Monitoring Grapevine Nutrition
Monitoring Grapevine Nutrition with Plant Tissue Tests
Dr. R. Paul Schreiner, Research Plant Physiologist, USDA-ARS
Dr. Patty Skinkis, Viticulture Extension Specialist, Oregon State University
Managing and understanding grapevine nutrition can be a daunting task. Mineral nutrients are important to the entire vine as they play vital roles in plant biochemistry. An effective nutrient management program for vineyards is intensive and requires good records of fertilizer and irrigation inputs, vigor assessment, yield and interpretation of soil and plant tissue testing.
Soil testing is generally not useful in predicting vine nutrient status due to a variety of issues, such as differences in nutrient uptake or requirements of different varieties, clones and rootstocks, differing irrigation and soil management practices, and the plasticity of vine roots to explore soils in different environments. In addition, grapevines can store significant quantities of some nutrients to overcome short term deficits of soil supply, and this ability increases with vine age. For example, more than 50% of the canopy N and P came from stored reserves in the roots and trunks of non-irrigated ‘Pinot noir’ vines at Oregon State University’s Woodhall Vineyard (Schreiner et al. 2006). Soil analysis is useful in monitoring changes over multiple years, including pH and soil organic matter that can impact nutrient supply in soil. Of course, soil analysis is necessary in determining potential vineyard planting sites. Yearly soil tests are not recommended for perennial crops.
Plant tissue testing is the preferred method of monitoring the nutritional health of your vineyard(s). Many winegrape growers collect petiole samples from their vineyards every year (or two) and send them to a testing lab for analysis. Quite often the lab results end up in a desk drawer unless something appears alarming. Nutrient testing can be more useful if consistent, representative samples are collected year to year. It is also important to understand and correctly interpret tissue analysis data.
What do tissue nutrient test results tell you?
The data you receive in a plant tissue analysis report is nutrient concentration data; it is the amount of each nutrient per amount of petiole or leaf blade mass. Many assume that nutrient concentrations equate to nutrient uptake. This is not always true. The only way to be sure about nutrient uptake is to monitor the content of nutrients (which equates to concentration x mass and accounts for growth differences). Rapid growth can dilute the concentration of nutrients in leaves and petioles. Tissue tests are much more meaningful to you as a grower if you also have some measure of plant growth near the time of sample collection. This can be as simple as a rough estimate of how close shoots are to the top wire at bloom. Results from tissue analysis are most useful when combined with other information from your site such as previous and current season’s growth, weather conditions, recent inputs to the vines (fertilizer, irrigation, tillage) and past experience with the particular vineyard or block.
Interpretation of tissue analysis results is not a simple process because plant mineral nutrition is complex. If an element appears to be deficient, closer inspection of the vines is warranted (looking carefully for signs of deficiency symptoms). If deficiency symptoms appear, detailed sampling and tissue analysis should be considered. Be sure to include samples from unaffected areas of the vineyard with the samples from affected vines to confirm a nutrient deficiency. Tissue test results indicate nutrient status of vines, and they can be effective in identifying extremes whether at levels of deficiency or toxicity. When samples are systematically collected over a period of years, tissue test results can be a valuable tool to manage the nutritional status of your vines and indicate approaching problems.
Issues to Consider When Implementing a Tissue Analysis Program
1) Be as consistent as possible with respect to vine phenology (growth stage) when collecting tissue samples for nutrient analysis. Nutrient concentrations in leaves and petioles alike can change rapidly during the growing season (see Figure 1). Each of the four data points in this figure represents phenological stages of full bloom, véraison, harvest, and leaf fall. Note that data in Figure 1 are from all leaves and petioles on vines (not just opposite cluster). The important thing to take from these data is that time of sample collection is critical for getting accurate data from year to year. This is clearly shown in this example by the P data which showed a very rapid decline from bloom to véraison.
2) Monitor the same areas within specific vineyards or blocks. For example, designate and flag specific rows within a block that are revisited yearly. This can vastly improve the consistency of tissue analysis. Such sampling may be more important in western Oregon hillside vineyards where we have recently begun to understand the great variability in soils.
3) If you would like to monitor large blocks with a single sample, then collect petiole or leaf blades in systematic way and be consistent from year to year. For example, collect one petiole or leaf blade from a typical vine located every five posts from every 20th row, avoiding rows close to border of the block.
4) Collect and submit separate samples from problem areas where you suspect that vines are weak or otherwise lag behind (i.e. low lying areas that may develop more slowly over the season due to cooler temperatures)
5) Determine which times you will sample. Sampling is often done at bloom and/or véraison. Generally, petiole samples taken at bloom give a good indication of micronutrient status. However, véraison sampling is more indicative of the status of macronutrients (N, P, K). In general, véraison or ripening samples are better to diagnose N, P and K problems because these elements are mobile within the plant and/or are at very high levels at bloom. Many people like collecting samples at bloom because then they believe they can correct problems in the current year. This is unlikely as nutrient analysis takes time, and results need to be interpreted correctly to warrant fertilizer applications. Note: the whole vine nutrient uptake study that was conducted at Woodhall vineyard in 2001-2002 showed peak N and P uptake occurs in Oregon dryland vineyards at bloom and declines thereafter (see Schreiner et al 2006). Therefore, it is not likely that one can affect the macronutrients in the current season; however, micronutrients deficiencies can be amended with foliar sprays.
6) Determine which tissue to sample: leaf blade vs. petiole. Generally, petiole samples give an indication of K, Cl and Na deficiencies/toxicities. Leaf blade samples give a much better indication of N than petiole samples, but also Mg, Zn, B, Ca, Cu, and Mn deficiencies/toxicities. Petiole samples are easier to handle and collect in large quantities which provide a good average for the block sampled. The leaf blade is the working organ of the plant and relates better to physiology of vines. Analyzing both leaf blades and petioles can be useful to diagnose certain issues and specific deficiencies/toxicities.
Collecting Tissue Samples
Bloom (60-70% capfall) – For petiole analysis, collect 60-100 petioles of leaves opposite a cluster. Cut off the leaf blades and rinse quickly in distilled water or tap water, blot dry, put in paper bags, and begin drying in an oven at 50-70 °C, if possible. If you cannot dry them, get the samples to the lab ASAP! For leaf blades, collect 20-40 (remove petiole), rinse in distilled water and blot dry on paper towels. You need to start drying the leaf blades shortly after collection because they mold much faster than petioles.
Veraison (50% of berries colored) – collect 60-100 petioles and/or leaf blades in pairs – one opposite cluster and one from a recently expanded leaf from each vine sampled. Treat as above.
Interpreting Tissue Nutrient Test Results
Table 1 provides a guide for interpreting tissue nutrient concentrations for grapevines grown in Oregon. The values in this table were derived from numerous sources and represents our current understanding for winegrapes. Remember–these values have not been determined for winegrapes grown at low yields.
1) Nitrogen: Surprisingly, N is the most limiting nutrient in vineyards across Oregon. Nitrogen is more limiting in southern and eastern Oregon vineyards where soils are lighter and have less organic matter. Nitrogen status must be interpreted with respect to vigor and assessment of the visual characteristics of the vine. If N appears to be deficient based on tissue analysis, it is not advisable to give N to vines with high vigor. Adding some N fertilizer or using N fixing cover crops should only be considered if vines have low vigor and low N levels upon analysis. Excessive nitrogen at bloom can cause problems with inflorescence necrosis. In addition, low must N levels are not always associated with low levels of N in the vine.
2) Phosphorus: In general P deficiency has not been a problem in Oregon vineyards even though soil P can be very low (thanks to mycorrhizal fungi!). However, given the importance of P to flower and fruit formation and differentiation, keep a close watch on P levels. Low P status in grapevines may be best diagnosed by comparing leaf and petiole P at véraison because P will generally occur at a similar or higher concentration in petioles compared to leaf blades when P is adequate.
3) Potassium: Low K levels can be a result of drought and/or over-cropping vines the previous season. Amendments of vineyard K levels must be approached with care. Grape clusters are a strong sink for K. If your vineyard is cropped to very low yields, it is easy to over apply K fertilizers, which may lead to increased pH in musts. Note: high K in musts can also be associated with vigorous, shaded canopies and can be corrected by better canopy management.
4) Boron: Oregon has had a history of low B due to low B levels in OR soils. As a result, many growers apply foliar sprays of B regularly. It is recommended to maintain these sprays at low doses to prevent toxicity.
5) Zinc: Oregon has had some issues with low Zn, particularly in sandy or clay soils, often associated with high Mg levels. Foliar sprays of Zn are applied in dormancy with a follow-up spring spray if deficiency is severe.
6) Iron: This should only be an issue on the east side of the Cascades where soil Fe availability can be very low. Fe is difficult to diagnose based on tissue tests. The form of Fe in the leaf is most important, and leaf size is often reduced when Fe is limiting. Low Fe is better diagnosed by a combination of interveinal leaf chlorosis (bleaching) and high soil pH.
View the online Grapevine Nutrition Module for more information!
The following references are good sources for more information on individual nutrient deficiency symptoms and more detailed discussion of the management and interpretation of tissue test results for individual nutrients:
Campbell A and Fey D. 2003. Soil Management and Grapevine Nutrition. In: Oregon Viticulture (Ed. Hellman E.) Oregon State University Press, Corvallis, OR.
Christensen P. 2000. Use of Tissue Analysis in Viticulture. UC Extension Publication NG10-00.
Coombe, B.G. and Dry P.R. 1988. Viticulture Practices. Winetitles. Underdale SA, Australia.
Gärtel W. 1996. Grapes. In: Nutrient Deficiencies & Toxicities in Crop Plants. (Ed. Bennett WF) American Phyophathological Society, St Paul, MN.
Hellman, E. 1997 Winegrape Fertilization Practices for Oregon (http://berrygrape.oregonstate.edu/winegrape-fertilization-practices-for-oregon/http)
Pearson R.C. and Goheen A.C. 1988. Compendium of Grape Diseases. American Phyophathological Society, St Paul, MN.
Schreiner R.P., Scagel C.F. and Baham J. 2006. Nutrient Uptake and Distribution in a Mature ‘Pinot noir’ vineyard. HortScience 41:336-345.