The olive tree is one of the most ancient cultivated fruit trees and the use of olives has been ascertained in the late Stone Age at the Kfar Samirin site in Israel. Cultivated olive (Olea europaea L.) was developed by domesticating wild olives, Olea europaea L. subsp. oleaster Negodi, with which it shares close genetic affinities. The crop was known to all ancient Mediterranean civilizations, and it probably originated independently in several different areas. The olive variety we know today is the result of selective breeding which began about 6,000 years ago when Syrian and Palestinian farmers, and probably also those in the vast area stretching from the Southern Caucasus to the Iranian plateaus, managed to obtain one or more varieties with fruits containing plenty of oil, but without the thorns of the wild variety. Currently, the species is cultivated in all the countries of the Mediterranean, as well as in Australia, New Zealand, North and South America and South Africa. The 10 most-producing countries, according to the Food and Agriculture Organization, are all located in the Mediterranean region and produce 95% of the world’s olives.
The olive tree is part of the flowering plants of the Oleaceae. Once planted, it starts to have fruits around the third/fourth year, while full production in reached only around the ninth/tenth year. It is very long lasting and can even reach 1000 years, when growing advantageous climate conditions. Its roots grow casually, superficially (never deeper than 60/ cm) and expanded. Its trunk has a grey/dark-grey coloured cortex and is typically gnarled and twisted, while the actual wood is hard and heavy. Each year, its stump features several suckers at the base. Its crown is conical including pendulous (parallel to the trunk) or pattent (that is horizontal towards the trunk) fruit branches. It is a perennial evergreen plant and grows less during the winter period. It comes with simple, coriaceous leaves featuring an oval/lanceolate shape with silvery/white colour as for the lower part, and dark green for the upper part. It produces hermaphroditic flowers grouped in cluster blooming, called “inflorescences”. Its fruit (a drupe) is ellipsoid or ovoid depending on plant variety, climate and cultivation technique.
The development cycle of the olive tree, like any other plant, is ruled by the seasons. After remaining asleep during the winter, in spring this tree shows its splendor and begins to wake up from its lethargy. Then it starts its journey through the phenological stages, which will culminate in autumn with the arrival of the fruits.
The growth of all plants occurs from the appearance of the buds. In the case of the olive tree, sprouting begins at the end of winter and in this phase the buds will change to buds of two types, vegetative buds and flower buds, which form floral clusters.
In this stage the olive tree shows a great amount of flowers whose objective is to be fertilized thus becoming new fruits. In the end just 1-2% of flowers will become fruits.
Once the flowering is over, they are released from their petals when fertilized and thus begins the beginning of a new olive. During fruit set, a fall occurs, made naturally by the tree, leaving only those fruits that will be able to feed.
The fruit bone begins to harden, until it reaches a definitive size and an intense green color and will accumulate reserves until it reaches maturity.
It is the stage in which the fruit changes color, finding at first some olives that will lose the green tone, changing to a yellowish or pink tone, until reaching an intense garnet or jet black tone.
Commercial olive production generally occurs in two belts around the world, between 30° and 45° N latitude and between 30° and 45° S, where the climatic requirements for growth and fruitfulness can be found. Olive varieties do not come true from seed. Seedlings generally produce inferior fruit and must be budded or grafted to one of the named varieties. Olives can be propagated by cuttings, either by hardwood cuttings set in the nursery row in the spring or by small, leafy cuttings rooted under mist sprays in a propagating frame. The trees start bearing in 4 to 8 years, but full production is not reached for 15 or 20 years. The ideal climate for the cultivated olive tree is characterized by a warm and sunny summer and a cold and rainy winter, but where the temperatures never drop below -10 ° C, which has proven lethal to the olive tree’s cells. Since the olive is an anemophilous species, areas with high humidity levels during the flowering period are not suitable. The soil needs are modest. In general, the olive tree prefers loose or medium-textured, fresh and well-drained soils. It also grows well on coarse or shallow soils, with outcropping rocks. On the other hand, it suffers in heavy soils and subject to stagnation. Regarding chemical fertility, it also adapts to poor soils and with a reaction far from neutral (acid soils and calcareous soils) up to tolerate pH values of 8.5-9. Among fruit trees it is one of the most tolerant species to salinity, therefore it can also be grown near the coast.
Even if olive tree is considered a particularly rustic plant, fertilization is essential for two main reasons: as a source of restoration of soil fertility and as a source of elements necessary for the plant to grow and produce fruit. In fact, nutrient deficiencies cause a state of stress in plants which negatively affects production and vegetative growth throughout the year. The most important elements of fertilization are nitrogen, phosphorus and potassium (NPK); however, the micronutrients should not be overlooked, and among these in particular Zinc, Boron, Magnesium and Sulfur.
The nutrient requirement of the plant changes according to the production phase; therefore the fertilization of planting, breeding and production is distinguished.
– Planting: in this phase, the contribution of organic matter is of considerable importance as a reserve source for the young seedlings, particularly useful in such a difficult moment as the transplant crisis;
– 1° and 2° years: the main element in this phase is nitrogen which facilitates the growth of the plant;
– Production: to achieve high quantitative-qualitative productions it is essential to replenish the nutritional elements taken from the plant, in a balanced context (NPK).
The crop also benefits from the application of foliar fertilizers to integrate soil fertilization, especially to provide microelements like boron. Products with a biostimulant action can improve the availability of nutrients, increase the yield from a quantitative and qualitative standpoint and reduce the negative impact of climatic stresses. The application of biostimulants increases the environmental and economic sustainability of the production system. The application of biostimulants in olive tree before flowering and fruit set allows the formation of a greater quantity of fruits.
Before vegetative growth
After fruit set