Establishing Critical Values of N and K for Grapevines

Petioles were collected in three different vineyards at bloom, veraison and just prior to harvest. The Thompson Seedless vineyard was located at the Kearney Ag Center; the Chardonnay vineyard was located in the Carneros district of Napa Valley and the Cabernet Sauvignon vineyard near Oakville in the Napa Valley. Prior to bloom the following treatments were imposed: 1.) Vines that were not irrigated prior to bloom, 2.) Vines that were irrigated several times prior to bloom and 3.) Vines that were fertilized and then irrigated. Two fertilizer amounts were used in the Thompson Seedless (50 and 100 lbs. N per acre) and Cabernet (40 and 80 lbs. N per acre) vineyards while only one fertilizer amount was used in the Chardonnay vineyard (80 lbs. N per acre). The Non-irrigated treatment in the Thompson Seedless and Cabernet vineyards at veraison and pre-harvest consisted of vines in which irrigations were terminated two weeks prior to sampling. The Non-irrigated treatment in the Chardonnay vineyard was not irrigated all season long. Each treatment was replicated four times at the three locations.

At the bloom and veraison sample dates, petioles were collected at various times during the day; 0800, 1200 and 1600 hours. At veraison and prior to harvest petioles were also sampled before sunrise. On all three dates, petioles were taken from leaves exposed to direct sunlight and leaves that were in the shade at the time of sample. At bloom, petioles were also sampled from leaves opposite the cluster.

At the time this report was written not all of the petiole samples had been ground for nutrient analysis. In addition, none of the leaf, stem or clusters sampled from each treatment on each sample date had been ground. However, it was possible to analyze all petiole samples from one block at bloom, veraison and pre-harvest in the Thompson Seedless vineyard and all samples in one block at bloom and veraison in the Chardonnay and Cabernet vineyards.

Based upon the limited data reported on herein, several conclusions could be reached. As expected, N fertilizer application had a significant effect on petiole nitrate-N and total N at all three locations on all three, sample dates. The potassium nitrate fertilizer also significantly increased petiole K. Sampling leaves exposed to direct sunlight versus those taken from the shade had a significant effect on petiole nitrate-N and K. At bloom, petiole nitrate-N was generally greater in the sunlit leaves compared to the shaded leaves. The petioles of sunlit leaves collected at veraison and pre-harvest, however, had lower nitrate-N and K values than the shaded leaves in all three vineyards. In addition, petioles collected from leaves opposite a cluster had lower values of nitrate-N and K at the three locations. Irrigation amount (no applied water vs. applied water) also affected petiole nutrient status. In general, non-irrigated vines had greater values of nitrate-N than the irrigated vines. The results indicate that leaf type and irrigation amount will affect petiole nutrient values. Whether time of day significantly affects petiole nutrient status awaits the analysis of additional replications at each location.

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