The aim of the study was to assess the absorbtion degree of different nitrogen forms (ammonium, nitric, amidic) from soil into the plant by using nuclear techniques and 15N isotope as a tracer. In the same time, the effect of foliar fertilization on increasing the efficiency of nitrogen use by biostimulating the plant up-take was highlighted. Urea and ammonium nitrate labeled with 15N isotope (10% from total nitrogen content of the fertilizers being covered by 15N isotope) were incorporated in soil. In order to highlight the efficiency of foliar fertilization, fertilizers having NPK matrix with mezo and microelements and proteic organic compounds (animal and vegetal) were designed and obtained. The effects of experimental treatments on isotopic indicators (15N/14N isotopic rate, δ 15N isotopic accumulation degree, 15N isotope export, absorbtion degree of 15N isotope) from plant were assessed. The tested plant was maize (Cortes hybrid). The values obtained were statistically analyzed by using variance analyze, with two factors, Duncan test of multiple comparison, multiple comparison threshold α= 0.05. The results of agrochemical testing showed that the absorbtion degree of 15N isotope from soil into maize plant was highest for the amidic (N-NH2) form of the nitrogen comparing with the other forms (N-NO3, N-NH4).