Aims: The aim of this work is to test the effects of soil-applied nitrogen (N) at budbreak and subsequent foliar-applied N at veraison on the N composition and partitioning in berries of water stressed Vitis vinifera L. cv. Sauvignon blanc vines.
Methods and results: N fertilizer was applied to the soil at budbreak at doses of 30 or 60 kg N/ha, while the control did not receive any treatment. This did not increase N content of leaves and the vines showed symptoms of N deficiency from the beginning of the season. In order to overcome this deficiency, N foliar sprayings were applied at veraison at doses of 2.5 or 5 kg N/ha to vines having received 30 or 60 kg N/ha of soil-applied N, respectively. Total N of berry flesh responded to N foliar fertilization more than that any other berry part, whereas amino acids in skins were the more affected by N foliar fertilization than those of other berry parts. Only the 60 soil/5 foliar N treatment produced a measurable increase in the total, assimilable and amino N in berry juices at maturity. Assimilable N was a better indicator for N summer uptake by the vine than total N. Of all amino acids, arginine showed the highest increases following N fertilization and could be considered among the better indicators to distinguish between N summer fertilization treatments.
Conclusion: In conditions of severe water deficit and N deficiency, fertilization at a dose of 60 kg/ha soil-applied N combined with 5 kg/ha foliar-applied N improved fruit fermentability. Results support the use of foliar fertilization at veraison as a tool for enhancing grape quality and to a certain extent the style of wine.
Significance and impact of study: This work helps to provide insight into the effect of N soil fertilization along with foliar fertilization on waterstressed vines. This may be useful in fertilization programs in the Mediterranean area and may help to choose the type and the rate of the N fertilization in case of severe vine water deficit. Also, we provide information of utmost importance on the distribution of summer foliarapplied N in grape tissues.
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