Response of 'Italian Riesling' Leaf Nitrogen Status and Fruit Composition (Vitis vinifera L.) to Foliar Nitrogen Fertilization

Two-year study was conducted on Italian Riesling cultivar with the aim to compare the effect of foliar sprays with different nitrogen forms on grapevine leaf N status, yield, and nitrogen compounds in grape juice. Treatments included no fertilization (control), soil NPK treatment, and three foliar treatments [amino acids, urea, ammonia (NH4+)/nitrate] applied four times during season, also treated with soil NPK. The application of 1% w/v urea significantly increased leaf total leaf N content in the second year of study. However, there were no effects on N compounds in grape juice, since changes in free amino nitrogen (FAN), NH4+, and consequently yeast assimilable nitrogen (YAN) were not consistent among the treatments and experimental years. Although increase of vine leaf N status was achieved by 1% w/v urea, additional modifying of application time (by moving it closer to veraison) is needed, with the aim to increase N compounds in grape juice as well.