Chilean cherries for export must resist long travel and storage periods, maintaining quality characteristics. Calcium is a very influential factor in the achievement of this objective; however, its transport to the fruit tends to be limited and is defined in few days.  

Chilean cherries for export must resist long travel and storage periods, maintaining quality characteristics. Calcium is a very influential factor in the achievement of this objective; however, its transport to the fruit tends to be limited and is defined in few days.

This component is an extraordinarily important mineral for the quality of cherries, above all their firmness, since among the main causes of softening and other associated disorders, a high concentration of nitrogen (N) is found, as well as low concentrations of calcium (Ca) in the fruit. 

From there it can be deduced that the probability of occurrence of those problems increase with a high relation of nitrogen/calcium in the fruit. Consequently, the management techniques should point to maintaining the concentration of N controlled and to maximize the concentration of Ca in fruit.

The main role of calcium is to preserve the integrity of the cytoplasmic membrane and confer resistance to the cellular wall, since it happens to be a main component of pectates (pectins), it is a part of the middle lamella between neighboring cells and they cement the union with each other.

The Ca coming from the roots is “loaded” towards the xylem vessels. In the xylem, the Ca is transported rapidly through the mass flow caused by the transpiratory current towards those transpiring organs. Since the leaves belong to the organs with more transpiration, the larger part of Ca will be directed towards them. If hydric stress is caused at this time, the leaf stomata closes, cutting off the water outflow via transpiration and thus stops the ascent of calcium, just like the rest of the minerals. Therefore water stress is directly related to nutritional stress.

Predisposing factors for softening:

–Varieties: Among the most prone are, for example, Early Burlat, Pigeon Heart, Lapins, Santina, Bing, Sweet Heart, Regina and Kordia.

–pH: In soils with values under 6, sub-acid or acidic, calcium salts form other more soluble molecules and they become susceptible to loss due to washing. This situation is more common in soils of the southern zone of Chile.

–Fertilization: With a high presence of cations competing with Ca, like potassium (K+), magnesium (Mg++) and ammonium (NH4+). This is easily avoidable, since the best time of application of said elements doesn’t coincide with Ca.

–Excess of vegetative development: (Many times related to the over-abundance of N) This is due to the Ca that moves through the transpirational stream, vegetative growth will promote the flow of Ca mainly to leaves and shoots to the detriment of fruit.

Opportunity: The time to accumulate Calcium

From setting until the fruit reaches a size of 5 to 8 mm, there are migrations of Ca towards them, because their maximum transpiration occurs in the initial phase of development. Migration may be incremented if the concentration of Ca of the xylem fluid is elevated, which reaches through the fertilization and the accumulation of good reserves.

After cherries reach 5-8 mm, xylem functionality drops substantially and the concentration of Ca begins to diminish in the fruits due to the dilution effect. As can be seen, the time available to accumulate calcium in them is short, no more than 10 to 15 days (depending upon the cultivation area).

The strategy to increase calcium flow towards the fruit must be focused from pre-blooming until the fruit reaches 5 to 8 mm in size, fertilizing strongly with Ca in the soil.

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This report was done based upon an article published in RedAgrícola (Agriculture Network) by Dr José Ignacio Covarrubias, specialist in plant nutrition and professor from the Agriculture Production Department of the Agronomic Science Falculty at Universidad de Chile (UCHILE).

For further information about the PTEC66647 Program Fruit Growing Center South contact Claudia Jorquera claudiajorquera@uchile.cl or Alejandra Vinagre maria.vinagre@uchile.cl