Nitrogen foliar uptake and partitioning in "Cabernet Sauvignon" grapevines

Avoiding nitrogen (N) deficiency in grapes (Vitis vinifera L.) is necessary to satisfy its annual nutrient requirements. Foliar nutrition is a rapid method to decrease temporary N deficiency while reducing uptake during the vegetative and reproductive season. To better understand N uptake dynamics by foliar spray applications and its partitioning in vine organs, labeled N (15N) was used in the present study. The trial was undertaken at the IASMA vineyard on fifteen - year old vines of the cultivar ‘Cabernet Sauvignon’ raised on a cordon spur training system. Foliar N nutrition was applied during four main phenological phases (pre-flowering, pre-bunch closure, veraison and harvest) on four vines per time using an ammonium sulfate solution where 15N was enriched to 10 atom %. Each vine was fertilized with 10 ml of solution applied on both sides of the leaf which therefore received a total of 21.2 mg of 15N. After one week the vines were destructively harvested and then divided into: axis of shoot, leaves, bunches and/or inflorescences, wood, bark, fine (<2 mm) and coarse (>2 mm) roots. Each sample was dried and weighed, and a sub-sample was used to determine N uptake. There was a large difference in N uptake efficiency between the phenological phases. Pre-flowering uptake efficiency was 38.0%, in pre-bunch closure 30.0%, at veraison 21.7% and at harvest 66.0%. This difference can be explained by quantifying the timing and quantity of rain fall after treatment.