Distribution and Translocation of Nitrogen Absorbed During Early Summer by Two-Year-Old Grapevines Grown in Sand Culture

¹ Viticultural and Oenological Research Institute (VORI), Private Bag X5026, 7600 Stellenbosch, Republic of South Africa.

The grapevine shows a critical demand for nitrogen (N) during early summer (end of rapid shoot growth up to veraison). The distribution and translocation of N applied during this period were quantified for Chenin blanc grapevines grown in sand culture. Vines, in their second growing season, were labeled with ¹⁵N over a 25-day period starting at the end of rapid shoot growth (berry size: 8 mm in diameter). After labeling, the vines received standard Hoagland solution for the rest of the investigation period. Entire vines were subsequently sampled seven times over a period of 10 months: i.e., four times during the latter part of the second, and three times during the first part of the third growing season. At the first sampling date (veraison), 52% of the labeled N was found in the vegetative growth, 28% in the bunches, and 20% in the permanent structure. Between veraison and harvest, 34%, 23%, and 35% of the amounts of labeled N in the shoots, leaves, and permanent structure, respectively, were lost, presumably being translocated to the bunches. It is suggested that these figures can be regarded as realistic estimates of N turnover during the relevant period. At harvest, bunches contained 46%, vegetative growth 41%, and the permanent structure 13% of the labeled N. This distribution appears to be fixed for all N absorbed from the end of bloom up to veraison by vines with a realistic ratio for yield to vegetative growth.

Key words: nitrogen, grapevine, distribution, translocation, summer-applied N, partitioning

Submitted on August 6, 1990