Lower Petiole Potassium Concentration at Bloom in Rootstocks with Vitis berlandieri Genetic Backgrounds

The effect of rootstock on seasonal vine nutrition was monitored at three trials in Northern California: two in the Sacramento Delta with Chardonnay and Cabernet Sauvignon as the scions and one in Amador County with Zinfandel as the scion. Each site was planted with identical sets of 14 rootstocks. Leaf petioles were sampled at the three phenological stages of bloom, veraison, and harvest and analyzed for potassium (K) content. Rootstocks differed significantly in petiole K concentration at bloom, 44–53 had the highest K status at all three phenological sampling times, and Freedom also had high K status. Total K levels generally declined significantly between bloom and harvest for all varieties, although the amount and pattern of decline differed among rootstocks. Leaf lamina K concentrations were much lower than those of petioles. The ranges between the high and low values were much narrower, but trends were consistent with petiole samples. Rootstocks with Vitis berlandieri genetic backgrounds contained lower levels of petiole K at bloom, but these differences were not apparent at veraison and harvest. It is possible that water deprivation because of drip-irrigation or deficit-irrigation practices contributed to this result, as it has not been consistently observed in previous investigations.