Distribution and Translocation of Nitrogen Absorbed During Late Spring 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.

Distribution and translocation of spring-applied nitrogen (N) were quantified for two-year-old Chenin blanc grapevines grown in sand culture. Vines were labeled with ¹⁵N over a four-week period stretching from the end of bloom to the end of rapid shoot growth. From this stage onwards, vines were fed unlabeled KNO₃, and entire vines were sampled eight times over a period of 11 months. Five samples were taken in the second and three during the third growing season. At the first sampling date (one week after the end of labeling), 55% of the labeled N was found in the vegetative growth, 20% in the bunches, and 25% in the permanent structure. Up to harvest, the total N content of shoots and leaves did not decrease, but the amount of labeled N showed losses of 48% and 21%, respectively. This indicated the importance of these organs as transitional reservoirs for N absorbed during late spring. Spring-applied N was also translocated from the permanent structure, resulting in the bunches containing 45% of the labeled N at harvest. Nearly 40% of the spring-applied N still present in the leaves at harvest was translocated to the shoots and the permanent structure during leaf senescence. At the end of dormancy, the fine roots, rootstock-and scion trunks contained similar concentrations of labeled N, but the rootstock trunk showed a larger proportion of soluble N. At the start of the third growing season, new growth utilized reserve N more readily from the permanent wood than from the roots, but roots played an important role at a later stage, i.e., during bloom. The annual turnover of N for the whole vine appeared to be in the order of 80%, which is considerably higher than that of some other deciduous crops.

Key words: nitrogen, grapevine, distribution, translocation, spring-applied N

Submitted on September 8, 1989

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