Influence of Scion and Rootstock on Seasonal Foliar Levels of N and K

Over the past three years, petiole and blade tissues were collected at two sites with 14 rootstocks, at each of three phenological stages: bloom, veraison and harvest. All samples were analyzed for two forms of N (NO3-N and total N) and for K. At an additional site in Sonoma samples were collected from a trial with nine rootstocks and two potassium (K) applications treatments (+K or -K). The Sonoma site samples were also analyzed for calcium and magnesium. In addition, samples were collected from a scion variety trial. Rootstocks have a significant effect on foliar levels of N and K. Both N and K vary significantly over the seasons with the highest generally being bloom and lowest levels of each being the harvest sample. Blades and petioles do not give identical nutrient levels or seasonal trends among rootstocks or trial. These data will be referenced with the Rootstock Field Evaluation project in order to assess whether and to what extent nutrient data correlate with growth and yield components and with juice chemistry.