The aim of a field experiment was to determine foliar urea application in a vegetation period of potato on the content of nitrogen mineral form in the soil and potato yielding. The experiment was carried out on light soil. In autumn of the experiment cattle manure (25 t ha-1) as well as phosphorus (39 kg P ha-1) and potassium fertilizers (100 kg K ha-1) were applied on the entire area. In spring diversifield levels of fertilization with nitrogen – 0 kg N ha-1 (control object),
150 kg N ha-1 into the soil and 10%, 20%, 30% of basic N dose amounted to 150 kg N ha-1 of area were applied into the soil. The soil for examination was taken from the layer of 0-30 and 30-60 cm on four fixed dates. The study was conducted on Sante cultivar. Analyses of nitrate and ammonium ions content were carried out by reflection spectroscopy using RQ flex Merck reflectometr. During the harvest the yield of tubers and the content of nitrates in fresh matter of tubers were
determined. It was found that supplementary doses of N (15 and 30 kg N ha-1) provided as foliarapplied urea can be used to adjust N nutrition of potato crop without significant changes in yield and its nitrate content. The lowering of N-dose applied into the soil and an increase of N-dose applied into leaves caused a decrease of mineral nitrogen in the soil. The highest content of nitrate and ammonium forms of mineral nitrogen during the closing the rows phase was found stated (first date of samples testing). On the next dates of sample testing the content of N mineral significantly decreased for each object of nitrogen fertilization. The content of N-NO3 and N-NH4 was the lowest at the end of potato vegetation. The content of nitrate form was higher than ammonium form.