Original research articles

Measurement of total nitrogen and assimilable nitrogen in grape juice to assess vine nitrogen status

Abstract

Five indicators of vine nitrogen status were compared for their accuracy to differentiate two levels of nitrogen fertilization (0 and 45 kg N / ha) : petiole total nitrogen content, leaf blade color intensity measured by a device called “N-tester”, grape juice total nitrogen content, grape juice assimilable nitrogen content and grape juice ammonium content. Differences in must total nitrogen content and must assimilable nitrogen content were highly significant between fertilization levels. They can be considered as two powerful tools to assess vine nitrogen status. Levels of must total nitrogen content and must assimilable nitrogen content were highly correlated.

Mineralizing must in order to measure its total nitrogen content is difficult, mainly because of the presence of large amounts of sugar. This operation can take more than 12 hours and it can fail because of caramelization and the appearance of foam. We propose mineralizing must by means of microwave. Complete mineralization was obtained in only one hour. No foam or caramelization was observed on any of the samples mineralized.

Vine nitrogen uptake is likely to vary to a considerable extend with soil parameters, even if no nitrogen fertilization is applied. Figuring among those parameters are: soil organic matter content, organic matter C/N ratio and soil organic matter turnover. The latter depends mainly on soil temperature, soil aeration, soil pH and soil moisture content. Differences in vine nitrogen status depending on the soil type were clearly evidenced by measuring must total nitrogen and must assimilable nitrogen at ripeness. Limited nitrogen uptake, as a result of particular soil conditions, can limit vine vigor and be a quality enhancing factor in red grape production. This emphasizes the role of moderate environmental stress in the production of high quality potential grapes.

Authors


Cornelis van Leeuwen

k-van-leeuwen@enitab.fr

Affiliation : Bordeaux Sciences Agro, Institut des Sciences de la Vigne et du Vin (ISVV), Ecophysiology and Functional Genomics of the Vine (EGFV), UMR 1287, 33140 Villenave d’Ornon, France


Philippe Friant

Affiliation : ENITA de Bordeaux, 1 Cours du Général de Gaulle, 33175 Gradignan cedex (France)


Jean-Pierre Soyer

Affiliation : I.S.V.V., UMR Écophysiologie et Génomique Fonctionnelle de la Vigne, INRA, University of Bordeaux 2, University of Bordeaux 1, ENITA, Villenave d'Ornon, France; INRA, Domaine de la Grande Ferrade, BP 81, 33883 Villenave d'Ornon, France


Ch. Molot

Affiliation : Ecophysiologie et Agronomie Viticole, UMR OEnologie Ampélologie, INRA Centre de Bordeaux, BP81 33883 Villenave d’Ornon, France


Xavier Choné

Affiliation : Consultant viticulture, 5 rue Eugène Delacroix, 33150 Cenon Bordeaux, France


Denis Dubourdieu

Affiliation : Faculté d’oenologie, UMR 1219 OEnologie, Université de Bordeaux, ISVV, 210, chemin de Leysotte, CS 50008, 33882 Villenave d'Ornon, France

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