Leaf and must nitrogen content two complementary indicators of grapevine nitrogen status
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.
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.
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.
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