Based on the survey data was calculated nitrogen balance method “on the surface of the field” on farms within the catchment area of the Rokietnica river in Podlaskie. Based on the analysis of the results obtained, it was found that almost half of all farms participating in the survey, exceeds the safe limit of the positive difference in the balance sheet in accordance with the Code of Good Agricultural Practice. It was also a positive correlation between the measured values of the concentrations of nitrate (V) and the amount of waste manure and mineral fertilizers on farms, reflecting the migration of unused nitrogen in the soil profile and the component of pollution of surface waters.