Calcium and its role in the cultivation of blueberries

Adequate firmness or better ripening rates are part of the benefits that Calcium (Ca) can deliver to blueberries. Although this has been a recurring theme among researchers and farmers, especially in those that focus on export, its excessive use can generate effects contrary to those desired.

Although the mineral propitiates the stabilization of tissues and membranes, it is a cofactor of some enzymes, influences the growth of the pollen tube -it is relevant in the fertilization of the flower- and regulates cell aging, one of its most important functions is that it can act as a messenger inside the seedling.

"The plant continuously receives various stimuli: salinity, toxicity, fungi, pH. Then, he has to react to such stimuli to survive. As it does? Through a mobilizing signal of calcium, mechanism that when activated, sends messages to different organs ", says Jorge Retamales, international consultant in berries.

Although the level of Ca required by blueberries to carry out this process is low, it is not easy to achieve it. This is due, to a large extent, to the fact that this species does not have radical hair, which leads to its absorption capacity being very limited. In fact, healthy plants usually present between 0,3% and 0,8% of this element at leaf level.

"Thus, beyond the foliar levels indicate that there is an adequate supply of mineral for these tissues, the nutrition of Ca to the fruit may be insufficient and affect its quality, ie its texture, firmness and rate of maturation," warns the advisor

The curious thing is that, according to various studies, the mineral is abundant in the soil, representing 3,6% of the earth's crust. In the Metropolitan, O'Higgins and Maule regions, for example, it has been determined that there are close to 2.000, 1.400 and 1.00 kilos of Ca per hectare, respectively.

Moreover, the studies also point out that most of the fruit species require between 5 and 40 milligrams of Ca per liter of soil solution, a figure that is far exceeded by the availability of calcium in the soil (80-140 milligrams per liter of soil solution).

With such abundance, why can blueberries present deficiencies at the fruit level? This is due, among other reasons, to the fact that Ca can interact with other minerals. Therefore, Retamales advises, in terms of nutrition, avoid the excesses of ammonium, magnesium and potassium, especially at the beginning of the season, which is when the largest amount of Ca will be absorbed by the roots to be translocated to the fruits.

In addition, advises to avoid excess nitrogen because it can cause an over accumulation of calcium in the buds to the detriment of the fruits. This management of nutrition includes maintaining an adequate level of boron, which will allow greater seed formation and, consequently, greater carry of Ca towards the fruit at the expense of the leaves.

The key is in the roots

The blueberry, according to Jorge Retamales, defines an order of priorities when delivering carbohydrates to their different parts. "First there is the fruit, then the buds and finally the roots. If there are enough carbohydrates, they will reach everyone. But if there is a shortage, the components with lower priority (roots) will be severely affected, "explains the researcher.

As an example the expert cites a study developed in Osorno, which shows that blueberries of the Emerald variety accumulate all the necessary Ca in the first 20 days after flowering, and then begin to lose it as the season progresses. The levels in the leaves, meanwhile, continue to increase.

This is because, in flowering and fruit set, the accumulation of Ca is indeed short on the part of the fruit. After this there is little additional accumulation. Therefore, a small fruit can have a good amount of Ca in proportion to its size. However, as it grows, if it is not able to absorb enough early in the season, the dilution of the mineral will generate problems in the firmness and will notably decrease its post-harvest life.

Different ways to apply calcium

To analyze the effectiveness of the different ways of applying calcium, Jorge Retamales cites the 2004 study conducted by Hanson and Berkheimer in Michigan (USA), who contrasted the application of this element as carbonate and calcium sulfate in AAA Jersey varieties, during 5 years.

In the case of the Hanson study, carried out in 1993, which aimed to see the effects of the immersion of the fruits in calcium chloride, in concentrations that oscillated between 0,25% and 4%, the results were different. Although the levels did not vary regardless of whether the immersion lasted 30 or 240 seconds, it was found that as the dose increased, the fruit acquired a saline taste.

But that is not all. According to Retamales, the immersion of the fruit in calcium could also affect the "bloom" or waxy covering of the fruit, whose presence is a factor of quality.

In his analysis, the international consultant also mentions Pablo Angeletti, who along with his team applied Ca to the soil to the 7, 14 and 21 days after the harvest in an orchard with varieties O'Neal and Bluecrop. This generated significant decreases in weight loss in relation to the control plants (to which Calcium was not applied).

Regarding the foliar application, Jorge Retamales comments on the results of several investigations carried out in the United States, which have ended up generating damage to new leaves. The funny thing, he says, is that this has happened with Calcium chloride at 0,08%, that is, a figure much lower than what exists in Chile (0,16%), where nothing has happened.

For the expert, making foliar applications with an environmental humidity with values ​​close to 70% or 80% can lead to the generation of damages seen in the United States. This, in turn, would explain why in Chile, where there is a low relative humidity, they have not occurred.

"In addition, apply foliar Ca when temperatures are above 25 ° C can also cause damage to the foliage, especially when the leaves are young," he warns.

In this regard, the consultant ensures that there are some contradictions between the trials, which in his opinion is due to the fact that the fruit represents less than 3% of the total exposed area of ​​the plant.

"This, in practice, means that it is very difficult to hit that small target. If you apply the Calcium foliar it is probable that the great majority arrives at the leaves. In addition, it should be considered that this is a little mobile element and will not translocate from the leaves to the fruit, "he warns.

Given this conclusion, the international adviser indicates that if early applications are made, when the fruit tends to represent more than 10% of the exposed surface of the plant, the possibility of the Ca going to the leaves will be somewhat lower. For this reason, it is recommended that the application of this element be carried out early in the season, more specifically between 20 and 30 days after settling.

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