By: Kirk Williams, Lecturer-Texas Tech University
Nutrient management is a critical practice to have a healthy and productive vineyard. Nutrition management in grapevines is a long-term process where nutrients can be added over time and the effects of these additions monitored over time as well. Grapevines do not require large amounts of nutrients and the nutrients can be added in response to needs identified by soil and tissue samples
While soil samples can give us great insight into the soil at a vineyard site they do have limitations in established vineyards. Grapevines have a deep and extensive root system that can exist at deeper depths than common soil testing equipment can collect from. Also, soil tests indicate relative availability and this level is not always reflected in nutrient status of the grapevine. Soil testing in vineyards should still be done in established vineyards but a sample every three to five years is adequate to understand what is happening in your vineyard soil.
In season nutrient management begins with assessing the nutritional status of the grapevine. The most common way of evaluating the current nutritional status of grapevines is through tissue analysis. Tissue samples can be taken at bloom time or at veraision. Sampling could also occur at both bloom time and veraision which can help you assess your in season nutrient management program. Areas where observable problems exist should be sampled separately from areas where growth is normal.
Tissue samples have historically been petioles but recently whole leaf samples have been utilized. Collecting a good representative sample is critical to getting accurate results. If you are collecting petioles, you will need 50 to 100 petioles from each block. If you are collecting leaves you will need 25 leaves per acre up to a maximum of 300 leaves per block. Many laboratories will wash tissue samples but that will require quick shipping.
So, it may make sense to wash your own samples. A few drops of phosphate free liquid detergent can be added to a basin with distilled water. Samples should then be rinsed with distilled water for no more than 10 seconds. Rinsing longer than 10 seconds may wash out some of the nutrients. Samples can be dried and then shipped to the lab for processing and testing.
Oftentimes soil and tissue tests are deemed precise because they are actual numbers determined by a lab. While they were determined by a lab, there are many factors that go into a fertility program for a vineyard. There are not many black or white, right or wrong answers in vineyard fertility management. There is only a continuum of possibilities all of which are impacted by the environmental conditions of the year, the soil, the microbial population in the soil, fertilizers applied, cover crop interactions as well rootstock and scion responses to all of the above.
For example, in an extremely dry year, even with adequate boron in the soil and foliar applied boron, your plant tissue samples may show you are short on boron. Low soil water status reduces boron release from organic matter and boron uptake through reduced boron transport that occurs by diffusion and mass flow to absorbing root surfaces. The next year, under normal soil moisture conditions, your tissue samples may show adequate boron even though you did not fertilize with boron.
Use the soil tests and tissue tests as guides over time for your fertility program but don’t focus too much on the actual numbers, focus on the trends. Also, don’t forget to use your eyes to see the impact of your fertility program.
Generally, nutrients needed in large quantities, such as Nitrogen and Potassium, are applied to the soil. Nutrients needed in small quantities such as zinc and boron can be effectively applied to the foliage of grapevines. We will focus on foliar fertilization for the rest of this article. Boron and zinc can impact fruit set if they are low and are recommended to applied prior to bloom. This timing is usually critical for prevention of many fungal diseases and these nutrients, if needed, can easily be added to a pre-bloom fungicide spray.
Each individual nutrient capabilities for mobility within the plant can impact how effective a foliar nutrient application is. Mobile nutrients such as nitrogen, magnesium, phosphorus and potassium are moved in the phloem from the older leaves towards the growing tip. Deficiency symptoms will therefore occur on the older leaves. Immobile nutrients, such as boron, calcium and iron, are not moved around in the phloem. Deficiency symptoms will occur in younger leaves near the shoot tip.
In addition to nutrient mobility within the plant, nutrients can differ in their absorption through the leaves. Rapidly absorbed nutrients include the urea form of nitrogen, potassium and zinc. Moderately absorbed nutrients include calcium, the sulfate form of sulfur, phosphorus, manganese and boron. Slowly absorbed nutrients include magnesium, copper, iron and molybdenum.
Zinc is a nutrient that is partially mobile and is rapidly absorbed through the leaves so it is a good candidate for foliar fertilization. In contrast, iron is immobile in the plant and is slowly absorbed through the leaves so Iron is a not a good candidate for foliar fertilization.
Best practices for foliar fertilization include application during the cooler parts of the day, including a high-quality surfactant, good coverage of the grapevine especially the undersides of leaves and applications to young actively growing tissue.
Nutrient management in grapevines is an important management tool in having a productive vineyard that produces high quality fruit. Regular tissue sampling is required year after year to get feedback on your nutrient management program to fine tune nutrient applications to each vineyard site. Foliar nutrient applications can be an effective management tool especially for micronutrients.
Kirk Williams is a lecturer in Viticulture at Texas Tech University and teaches the Texas Tech Viticulture Certificate program. He is also a commercial grape grower on the Texas High Plains. He can be contacted at kirk.w.williams@ttu.edu
Resources
Singer, S.D., Davenport, J.R., Hoheisel, G., & Moyer, M.M. 2018. Vineyard nutrient management in Washington State.
Western Plant Health Association. Western Fertilizer Handbook. 10th Edition. 2023. Waveland Press, Long Grove, IL
