General information about the olive tree
Olive trees constitute the most important crop of our country since the antiquity. It is inextricably linked to the growth and economic prosperity of the Hellenic region, and holds a special place within the Greek culture, as a symbol of knowledge, wisdom, abundance, peace, health, strength and beauty.
Today, olive trees cover 15% of the total cultivated surface and dominate amongst the arboricultural crops, occupying 77% of the tree areas.
Its excellent adaptation in the temperate Mediterranean climate, in combination with the accumulated experience of our producers, render Greece the 3rd bigger olive-producing country in the world, while the unique qualitative characteristics of Greek varieties put Greece in the 1st place worldwide in the production of extra virgin olive oil.
The olive tree grows and sets fruit in a large variety of soil types, even of low fertility. It is most productive however in loamy, sandy terrains of average composition that retain enough humidity and allow better exploitation of territorial humidity and nutritious elements.
For the achievement of satisfactory production in light sandy and gravel terrains additional surface irrigations are required during summer months and during olive setting period (August – September)
Heavy soils that retain water are inadequate for Olive cultivation, since olive trees suffer from rootrots, their output is decreased and the qualitative characteristics of the produced olive oil are undermined.
In regards to the chemical characteristics of the soil, the olive tree grows better in neutral or slightly alkaline terrains (pH 7-8), but can also endure in slightly acidic terrains. In pH values less than 5 and above 8.5 the growth and production of the crop are decreased.
The olive tree has an abundant radical system that utilizes territorial humidity in an excellent manner. Its leaves are leathery with thick waxy tegument, dense fluff and small sunk stomata in the underside. They limit transpiration, decrease the water loss and increase the plant’s resistance to the dry conditions, compared to other arboricultural crops.
Despite the resistibility of olive tree in the drought, the water is the main restrictive factor of olive production, more specifically:
- in regions with low annual precipitation (rainfall) levels (< 400mm)
- in regions with humid winter but dry summer
- in light sandy and gravel terrains
- in table olives
The olive trees present distinct stages during the annual vegetative cycle, where their requirements in water are maximized and the sufficiency of territorial humidity exerts a decisive effect on the quantity and quality of the final production:
- Stage of flower bud differentiation (February - March) – wintry rains
- Stage prior to blossoming (April - May) – wintry rains/irrigation in the event of arid winter
- Stage from fruitsetting until core hardening (May - June) - irrigation
- Olive oil production stage (August - September) - irrigation
Nutritious requirements of Olive trees
A rational fertilization program should substitute the nutritious elements that are removed from the soil due to olive collection and the annual lopping of the trees, and at the same time provide the essential fertilization units for the annual vegetation and blossoming of the trees.
The quantities of the nutritious elements that are removed from the tree each year due to defoliation, lopping and olive collection are presented in the following table:
|Elements that are removed for the production:
|100 Kg olive
|50 Kg timber
|50 Kg leaves
The harmonious supply of the trees with the elements above, in the appropriate quantity and proportion and in all of the critical stages of their development, provides nutritious balance to the culture, increased yields and high quality of the product.
Main nutritious elements of the Olive tree
Nitrogen is the most important and irreplaceable nutritious element for the vegetative growth and fruitation of the olive grove.
- it promotes vegetation, which is essential for the formation of the reproductive organs and fruit growth.
- it increases the number of flower buds that will give inflorescence
- it promotes the formation of perfect flowers, thereby increasing the fertilization and fruit setting
- it increases the fruit number and weight, thereby increasing the yield
- in combination with rational lopping and irrigation, it decreases alternate bearing of olive trees
The olive trees absorb large quantities of Nitrogen from the soil throughout the year, however they are particularly demanding and express real `' hunger'' for this element in specific stages of their annual vegetative and reproductive cycle.
- in the period of morphologic differentiation of flower buds (Feb. - Mar.)
- in the period of blossoming – fruit setting (Apr. - May)
- in the period of core hardening (Jun. - Jul.)
The sufficient supply of Nitrogen to the olive grove, during the stages described above, exerts a decisive effect on the quantity and quality of the final product.
Phosphorus is a component of important tree enzymes and proteins. It is directly or indirectly involved in a series of metabolic processes, and more specifically in those related to reproduction and energy transport. High concentrations of phosphorus are found in the young developing tissues.
From a functional perspective:
- It supplies the tree with the required energy for all its activities.
- It contributes to the root and timber formation.
- It contributes to the fruit setting, their strong retention and the production precocity.
Although in most Greek territories it does not constitute a restrictive factor for olive tree growth, phosphorus administration to the irrigated olive groves that are treated with rich Nitrogenous fertilizations and to table olive cultivars, constitutes a critical factor for the size, weight, precocity and qualitative characteristics of the fruit. In the rainfed olive groves and more specifically in soil rich in Calcium Carbonate (CaCO3) it should be administered it is granted in regular time intervals, so that the high levels of soil fertility are maintained.
Potassium, similar to Nitrogen, constitutes an irreplaceable element for olive trees. It presents high mobility within the tissues and subcellular structures, and participates in a plethora of physiological functions. It is implicated in the activation of many enzymes, in the production and transport of photosynthesis products, in water uptake and utilization and in the tree's water balance. As a result of its multidimensional function, its sufficiency in the olive tree:
- Increases the fruit size and weight
- Increases the oil content of the fruit
- Improves oil's qualitative characteristics
- Increases the resistance of trees to drought, frost and attacks from enemies and diseases
Olive tree has elevated annual needs in Potassium, particularly during the period of fruit growth and maturation, when more than 60% of the available Potassium migrates to the fruit.
In the oil producing cultivars it is essential to administer Potassium in equal quantities with that of Nitrogen, specifically in the year that increased fruit production is expected, so that the production of small fruit is avoided, the oil production is increased and the nutritious exhaustion of trees that leads to alternate bearing is decreased.
In table cultivars, the annual administration of Potassium is imposed, in order to achieve satisfactory production and improvement of the fruit's qualitative characteristics.
Boron is the most important trace element for Olive trees, and the most essential one for flower formation, and smooth development of fertilization and fruitsetting processes. It participates in the transport of carbohydrates within the tree, the synthesis of plant hormones, the growth of young tissues, the pollen production and germination and in the fruit growth. Boron deficiency constitutes the most frequent nutrient deficiency of the olive trees and directly affects the fertility of the olive grove, thereby dramatically decreasing the production.
Boron administration in the form of borax (250-400g. tree), or by using complex fertilizers that contain Boron, is considered essential in the basic fertilization of olive trees, as much in the humid acidic, as in the calcareous soil.
Foliar sprayings with Boron during the formation of new vegetation, and at the beginning of blossoming, have also a positive outcome.
Critical nutritious stages of Olive trees
Stage of flower bud differentiation (February - March)
The nutritious element sufficiency, and specifically Nitrogen, Potassium, Boron, and territorial humidity in this stage:
- creates surplus of carbohydrates and enhances flower bud differentiation
- accelerates the initiation of new vegetation that is essential for the formation of reproductive organs and fruit growth later on
- Increases the formation of annual shoots that are essential for next year's fruit production
The nutritious requirements of this period are covered by the timely application of basic fertilization in the winter (December - February)
Stage of Blossoming - Fruit setting (April - May)
Requirements of trees in nutritious elements and more specifically in Nitrogen, Phosphor and Boron are increased:
- Nitrogen sufficiency in this stage promotes the formation shaping of perfect flowers and increases fruit setting.
- Boron increases pollen germination and receptivity of the stigma, thereby increasing fertilization and fruit setting.
- Phosphorus provides the required energy for blossoming, fruit setting and initial fruit growth, thereby increasing the number of fruit per inflorescence.
The nutritious requirements of this period are covered by the basic fertilization of winter (December - February), in addition to foliar sprayings with Nitrogen and Boron that enhance the blossoming and fruit setting processes.
Stage of rapid fruit growth – core hardening (June - July)
Upon fruit setting completion, the growth of fruit core begins, and the requirements of the trees in Nitrogen and water and progressively all of the nutritious elements are increased, in order to climax until the hardening of the core.
- Large quantities of Nitrogen, Potassium and Phosphor migrate from the leaves to the fruit in order to cover the increased requirements of cell divisions.
- Nutritious sufficiency in this stage exerts a decisive effect on the final size of the fruit and oil production.
In irrigated olive groves the nutritious requirements of this period are covered with surface application of a Nitrogenous fertilizer in June.
Stage of slow flesh growth – oil production initiation (August – September)
After the core hardening, the flesh starts to grow, and olive oil accumulation in the fruit is progressively (from August) observed. During this stage requirement of trees in nutritious elements, and more specifically in Nitrogen and Potassium, are increased.
- Nitrogen sufficiency increases the fruit size and weight. Excessive Nitrogen during this period can decrease oil production and delay maturation.
- Potassium increases the oil content of the fruit and enhances the qualitative characteristics in table cultivars.
- Phosphorus causes maturation precocity, increases the weight and improves the coloration in table cultivars.
In table and in oil producing cultivar, in the year of increased production, the requirements of this period are satisfied by the application of Nitrogen-Potassium fertilization.
Olive tree Fertilization
During the wintry period December - February
It is sought to satisfy the basic needs in nutritious elements that are essential for the vegetation growth, the flower bud differentiation, the blossoming and fruit setting processes.
- In rainfed olive groves the entire quantity of fertilizer is administered in a single dose, with the basic fertilization.
- In irrigated olive groves and in table olives olive groves, the 2/3 of the total quantity of Nitrogen and Potassium and the entire quantity of Phosphorus are administered with the basic fertilization.
- The NH4 form of Nitrogen or the slow disengagement form of Nitrogen is preferred, due to the slow absorption rate, and avoidance of N losses with wastewater.
New shoots development
Initiation of blossoming
Before core hardening (June)
In irrigated olive groves for the reduction of fruit shedding, for fruit growth and development of sufficient vegetation for next year's fruit production, surface Nitrogenous fertilization (the rest 1/3 of required Nitrogen) and irrigation is applied, immediately after the completion of fruit setting (June).
Fertilizers such as Ammonium Sulphate or fertilizers with slow disengagement Nitrogen are preferred, because:
- they satisfy the needs of the culture until the beginning of maturation
- they do not invoke competition between vegetation – fruit setting that can lead to fruit shedding.
Completion of blossoming, Fruit setting
Fruit growth (10%)
Core hardening (30%)
Development of coloration (90%)
At the beginning of flesh growth –oil production (August)
In table cultivars where increase of qualitative characteristics is pursued, but also in oil producing varieties in the year of increased production, a second application of Nitrogen-Potassium fertilization at the beginning of flesh growth (August) is recommended, in addition to the nitrogenous fertilization of June.
Completion of blossoming, Fruit setting
Fruit growth (10%)
Core hardening (30%)
Development of coloration (90%)