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Foliar fertilization with nitrogen compounds has been reported to have a substantial impact on grape composition. Overall, this practice has been associated with an increase of grape nitrogen compounds. However, much less is known about its real impact on phenolic composition, especially through more than one year. In the current work, grape phenolic composition was studied after carrying out foliar treatments with two nitrogen sources (phenylalanine and urea) at 0.9 kg N/ha over two consecutive vintages. Phenylalanine treatments increased the concentration of a few anthocyanin compounds in comparison with control, although hydroxycinnamic acids were decreased in the first year of the study. In contrast, urea application increased some flavanol compounds in the second year, while no effect was observed in the first one. Overall, it was not observed a significant decrease of phenolic compounds which, in contrast, has been traditionally associated with high nitrogen supply by soil fertilization. In conclusion, the foliar application of phenylalanine and urea at 0.9 kg N/ha did not exert a big impact on grape phenolic composition., Many thanks for the financial support given by the Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA)-Gobierno de La Rioja under the project RTA2013-00053-C03-01 and Gobierno de La Rioja under the project R-11-1. J. P. and T. G.-C. also wish to thank the INIA-Gobierno de La Rioja and European Social Fund for their contracts. T. G.-C. also thanks MINECO for funding her Ramón y Cajal contract.

There is little available information about the effects of seaweed biostimulation to grapevines on grape juice and wine nitrogen content. This trial aimed to study the effects of the biostimulation through an Ascophyllum nodosum fertilizer to Tempranillo grapevines at low (Ld: 0.25 % v v−1) and high (Hd: 0.50 % v v−1) dosages on must and wine amino acids and ammonium during two seasons. The content of these compounds in musts and wines were measured by UHPLC. The results showed that precipitations could have affected berry size and enological parameters of musts and wines. In the driest season (2017), Ld treatment increased the concentration of several amino acids in musts such as His, Arg, Ala, Gaba, Pro, Val, Met, Ile, Trp, Orn, Lys, and total amino acids. In the rainiest season (2018), the Hd treatment was the most effective, increasing the content of His, Cit + Thr, and Trp. Generally, a high yeast assimilable nitrogen (> 279.4 mg N L-1) content in the must allowed to reach a high concentration of amino acids in wines. Therefore, seaweed foliar application to grapevines allowed to improve amino acid content in musts in both seasons and its effectiveness depended of climate conditions of the season and the dosage applied., G. G.-G. thanks for the financial support given by CONICYT PFCHA/Doctorado Becas Chile/2016 – 72170532. T. G.-C., P. R.-B., and E.P. P.-Á. are funded by the Spanish Ministry of Science, Innovation and Universities.