Vineyard Nutrient Management

Plant Tissue Testing Packages

   Vineyard fertility management is part of an overall vineyard management program where nutrient supply that is soil fertility and soil pH, nutrient demand (vine vigor) and nutrient uptake (root growth, rootstock) interact.  In addition to the gaseous elements of carbon, hydrogen, and oxygen, grapevines require several essential mineral elements to grow and produce fruit.  

   Although the mineral elements are needed in different quantities, each one plays an essential role in completing the vine’s life cycle.  Most vineyard soils in New York and Pennsylvania contain sufficient amounts of most of these elements, however they may not always be readily available.  

   It is the grower’s objective to increase the availability of naturally occurring soil nutrients and to supplement deficient nutrients when needed.  

SPECIFIC NUTRIENT DEFICIENCIES AND THEIR CORRECTION

Nitrogen

   When the soil nitrogen is the limiting factor to vine growth and production by inhibiting canopy fill (sunlight interception) and chlorophyll production (photosynthetic capacity), the addition of nitrogen fertilizer improves vine growth and production.  When nitrogen is not limiting, the addition of nitrogen fertilizer can be detrimental to quality of fruit production.  Excessive nitrogen through either organic or inorganic means can produce vines that are overly vigorous, which leads to internal canopy shading, reduction of fruit quality, and reduced bud formation.

   The major nitrogen source the vine uptakes, comes from the natural decomposition of organic matter in the soil and nitrogen fertilizers are supplemental to this. 

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Soil pH

   Soil pH has a prominent effect on the availability of several essential nutrients for grape production.  Low pH (5.0 or lower), affects nutrient availability and root growth.  As the pH decreases from 5.0 to 3.5, aluminum solubility increases.  High free aluminum precipitates phosphorus out of the soil solution, making it unavailable to the plant.  Aluminum also displaces calcium and magnesium, decreasing their availability.  Aluminum can also affect root growth and development by inhibiting cell division.

   High pH soils present a different set of nutritional circumstances for grapevine roots.  As the soil pH rises from 5.0 to 8.0, aluminum insolubility increases and removes it from the playing field which alleviates some of the phosphorus problems and increases the availability of calcium and magnesium.  However, iron also precipitates out of the soil limiting its availability.  

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Potassium

   The most common nutrient disorder found in the eastern US vineyards is potassium deficiency.  Soil testing is a tool for monitoring pH and estimating nutrient availability.  Since grapevine root systems can be spreading and or relatively deep, tissue sampling is an effective tool in determining the nutrient status of the vine.  Soil and tissue tests measure different aspects of vineyard nutrient status.  Together they are a very powerful combination.

   There are several factors that can influence potassium deficiency in the vineyard.  This can make interpreting and alleviating potassium deficiency difficult.

   Several factors can contribute to potassium deficiency in the vineyard.  Magnesium competition, there is a negative, non-linear relationship between potassium and magnesium fall-petiole concentrations.  If one goes up the other goes down, finding a balance between the two is the key to preventing deficiency of either one.  The greatest potassium deficiency risk comes in a dry year in a vineyard with a large crop load, poor weed management, and after an application of dolomitic limestone.  A potassium nutrition strategy that appears to be successful in high production vineyards is to maintain fall petiole potassium values near 2%.  The idea is to increase the vine potassium to the point that it can withstand a high crop in a dry year.

   Potassium functions in a number of regulatory roles in plant chemical processes, including carbohydrate production, protein synthesis, solute transport and the maintenance of plant water status.

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Magnesium

   Magnesium has several functions in the plant.  It is the central component of the chlorophyll molecule – the green pigment responsible for photosynthesis in green plants.  Magnesium also serves as an activator of a number of carbohydrate metabolism reactions. 

   Deficiency is usually expressed in mid-to late summer when basal (older) leaves develop intervienal chlorosis or yellowing.  Magnesium deficiency of red-fruited varieties can cause leaves to turn reddish rather than chlorotic.  Magnesium deficiency symptoms are usually confined to the older leaves except in cases of severe deficiency.

   Insufficient magnesium impairs protein synthesis and chlorophyll production which reduce photosynthesis and sugar production. 

   Grapevines express magnesium deficiency symptoms because they are not obtaining enough magnesium from the soil.  Magnesium accounts for approximately 0.25 to 0.75 percent of the dry weight of nondeficient, bloom-sampled grape petioles.   

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Boron

   Boron is an essential micronutrient.  Boron has regulatory roles in carbohydrate synthesis and cell division.  A deficiency can disrupt or kill cells in meristematic regions of plants (regions of active cell division such as shoot tips).  Boron deficiency also reduces pollen development and pollen fertility.  Reduced fruit set is thus a common occurrence with boron deficient vines.

   Boron deficiency symptoms are commonly confused with other vine disorders and must be confirmed with a tissue test.  The early season symptoms appear soon after bud break as retarded shot growth and in some cases, death to shoot tips.  Later in the spring the primary deficiency symptom is reduced fruit set.  Note that poor fruit set is not necessarily due to boron deficiency, poor weather during bloom, can reduce fruit set.

   Foliar symptoms begin as a yellowing between leaf veins and progress to browning and deaf to the area of the leaf.  Early season deficiency symptoms result in shoot tips that stop growing. 

   Grapevines are considered to have higher boron requirements than many other crops.  For bloomed-sampled vines, petioles containing less than 30 parts per million are marginally deficient, although clear boron deficiency symptoms may not appear until the boron level reaches 20 parts per million or less. 

   A soil pH less than 5.0 and or greater than 7.0 reduces the availability of boron.  Also if droughts intensify boron availability drops probably because the topsoil dries sooner than the sub-soil.

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Plant Tissue Analysis  

     Analyzing plant tissue provides an objective means of determining the nutrient status of grapevines.  Tissue analysis reveals the concentration of essential nutrients or elements absorbed by or within view tissues.  Tissue analysis indicates only the relative availability of nutrients, a high availability of a nutrient in the soil does not necessarily mean that the plant can extract enough of that nutrient to meet its needs.

     Specific recommendations for tissue sample collection depend on the grower’s objectives.  There are basically two reasons for having a plant tissue test conducted.  One is for the routine evaluation of nutrient status.  The second is to diagnose a particular problem associated with that plant.

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Routine Nutrient Status Evaluation

   The general nutrient status of vines should be evaluated annually.  This will help guage the response to applied fertilizer.  Also a plant tissue test will detect any deficiencies before they become visible. 

   Because the concentration of most essential nutrients varies throughout the growing season one might sample vines at different times throughout the growing season.  This will ensure the understanding of the change in each nutrient concentration as the plant matures.  Because plant nutrient concentrations change rapidly in the plant in the early part of the growing season it is important then to sample as close to bloom stage as possible.

   Sample each variety separately because nutrient concentrations may vary somewhat among varieties.  Collect 20 to 40 petioles from leaves located opposite the first or second flower cluster from the bottom of the shoot.  Petioles are the slender stems that attach the leaf blade to the shoot.  Collect no more than 1 or 2 petioles per vine.  Choose leaves that are exposed to sunlight and that are free from injury and diseases.  Immediately separate the petiole from the leaf and place in the plant tissue kit provided.  Send to Agri Analysis as soon as possible.

   Concentrations of certain elements do not necessarily indicate a problem.  For example, applications of fungicides that contain manganese, iron, or copper can elevate the test results for those elements. 

   Certain elements like potassium are best evaluated during late summer where bloom-time samples indicate questionable results.  Collect a second set of samples 70 to 100 days after bloom.  Collect 20 to 40 petioles from the youngest fully expanded leaves of well-exposed shoots. 

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