223-Interpreting Your Leaf Analysis Results

Fact Sheet No. 223, UMaine Extension No. 2093

Prepared by Lily Calderwood, Wild Blueberry Specialist, David E. Yarborough, Extension Blueberry Specialist, and John M. Smagula, Emeritus Professor of Horticulture, The University of Maine, Orono, ME 04469. Revised December 2020.

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 make 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 dropped down into the rhizome for winter storage. 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 the Wild Blueberry Fact Sheet, Improving Your Wild Blueberry Yields (PDF).

The growth of new shoots in the prune year is dependent on both stored carbohydrates 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. However, wild blueberries have 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 macronutrients with a description of their function in the plant and deficiency symptoms. 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 phosphorus 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 the way nitrogen and phosphorous are. 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 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. 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 above optimum may occur 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. Check the levels from your leaf nutrient report to ensure you are not exceeding the maximum amounts.

Nutrient Standards

The original levels of nutrient concentrations used in the past were from 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 the example on the Wild Blueberry Fact Sheet No. 222, Leaf and Soil Sampling Procedures).

Levels of Potassium or micronutrients will not have recommendations because we have not found that adding them increases yield. However, if the levels are below the minimum, adding micronutrients could be beneficial. If above the maximum, any fertilizer mixture with that specific micronutrient should not be added because excess nutrients 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 on the 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 take leaf samples from the field the year you apply the fertilizer.

Element	Santiago 2011
Foliar Nutrient Levels of Lowbush Blueberries* Standard Range
	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

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