Grapevines do not require large quantities of fertilizers. Compared to agronomic crops, on a per acre basis the amount of fertilizers necessary to maintain proper vineyard nutrition levels are relatively small. Whether you are a homeowner with a few vines or a commercial grape grower with several acres, a properly developed vineyard nutrition program will provide the nutrients needed in the amounts needed without applying excessive quantities of fertilizer. There are several ways to apply fertilizers to a vineyard and numerous materials, both inorganic and organic, that can be used, but regardless of the fertilizer material used or the manner in which is it supplied to the vineyard a good vineyard nutrition program should be based on monitoring the nutritional status of both the soil and the grapevines. This is done through a program of soil and tissue testing.
Developing a vineyard nutrition program begins before the vines are ever planted. Soil samples of the intended vineyard site should be taken a year in advance of planting and submitting for pH and nutrient level analysis. Once the soil pH and nutrient levels have been brought up to the soil testing lab's recommendations, no additional fertilization other than nitrogen applications should be needed for the first 3-4 years of the vineyard's existence. Levels of nutrients in the soil other than nitrogen do not rapidly decrease on their own and grapevines do not remove large quantities of nutrients other than nitrogen and potassium (the latter only after fruit production begins), so after the soil has been properly sampled and amended according to recommendations prior to planting soil sampling and analysis should be done every 2-3 years beginning with the first full crop. Because different grapevine cultivars (and different rootstocks if grafted grapevines are used) have varying abilities to remove nutrients from the soil, growers with blocks of different cultivars should collect separate soil samples from the individual blocks.
Soil analysis by itself does not tell the full story, though. Soil analysis tells you what nutrients are available in the soil for uptake, but does not tell you what the grapevine nutrient status is. Just because soil nutrient levels are adequate for healthy grapevine growth and productivity does not mean that the vines are removing and utilizing those nutrients in the quantities that they need. Several factors can contribute to this: excessive crop load, poor vine health, root damage from disease, nematodes, or phylloxera, excess competition from weeds, imbalances of nutrients in the soil (magnesium-potassium being a common example), poor root function in wet soils, inadequate nutrient solubility in dry soils, etc. To determine the nutrient status of the vine itself, tissue sampling and analysis should be conducted every year beginning in the first cropping year.
Several tissues can and have been used for tissue analysis of grapevines, but the most commonly used tissue in most labs today is the leaf petiole. Petiole samples are collected at one of two times during the growing season: for Vitis vinifera cultivars (Cabernet, Chardonnay, Merlot, etc.) they are commonly collected at bloom from leaves opposite the basal cluster. For native and hybrid cultivars they are commonly collected at veraison (the time when the immature berries in the cluster begin to change color and soften) from the Most Recently Matured Leaf (MRML) near the shoot tip (Figure 1). This will be the most recently fully-expanded leaf with the darker green color indicating maturity rather than the yellowish-green color of a young leaf. The optimum nutrient values for these two timings are very different for most nutrients and you should be aware which set of petiole nutrient value standards is utilized by the lab to which you send your sample(s). The Soil and Plant Testing Lab at MU uses the veraison-based standards commonly used in Midwestern viticulture (Table 1).
|Table 1. Grapevine Petiole Nutrient Levels from Veraison Samples|
|Elementª||Deficient||Below Normal||Normal||Above Normal||Excessive|
|ªValues may differ among species for optimal growth. Values from leaves will vary significantly. For petioles taken between July 15 to August 15.|
|Source: Midwest Small Fruit Pest Management Handbook. Ohio State Bul. 861.|
As with soil sampling, petiole samples should be collected separately for individual grapevine cultivars. As stated earlier, this is because they have differing capacities for uptake of different nutrients. If a single cultivar is grown on different rootstocks (or one block of a cultivar is grown on its own roots and another block of the same cultivar is grafted onto a rootstock) these should also be sampled separately. As with soil samples, very large blocks (greater than 10 acres) of a single cultivar should be broken up into 10-acre sub-blocks; if the block is less than 10-acres but is not uniform then take more than 1 sample based on differences in soil or topography (i.e. – slope versus hilltop). When collecting the petiole samples pull the sample leaf from the shoot and immediately remove the leaf blade, keeping only the petioles (Figure 2). Do not wait until you have collected several leaves to remove the leaf blades; while they are attached they are still transpiring and pulling nutrient-containing sap out of the petioles. Pull only one leaf per shoot and preferably no more than two leaves per vine. Avoid diseased, insect-damaged, or torn leaves and those that have been in more shaded areas of the vine canopy. Use only healthy, whole leaves that are in an area of the canopy where they are exposed to full sunlight. Avoid weak or excessively vigorous vines and pull samples from vines that are representative of the "average" level of vigor for that block or cultivar. A sample should consist of 100 petioles. Once the sample is completed it should be rinsed in distilled water, the petioles should be laid out to dry and then packaged in paper lunch bags. Avoid plastic ziplock or sandwich bags. Label the paper bag with information on cultivar, rootstock (if grafted), vineyard location, block (if more than 1), and date the sample was collected. Send the samples to the lab immediately; delays can decrease the accuracy of the results.
The utilization of a well-planned and consistent soil and petiole sampling program will yield important information on vine nutritional status. This information along with proper timing of application can maximize fertilizer use efficiency, vine performance, environmental protection, and vineyard profitability.
Regional grape growers can send petiole samples to the University of Missouri Soil and Plant Testing Lab in Columbia, MO. Their contact information is:
University of Missouri
Soil and Plant Testing Laboratory
23 Mumford Hall
Columbia, MO 65211
REVISED: October 2, 2015