<p style="text-align: justify;">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.</p><p style="text-align: justify;">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.</p><p style="text-align: justify;">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.</p>
<p style="text-align: justify;">Grapevine nitrogen status was assessed by nitrogen content in leaf blade and petiole at veraison, in must at harvest and in pruned wood in December. The comparison of these indicators were done in vineyards bearing adults plants in the Atlantic and Mediterranean climates. Soil nitrogen offer were changed by soil grass cover, fertilization and irrigation. Leaf blade nitrogen (LBN) content cannot be simply predicted from soil texture, training characteristics and climate. Petiole and wood nitrogen content was less precise indicators compared to LBN content per unit dry weight. LBN content based on unit of leaf area usually constant along the growing season provides a complementary information on the leaf photosynthetic capacity and nitrogen availability for grapevine in summer. LBN content informs on the early growth grapevine access to soil and reserve nitrogen.</p><p style="text-align: justify;">Must and leaf blade nitrogen contents are significantly correlated. But it is shown that must N content is also changed by the yield and the soil capacity to provide nitrogen to the grapevine in summer. A simple predicting model of N in must is proposed. It is based on the availability of N in spring and summer and the positive effect of spring N on berry set up. Leaf blade and must N content considered both provided a complementary information on the grapevine N nutrition along the season.</p><p style="text-align: justify;">Sampling conditions for LBN content was tested. Primary leaves of a rank above 6 are very similar in N content and most representative of the grapevine N status. The LBN content on a leaf area basis is a more versatile expression because less variable along the growing season. The expressions of LBN content on the dry weight and leaf area can be obtained from a simple analysis by sampling leaf disks.</p>
Une expérience multifactorielle a été entreprise dans le dessein d'évaluer l'effet de la fumure azotée à deux niveaux, de quatre porte‐greffe et de deux systèmes de taille sur la sensibilityé du cépage Merlot àBotrytis cinerea. II est apparu qu'une fumure excessive en azote (100 kg N/ha/année) augmente d'une façon significative la sensibilityéà la pourriture grise. Le porte‐greffe S04 a également favorisé le développement du champignon, mais sous l'effet d'autres mécanismes. Quant à la taille, elle n'a pas révélé d'action particulière dans le cadre de cet essai limité. On peut done admettre que B. cinerea peut être contenu dans une certaine mesure par une fertilisation azotée bien dosée et par le choix approprié du porte‐greffe.
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