The following study developed by Avium’s R+D+i Department, reveals the phenological moments, the frequency of applications and the use of the correct technical dosage to achieve maximum efficiency in foliar applications of Calcium. The above always thinking about achieving a productive potential based on fruit quantity, measuring different indicators, such as Ca content in the fruit, dry matter, sugar content, fruit weight, etc.

When talking about such an attractive business as cherries, it is undoubtedly necessary to talk about what happens at a country level year after year. The recent cherry season in Chile closed with a record exportation of more than 352 thousand tons, representing an increase of 54.3% compared to last season. Despite breaking this record, the commercial results since mid-season were not as expected, mainly due to rumors about the alleged presence of Covid-19 in a box of Chilean fruit in China, which lowered demand and thus prices, hitting the sector hard and substantially damaging the sales of this product in the main market for this crop.

It is in these undesirable circumstances when the fruit must be prepared for long periods of permanence in containers in the different markets without being able to be opened or, rather, waiting miraculously for the demand for the product to rebound at once so that prices can normalize.

Facing such a scenario, we begin to ask ourselves: in what condition will our cherries be, or rather, we go further back, and we begin to question whether the management and/or nutrition strategies that were used during the season were adequate to withstand this type of problems. These are questions that we should ask ourselves permanently, and not depending on unprecedented circumstances to build a cherry of the highest quality and condition, always considering the optimum productive potential of the orchard.

Within this line of work, as R&D department, we have carried out studies about the participation of foliar Ca applications to discover the correct dosage, according to the adequate nutritional levels at harvest time, where we have been able to establish, in a preliminary way, the optimal nutritional content of cherries (Fig. 1).

These indexes, which are a reference guide, should be an important aspect when determining the strategies for the nutritional plan to be implemented during the season, considering that the fruit is the product that will finally be marketed, when it will be reflected how well the work was done during the season, being a kind of “final exam” for all of us who work in the industry.

Within the objectives of the last seasons for the Avium R&D team, studies have been conducted to improve the condition and quality of the fruit; this is in response to determine quantifiable indexes that help us to make objective decisions in the work and nutritional strategies in the field. Thus, in the 2018-2019 and 2019-20 seasons, research was conducted on foliar applications of Ca in two adult cultivars in a commercial cherry orchard in the central zone of Chile, where different foliar application strategies were established, according to the concentration of use of each product.

There are different opinions about the way to apply foliar products; should it be done in doses, expressed in liters ha-1 or at a use concentration normally expressed in liters hL-1? Our perspective, in which consistent results have been evidenced, is to always apply the product concentration per hectoliter, considering a minimum dose per hectare and adjusting the volume of coverage per hectare to the TRV (tree row volume), where we can determine the actual coverage required.

As a theoretical basis for the study, one of the hypotheses put forward is that the higher the concentration of solutes in a medium, in this case in the lamellar part of the young tissues, the greater the absorption of the solution by the osmotic potential gradient, and that these strategies are more conditioned by the phenological moments established early, rather than by the number of applications that could be made.

Calcium is an essential nutrient for the structural conformation of cell walls, providing integrity and cohesion to plant tissues; it also acts as a chemical messenger between different plant organs and tissues. An optimal availability of this element in the fruit makes it less susceptible to problems related to mechanical damage during handling, storage and transportation of the product.

The generality of applications in foliar programs in cherries start from the early stage, from the phenological stage of open cluster (OC), since it also physiologically participates in vital functions such as multiplication and natural elongation and there would be green spots that would allow the entry-assimilation of nutrients. The absorption of nutrients by young tissues and leaves is a mechanism that is still not entirely clear, however, there are studies that report that the greatest absorption is done by the underside of the leaf, where the density and presence of stomata would be determinant for the absorption of nutrients applied via the leaf, however, the mechanism is still not entirely clear.

Two baseline studies were established, the first (Table 1) in search of the use of the number of investigations and the concentration of product use. The second study (Table 3) was carried out to ratify the use of high doses (concentrations twice the recommended on each label), to see its real participation in the final quality of the fruit.

The studies were carried out on cvs. Regina and Skeena, both on Gisela® 6 rootstock, in an orchard with a density of 1,667 plants/ha and with a load of between 15,000 and 18,000 kg/ha for both varieties.

Experimental units and repetitions were normalized to the same load density (No. fruits/ASTT) to make them comparable with each other.

The application strategy of research 1 consisted of testing the use of a commercially available product, which for these purposes we will call “Calcium A”, being in treatment 1 (T1) the label concentration in five phenological stages, starting at the early stage of exposed florets up to the fall of the jacket.

Treatment 2 (T2), the same concentration as T1, but in ten applications, from the exposed shoot downward. Treatment 3 (T3) consisted of twice the concentration of T1. Treatment 4 (T4) was the program with a “Calcium B” at 300 cc hL-1 , according to the label of the commercial product used.

In this table, the different indexes measured can be identified, such as Total Ca, Soluble Ca and Bound Ca, all expressed in mg/100g; in addition, the percentage of Soluble and Bound Ca that participate in Total Ca can be observed.

In practical terms, according to Figure 1, an optimum index is that in which the total Ca content exceeds 10 mg/100g, being exceeded by T2 and T3 cv. Regina and at T1 and T3 in cv. Skeena. Technically, in both varieties, a better performance is shown in the applications at double label concentration over the rest (T3), as well as a greater amount of bound Ca (mg/100g) in both cultivars.

In the literature it can be found that there is a direct relationship between the fraction of calcium bound to the cell wall in the form of calcium pectates and the structural behavior of the tissues. There is a very marked nutritional condition with other indexes and that occurs regularly; we could say that more than 80% of the measurements are expressed in that the Ca / M. Dry / Soluble solids, have a high degree of relationship, and that we can see in the T2 and T3, in cv. Regina, where there is a significant difference in the indices of Dry matter and Soluble solids with respect to the other treatments, as we say internally: these parameters “talk very well with each other”.

To ratify the treatments at double the concentration of use according to the label, the following was proposed:

In investigation 2 a similar dynamic to the previous one can be observed, being “Calcium C” (T1) the orchard application, “Calcium D” in T2 corresponded to the label concentration of the product and T3 was twice the concentration of T2.

Table 4 shows the results obtained in the same varieties studied previously, with the difference that the applications were in five phenological stages for all treatments in research N°2.

The orchard program (T1), Calcium C, we can identify a lower content of Total Ca in the fruits, having a significant difference in favor of T2 and T3 (Calcium D and calcium D *2 ), which correspond to the application indicated on the label and double the label amount, respectively, compared to T1.

In treatments T2 and T3, in both varieties, statistical differences are obtained compared to the orchard program (T1), however, technically the treatment with the highest application concentration (T3) is the one that stands out with a higher total Ca content in the fruits.

Although in the measurement of cherry firmness measured with the Durofel (UD) cherry-meter it is not possible to determine clear differences in fruit firmness, from our perspective it is important to consider the percentage of dry fruit matter as an index that can help us to better conclude these results, since Durofel measurements are generally made when the fruit is in a higher degree of elasticity, due to the ambient temperature at which the fruit is harvested; the latter being one of the indexes used by companies to determine whether a fruit condition is suitable or not for a particular market. This is why it is very necessary to be able to understand the responses to different technical managements that are carried out in the orchard on the product that we are building, it is in this way that we will be able to continuously improve in order to reach an “optimal” fruit.

Conclusions:

The results of the high concentrations, which are at double the normal use, have a marked consistency regarding a greater accumulation of Ca in the fruit, and that could have determinant effects on the arrival of the fruit at destination.

Thus, research No. 1 first considered Ca applications at different phenological stages and at different concentrations, obtaining as a result a greater accumulation of Ca content in the fruit in the applications made from the exposed bunch to the fall of the jacket and with the highest concentrations used.

In addition, to ratify the results obtained in this research, a program of applications from exposed bunch to jacket fall was carried out as a N°2 research, consistently showing that early applications at doses with a higher concentration have a better response in the accumulation of Ca in cherry fruit at harvest.

Acknowledgments:

Agrícola Santa Ana del Rosario, Fundo Los Helechos.

Gabriel González, Ulises Tapia and Tristán Muñoz.

Technical Team Avium SpA