Use Soil and Petiole Analyses to Plan Your Vineyard Nutrition Program
by Rick Dunst, Viticulturist, Double A Vineyards, Inc.
As harvest draws near, there is one more chance to determine the nutrient levels in your vineyard in order to maximize vineyard productivity and wine quality in the future – by taking soil and petiole samples and having them analyzed for their nutritional status. The combination of soil and petiole tests allows you to monitor the nutritional status of your vineyard soil, and also to determine which nutrients may be deficient in your vines. This information will allow you to plan your vineyard nutrition program for the future.
Most grape growers recognize the need to determine the nutritional status of their soil prior to planting. However, it is also important to monitor the nutritional status on a regular basis once the vineyard is bearing fruit in order to make adjustments in the vineyard fertilization program. At a minimum, soil and petiole tests should be taken every three years to gauge vineyard nutrient levels so that any deficiencies can be corrected with supplemental fertilizer applications.
Soil tests can be collected any time of the year it is convenient, but researchers have developed two growth stages to collect and analyze petiole samples to monitor vine nutrient status – during bloom, and in the period between veraison (initial fruit softening and/or coloring at approximately 7° brix) and harvest. Bloom petiole sampling is preferable if poor fruit set has been a problem, especially in identifying nutrient deficiencies including boron and zinc. Many growers find themselves overwhelmed with vineyard tasks during bloom, and petiole samples taken after veraison but before harvest can be useful to determine the status of most nutrient levels in your vineyard. Deficiencies of key nutrients such as potassium and magnesium are readily identified from grapevine petiole samples, and deficiencies can be corrected with application of appropriate soil amendments.
HOW TO COLLECT SAMPLES
As mentioned, soil samples can be collected any time of the year, but it is most useful for the person making the interpretations to have access to both soil and petiole data. Collect soil from several locations in a vineyard block with uniform soil. If there is more than one soil type in a vineyard block, you should sample each soil separately so that you can treat them differently, if necessary. Each sample should consist of at least 15 sub samples to a depth of 8”. A soil core sampler or small auger (ca. 1” diameter) can be used. Air dry the sample, mix it up, fill the sample bag provided with the kit, and mail to the lab that is analyzing the sample.
Petiole samples can be collected from bearing vines at either bloom, or between veraison and harvest. The petiole is the leaf stem between the green shoot and the leaf. Samples should be collected from fruit-bearing shoots and should consist of 60-100 petioles. If samples are collected during bloom, collect them in the fruiting zone (leaves opposite blooming clusters). If samples are collected prior to harvest, collect the petioles from the most recently matured leaf (RML) on fruit-bearing shoots. Start at the shoot tip and work back to the first full-sized leaf which is the RML. On some varieties (like Concord) this is the first leaf on the shoot that shows some browning on the bottom side of the leaf. On VSP-trained vines with shoot hedging, sample from the upper part of the canopy a few leaves below where the shoot has been tipped. Once the petioles have been collected, they should be washed with mild detergent, rinsed with clean water, and air-dried. When dry, fill the sample bag provided with the kit and mail to the lab analyzing the sample.
WHERE TO SEND SAMPLES FOR ANALYSIS AND INTERPRETATION
Many Universities offer soil and petiole analysis through their Extension programs. A&L Laboratories also offers this service. Another option is purchasing soil and petiole kits through Militello Farm Supply, Inc. In the latter case, you can purchase kits at www.militellofarmsupply.com, collect the samples and send them to A&L Labs. The results will be sent directly to our viticulturist (that’s me) who will provide a copy of the results and interpret the analyses and make fertilization recommendations based on them. Regardless of where you send your samples for analysis, we are willing to offer our interpretation of the results to help you maximize your vineyard productivity and fruit and wine quality.
Further information in obtaining soil and petiole analysis kits can be found at:
Militello Farm Supply, Inc.