using: urea and amofos at the normal doses and overdoses, and as research material were used of forage crops: the maize and the alfalfa. As a result of the research it was found that forage crops the content of nitrites in both the experimental variants as well control variant did not exceed the permisible limit. The content of nitrates in the maize and the alfalfa collected from experimental lots exceeded that of crops grown with natural fund (control lot), respectively from 2,45 to 18,70 times and 4,06 to 10,34 times.  The greater content of nitrates was detected in maize grown with mineral fertilizer  in the cobs in the wax phase (805,00 mg/kg - 1032,00 mg/kg) and in alfalfa in the beginning of the burgeoning and full burgeoning phase (1033,97 mg/kg - 978,10 mg/kg). So, as a result of research it was found that the accumulation of nitro compounds in the agricultural crops directly has depended on the type and doses of mineral fertilizers administered in the soil and phenological phases.