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Cooperative Extension: Maine Wild Blueberries


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Production - 223-Interpreting Your Leaf Analysis Results

Fact Sheet No. 223, UMaine Extension No. 2093 (PDF)

Prepared by David E. Yarborough, Extension Blueberry Specialist, and John M. Smagula, Emeritus Professor of Horticulture, The University of Maine, Orono, ME 04469.  (Revised January 2013)

The wild blueberry is a slow growing woody plant.  It spreads by means of an underground horizontal stem called a rhizome.  The rhizome also serves as a storage organ for food reserves and nutrients, such as nitrogen.  The rhizome and root system makes up about 70% of the mature plant; about 30% of the plant is seen as shoots above ground.  When plants are pruned after leaf drop when dormant, most of the reserve food made in the leaves and shoots has been moved to the rhizome. . Recent research indicates higher levels of fertilizer will improve yields if other limiting factors such as having adequate pollination, protection from disease and insect damage and adequate moisture from irrigation are provided, see Wild Blueberry Fact Sheet on Improving Your Wild Blueberry Yields (PDF).

Growth of then new shoots the year following pruning is dependent on both the stored food and nutrients and available nutrients in the soil.  The roots that develop on the wild blueberry rhizome are not as fine as many other plants and lack root hairs but wild blueberries have a symbiotic fungi associated with their roots.  The thread-like body of the fungi extends into the soil and serves to extract nutrients that would be unavailable and take them into the plant root and rhizome. Wild blueberries need a balance of nutrients to remain healthy and productive. The following is a list of maconutrients with a description of their function in the plant and deficiency symptoms but decreases in yield will occur well before the concentrations that result in deficiency symptoms.

Macronutrients

Nitrogen

Nitrogen (N) is one of the three “major” nutrients needed in larger amounts to support good plant growth.  Plants use nitrogen to form amino acids needed in the formation of protein.  Nitrogen is also required in the formation of chlorophyll.  It governs, to a certain extent, the use of other nutrients and it encourages vegetative growth of the plant. However, if too much nitrogen is applied, a lack of magnesium (Mg) and calcium (Ca) might develop, and excessive vegetative growth may lead to increased winter injury and lower yields.

Deficiency Symptoms

Lack of adequate nitrogen reduces the formation of chlorophyll, which results in pale or yellow green leaves (chlorosis).  The last green to disappear is along the midrib.  Since nitrogen is “mobile”, the deficiency symptoms first appear in the older leaves.  Reddish tints gradually appear at the leaf margins and spread toward the midrib or central vein.  In advanced stages, all leaves develop a deep red coloration.  Defoliation occurs in severe nitrogen shortage.  Leaves are small and overall growth is markedly reduced.

Phosphorus

Phosphorous (P) is used to store and transfer energy within the plant.  It is used in forming nucleic acids (DNA, RNA). Phosphorous stimulates early growth and flowering, promotes fruiting and seed production, encourages root development and balances the effects of excess nitrogen.  It also stimulates more vigorous plant growth.  Young growing parts contain considerable amounts of phosphorous.  The efficiency of phosphorous uptake seems to increase in the presence of nitrogen.

Deficiency Symptoms

Deficiency symptoms for phosphorous are not as obvious as those of nitrogen.  Growth is reduced and foliage is dark green and abnormally small.  In advanced stages, large patches of purple appear in the interveinal areas.

Potassium

Potassium (K) remains in tissues in ionic form and is not used in the synthesis of new compounds as are nitrogen and phosphorous.  Potassium is mobile in plants and tends to move from older to younger, more active growing tissue.  Potassium seems to be important in the formation of proteins, carbohydrates (sugar and starch), and chlorophyll.  It is necessary for the translocation of sugars and the formation of starch.  Potassium stimulates root growth and improves size and quality of fruit.

Deficiency Symptoms

Potassium deficiency symptoms first appear as interveinal chlorosis of the youngest leaves.  In advanced stages, the leaf margins turn red and subsequently develop into a marginal leaf scorch (dry, dead tissue) starting at the tip of the leaf.

Micronutrients

Micronutrients are those nutrients which are essential, but only required in very minute amounts, and descriptions of deficiency symptoms were developed by withholding the essential elements in greenhouse studies, so these symptoms would be very rare to see in the field. A high soil pH greater than 5.5 could result in Iron (Fe) or Manganese (Mn) symptoms of interveinal chlorosis similar to Potassium symptoms. Wild Blueberries tend to selectively accumulate Mn so high levels that the optimal may be obtained and are not a problem. However, other micronutrients such as boron (B) and copper (Cu) can injure plants if applied at higher amounts than necessary for plant growth and can cause extensive damage to blueberries, so check the levels from your leaf nutrient report to insure you are not exceeding the maximum amounts.

Nutrient Standards

The original levels of nutrient concentrations we used in the past were reported by Trevett in 1972.  These standards have been updated from work reported by Santiago in 2011 (Table 1).  The macronutrients N and P are slightly higher while the micronutrients Fe and Zinc (Zn) are now slightly lower.  These values will help you evaluate the nutritional status of the blueberry plants in your fields.  If the concentrations of Nitrogen or Phosphorus from your blueberry leaf samples are below the satisfactory level you should refer to the recommendations provided by the University of Maine Wild blueberry foliar analysis report (see example in Wild Blueberry Fact Sheet No. 222, Leaf and Soil Sampling Procedures).

Levels of Potassium or the micronutrients will not have recommendations because we have not found a yield increase by adding these nutrients.  However, if the levels are below the minimum then adding micronutrients could be beneficial but if above the maximum then any fertilizer mixture with that micronutrient should not be added because these nutrients such can be toxic to blueberries if too much is applied.  

Procedures for obtaining and submitting leaf samples for the Wild blueberry foliar analysis report are found in Wild Blueberry Fact Sheet No. 222, Leaf and Soil Sampling Procedures.  

To verify that the fertilizer application has raised the levels to the optimum level you should also take leaf samples from the field the year you apply the fertilizer.

Foliar Nutrient Levels of Lowbush Blueberries*
Standard Range
Element Santiago 2011  
  MIN MAX Optimum
Nitrogen (N) 1.55% 1.85% 1.76%
Phosphorous (P) 0.111% 0.143% 0.136%
Potassium (K) 0.31% 0.56% 0.44%
Calcium (Ca) 0.31% 0.40% 0.38%
Magnesium (Mg) 0.16% 0.18% 0.17%
Boron (B) 2 ppm 44 ppm 23 ppm
Iron (Fe) 34 ppm 37 ppm 35 ppm
Manganese (Mn) 710 ppm 2637 ppm 963 ppm
Zinc (Zn) 10 ppm 15 ppm 13 ppm
Copper (Cu) 3 ppm 6 ppm 4 ppm
Molybdenum (Mo)* 1.20 ppm 3.30 ppm 0.33 ppm
Aluminum (Al) 98 ppm 289 ppm 179 ppm
Sources:  Santiago 2011 MS Thesis University of Maine, Orono * Trevett 1972

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 1987, 2013
Published and distributed in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, by the University of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the USDA provide equal opportunities in programs and employment. Call 800.287.0274 or TDD 800.287.8957 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.

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Contact Information

Cooperative Extension: Maine Wild Blueberries
5741 Libby Hall
Orono, Maine 04469-5741
Phone: 207.581.3188, 800.287.0274 (in Maine) or 800.287.8957 (TDD)E-mail: extension@maine.edu
The University of Maine
Orono, Maine 04469
207.581.1110
A Member of the University of Maine System