Yearly dynamic of the vine nutrition and its oenological consequences: focus on nitrogen and potassium

Abstract

As Jules Guyot used to say : «The Genius of the Wine lays in the Vine stock ». The wine draws it ‘s quality from the vineyard ; that is a very old idea, now widely spread. Many viticultural practices are in fact winemaking operations and the direct or indirect links between most viticultural ways and their oenological consequences are still undiscovered. Water supply along with the vine nutrition, which depend on both viticultural practices and weather conditions are major issues. The aim of the present study is to highlight the influence of these two issues on musts and wines’ composition and balance, with a focus on two key factors : nitrogen and potassium. A network of ten plots of vines has been followed between 2011 and 2014 in the Languedoc Roussillon area. Analysis of petioles from the fruit zone leaves were performed at each phenological stage, from seperate floral buds to post-maturity. The average nitrogen content in the petioles shows annual variations, with a clear difference at the beginning of the growth season. These differences can mainly be explained by the climatic variations among the different millesimes. The nitrogen levels found in the fruit zone petioles tend to converge after flowering, even though some summer accumulations can sometimes be detected, explaining some increases of the nitrogen concentration in musts. As well, right from the first phenological stages of the vine’s growth, potassium levels in petioles may vary significantly from year to year. The years knowing strong assimilations are characterized, at maturity, by a considerable decrease of potassium content in petioles, correlated to the loading of potassium in musts, leading to a sensible pH increase. This study highlights the climate impact on the nutritional dynamic of the vine, as early as the firts phenological stages and at different levels according to he grape varieties and their agro-climatic adaptation.