Amino Acid Composition of White Grape Juices as Affected by Soil Urea Fertilization

The aim of this work was to test the effects of soil urea fertilization on yield, grape juice soluble solids, total acidity, and amino acid composition of Chardonnay, Welschriesling, and Riesling grape varieties. The experiment was conducted in a vineyard with repeated records of low yeast-assimilable-nitrogen content in must and the corresponding grape juices in years prior to the experiment. Urea was applied after completion of flowering. Treatments included the control without fertilization, 5.5, 16.8 and 28.1 g N vine-1. Urea fertilization generally increased yield components and amino acid concentrations. Fertilization with 28.1 g N vine-1 prolonged grape ripening, regarding soluble solids and total acidity values. Fertilization with 28.1 g N vine-1 was not so effective in improving amino acid concentration compared to other fertilization treatments. This leads to conclusion that fertilization with 28.1 g N vine-1 seems excessive and unnecessary regarding delayed fruit ripening and inconsistent effect on amino acid composition.