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There are two species of blueberries under cultivation:
Highbush Cranberry (Vaccinium Corymbosum)
Rabbiteye Cranberry (Vaccinium Ashei-Reade).

Fabric and time to sample

Tissue to be sampled: Recently expanded leaves of branches with fruits. The most advisable date for sampling is between December 15 and January 15.

Blueberries lack root hairs and their rooting is superficial. They are susceptible to both deficit and excess water; therefore the control of soil moisture is essential for the proper development of this plant.
Excessive fertilization produces a brown color on the leaves at the tips and edges of the blade; this species has a low fertilizer requirement.

Deficiency symptoms of the main nutrients and recommendations for their correction
The fertilizer needs of this species are very low, much lower than most fruit trees. The continuous applications of fertilizers, in low doses, have been more efficient than those made in high doses. In young blueberries, damage can be caused by excessive fertilizers, even if the doses are low; this can happen because its roots lack hairs
radicals. For this reason, it is not recommended to make localized applications.
Excess fertilizer has a depressing effect on this fruit tree, since this excess causes root damage.
The presence of a chlorosis can be induced by the lack of various nutrients; hence the identification of the causes must be determined through leaf analysis.

Deficiency

High doses of nitrogen (N) increase the levels of this element in the leaves, and may have detrimental effects on production (over 2.5% b.p.s). It is recommended that the application of this fertilizer is partialized during the season. This nutrient is used more annually and its consumption is in accordance with the age of the plant. The deficiency of this element produces a reduction in growth and the appearance of a chlorosis. As the interveinal chlorosis progresses, it is accentuated, there are burns on the edges and then abscission occurs. A not very vigorous plant presents pale colored leaves and there is early leaf drop, this may be due to deficiencies of nitrogen (N) - manganese (Mn) - iron (Fe) and to a lesser extent potassium (K) and boron (B). An excess of nitrogen (N) makes the plant more susceptible to frost.

Deficiency Correction

Ammonium nitrate (NH4NO3) is a nitrogen (N) carrier that is recommended to be used for its acidifying effect; alternatively, urea can be used in traditional irrigation. blueberry can absorb nitrogen (N), both in the form of ammonium (NH4 + ) as nitrate (NO3). Some researchers point out that the application of nitrogen halfway through the opening of the bud and the other to fall of the petals, this would increase the performance.

Deficiency

The deficiency of this element is of rare occurrence. In soils of the "Trumao" type, of that have variable free aluminum (Al) content, this is likely to occur. An excess of phosphorus (P) can induce a deficiency of iron (Fe) and with this the development is limited. of the plant. The deficiency is manifested by chlorosis. There is a very poor correlation between the phosphorus (P) of the leaves and that of the soil; not for this reason soil testing is recommended for this purpose. Newer leaves are smaller than normal, are greener, and growth is reduced.

Deficiency Correction

A phosphorus (P) carrier is used, which can be: triple superphosphate or ammonium orthophosphate. Alternatively, phosphoric acid can be incorporated into the technical irrigation system, as also monoammonium phosphate (MAP), monopotassium phosphate (MKP) or as urea phosphate.

Deficiency

The low levels of potassium (K) found in the foliage may be related to the acid soils. This element reduces its content with the age of the fruit tree. It also suffers variations according to the load that it presents; hence the older concentrations occur in young plants. There is a correlation between the potassium (K) of the leaves and that of the soil. High levels of potassium (K) in the soil aggravate the deficiency of magnesium (Mg), produced by its known antagonism between these elements.

Deficiency Correction

It should only be applied to this nutrient when its content shows deficiency. In this case it is used potassium sulfate (K2SO4) or potassium nitrate (KNO3) either applied to the soil or to the drip irrigation.

Symptoms of Toxicity

Blueberries, like other ericaceous species, are calcifugal or acidophilic and therefore they are adapted to grow in acidic soils with low calcium (Ca) contents; this is reflected in the low contents of this element in the leaf tissue. An excess can cause toxicity. The “Highbush” variety presents higher concentrations in the leaves than the “Rabbit Eye”.

Deficiency

The blueberry is a species that is adept at absorbing calcium (Ca). deficiency symptoms include a yellowing on the margins of the leaves, especially the young ones. Leaves terminals may present some yellowish-green spots. In Chile there have not been observed symptoms of this deficiency. Calcium (Ca) levels in soil have been observed to be related to pH levels present in it. Also the calcium content is related to the load of the tree and nitrogen fertilization. In plants with excessive vigor the content of this element becomes lower, which would be due to a dilution effect. The concentration of calcium (Ca) in the fruit influences its firmness, as well as the texture and harvest time. There is a close relationship between calcium (Ca) content and life fruit postharvest; especially its firmness. This can be increased with pre-applications. harvest, such as by immersing the fruit in a postharvest calcium (Ca) solution, with 0.5 - 0.8% calcium chloride (CaCI2).

Deficiency Correction

The calcium (Ca) level of the soil can be increased with applications of calcium sulphate or gypsum, this neutralizes the effect of interchangeable aluminum (“Trumaos”). Foliar applications of calcium chloride can produce phytotoxicity.

Deficiency

Magnesium (Mg) deficiencies are almost always associated with sandy soils and/or with low organic matter (OM) content. In general, magnesium (Mg) deficiency is closely related to a low cation exchange capacity in the soil. Excessive applications of potassium reduce the availability of magnesium (Mg), which is manifested through a chlorosis that appears late in the season. This appears as an interveinal reddening, in addition the leaves are curved, there is defoliation and some necrosis and growth is affected.

Deficiency Correction

This deficiency is corrected with the granulated application of Sulphomag to the soil and in fertigation with magnesium sulfate (MgSO4) also called Epsom salt or magnesium nitrate [Mg(NO3)2]. Alternatively sprays with magnesium nitrate (MgNO3) give good results, this It is made with young leaves.

Deficiency

Cranberry requires small amounts of zinc (Zn) hence deficiency symptoms be scarce. They grow in a medium in which zinc (Zn) is available (acid soils). Excessive applications of phosphorus (P) can induce a deficiency of zinc (Zn). deficiency of zinc (Zn) decreases the growth of the terminal leaves.

Deficiency Correction

With a zinc (Zn) carrier, early in the season.

Deficiency

Neutral or basic pH soils are prone to manganese deficiencies. To go down the pH, the content of manganese (Mn) usable by the plants increases significantly. Blueberry is a manganese (Mn) accumulator species, hence it is rare for it to occur deficiency. Levels up to 4,000 ppm (b.p.s) have been reported with no occurrence. toxicity. In blueberries, the lack of this element is manifested by chlorosis.

Deficiency Correction

To solve a manganese (Mn) deficiency, it is recommended to acidify the soil. Alternatively it can be sprayed with a product that carries this element, this with tender leaves.

Deficiency

As in the case of manganese, its availability is associated with pH, ​​presenting this deficiency preferably in neutral and alkaline soils. It is manifested by chlorosis. A high phosphorus content induces a deficiency of this element.

Deficiency Correction

It can be corrected through the modification of the pH, through the use of an acidifier, sulfuric acid (H2SO4), sulfur (S) or phosphoric acid (H3PO4) incorporated into technical irrigation. Alternatively an iron chelate could be used.

Deficiency

This affects flowering and therefore fruiting and consequently yield. HE produces a slight chlorosis. Excess produces burns and necrosis.

Deficiency Correction

Incorporate boric acid, sodium octoborate and/or borax into the irrigation system. Alternatively spray with a boron carrier (Solubor, Speedfol® B SP).

Other Considerations Depending on Soil Properties
pH
The development of the plant is lower in soils with a pH above 7; likewise, as occurs in soils with very low pH due to an effect of an excess of manganese (Mn). In alkaline pH soils development can be limited, which would be due to an excess absorption of sodium (Na) and due to limitations that this effect has on the absorption of elements such as phosphorus (P), zinc (Zn) and iron (Fe) mainly.
The best development of the plant, according to some authors, occurs with pH levels between 4.0 – 5.2 or 4.5 – 4.8. Most “Rabbit Eye” blueberry varieties thrive in soils with pH 4.0 – 6.0. pH levels above those indicated produce a nutritional imbalance, making iron chlorosis a common occurrence. When the pH is above these values, soil acidification proceeds, with sulfur (S) or sulfuric acid (H2SO4); this is recommended before planting. When using sulfur (S), as a precaution it must be mixed with the soil. As a general recommendation, every year it is convenient to check the pH of the soil, since the use of fertilizers can cause it to rise.

Organic Matter (OM)
In soils with a low OM content, the addition of pine sawdust, in the form of mulch, improves blueberry growth; especially in soils with pH above 6.0. This application of softwood sawdust should be supplemented with nitrogen (N), to stimulate microbial activity and achieve a faster decomposition of the sawdust and not run the risk of suffering “nitrogen starvation”.

Other Factors Influencing Nutrition
Light
The availability of light is particularly important in blueberries; This is how in the “Ojo de Conejo” variety, the percentage of colored fruits and their size is directly related to the amount of light that the crown receives.
Both the number of leaves and their spatial distribution are essential for a better interception of sunlight (winter and summer pruning). In plants, photosynthetic efficiency rarely exceeds 2%. Among the most important factors that affect it are an adequate supply of water and light related to the density of the crown, since the most shaded parts only achieve 50% to 60% of the maximum photosynthesis. The amount of fruit also affects it, since an increase in the photosynthesis rate is generally detected when the fruit-leaf ratio increases.
Water
The blueberry is very sensitive to the problems of water availability, both to the deficit and to the excess; hence, water can be a limiting factor on development and production.

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