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Unformatted text preview: VEN 2 Mineral Nutrition of grapevines and Fertilization Guidelines Larry E. Williams Background Commonly observed grapevine deficiencies in California include those associated with nitrogen, potassium, zinc and boron (Christensen et al., 1982). Less common deficiencies include those of iron, magnesium and manganese. Lastly, toxic effects of nitrogen, chloride and boron have been observed in California vineyards. One of the most important questions to answer in a vineyard fertilization management program is: How does one determine the need to fertilize? Many locations in the San Joaquin Valley and elsewhere in California have ground water pollution problems. The pollutants include, among others, nitrates. Therefore, a fertilization program should try to minimize the leaching of mineral nutrients below the root zone. Once the decision to fertilize has been made then one must determine how much and when to apply the fertilizer. Fertilizers can be costly and one can become more cost efficient if educated decisions regarding vineyard fertilizations are made. Assessing vineyard/vine mineral nutrient status There are various means to determine the need to fertilize grapevines. The observation of foliar and/or fruit mineral nutrient deficiencies on vines can be used. Unfortunately, these symptoms could indicate that the deficiency may already have caused a reduction in yield. Some grape producing countries use soil analysis to establish the need to fertilize a vineyard. However, it has been concluded that soil analysis for the determination of N, K (potassium), Mg (magnesium) and Zn (zinc) fertilization requirements in California is of no value (Christensen and Peacock, 2000). Those authors do conclude that soil and water analysis can be used to determine B (boron) toxicity levels. Vine tissue analysis has long been used in California to assess the nutrient status of grapevines (Cook and Kishaba, 1956) and it is considered to be very reliable (Kliewer, 1991). The organ most often sampled on grapevines is the petiole; however, many growers may also sample the leaf blade. Generally, the petiole and blade will be analyzed separately and not as a single unit. In order to compare tissue analysis results from one year to the next it is advantageous to collect the samples at the same phenological growth stage. The sampling of petioles will occur most commonly at bloom. A second sampling date chosen by some will be at veraison (berry softening). The petioles (or blades) used for the sample at bloom will be taken opposite a cluster along the shoot. The petioles sampled at verasion will be obtained from leaves that are considered mature (fully expanded) and probably on the exterior of the canopy. Research conducted in California has shown that the analysis of the fruit at harvest and canes at pruning could also be used to assess the nutrient status of grapevines (Kliewer, 1991)....
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- Fall '10
- Grape, Thompson Seedless, petiole nitrate-N values, thompson seedless grapevines