Olive trees nowadays
Olive is one of the main species grown in the Mediterranean basin, especially in less-favored areas. However, olive oil which derives from olive tree fruits crush and often called “green gold”, not only because of its relatively high price compared to other oils used for human nutritional needs, but also because of the high nutritional value that characterizes it. In addition, the cost of all required work related to the production of olive oil remains high, even over 50% of the total cost of production. Therefore, it is still necessary to obtain a deeper knowledge about cultivation treatments in olive groves, which, as mentioned below, are mainly aimed at increasing the yield of olives and consequently the increased production of olive oil.
Factors affecting olive groves productivity
Although it is possible to cultivate olive trees even in areas characterized by the presence of arid climate, the provision of water, especially in critical periods such as hardening of the core, has a positive effect on the productivity of olive trees. More specifically, some scientists claim that Frantoio trees grown in places located on Mediterranean climate zone planted in rows at 5×3.9m distances and adequately irrigated are more efficient, at least in terms of the number of olives harvested and the amount of olive produced. However, some scientists claim that irrigation has only favored the number of olives harvested and their average fresh weight. Nevertheless, the same tension was not observed in the oil content of the olives, which was reduced compared to other interventions involving the irrigation of olive trees at different intervals throughout the experiment.
Similar results were presented by other researchers who studied the effect of deficient irrigation regimes on densely planted olive trees of the Arbequina variety. More specifically, these scientists claim that in conditions of moderate intensity of water stress, the amount of olive oil produced by the olive trees that underwent the above treatment increased significantly, declaring that the reason this phenomenon occurs is still unknown. Another important finding derived from the same scientists team is that the lack of irrigation of the olive trees generally accelerated the ripening of olive fruits, making it possible to harvest the olives early, thus avoiding their collection in late autumn, where they may appear in autumn.
Additionally, in Cordovil olive trees, it was observed that the productive potential of these trees decreased more sharply in years of reduced production, in cases where they were either irrigated only at critical stages of olive growth, or are not irrigated. However, the olive trees that were irrigated with an amount of water equal to 60% of the soil water capacity showed the highest production of olive oil in a period of 2 years compared to all other interventions.
In another variety of olive trees (Chemlali), some of which were irrigated with saline water, it was also observed that irrigation of these olive trees showed similar results to those mentioned above, in terms of reducing the oil content of the fruits and increasing the olive fruits produced. In addition, in trees of the same variety that were not irrigated, it was observed that their fruits showed the highest oil content throughout the experiments. Another interesting finding from the same research is that the composition of the olives may also be significantly affected by rainfall before the harvest season.
Also, the distribution of irrigation affected, in addition to the amount of olive oil produced and its various organoleptic characteristics. It has been observed that in Cordovil olive trees, the olive oil that had the best organoleptic characteristics derived from olive trees that were watered only at critical stages of olive tree growth (before flowering, at the beginning of the hardening period of the core) shortly before harvest.
Weather conditions, as is well known, affect both plant growth and productivity. For example, scientists searched about the efficiency of olive tree varieties in semi-mountainous areas located on places in the Mediterranean climate zone. In these conditions it has been observed that the production of olives and olive oil was influenced by both the variety and the year in which the trees are located (productive or not). Also, the production of olive fruits and olive oil was more strongly associated with the number of fruits, rather than their oil content. Therefore, scientists recommend the use of varieties of olive trees that produce a large number of olives and at the same time are characterized by high oil content.
In olive trees, the type of pruning that needs to be applied depends on many and varied factors. Moreover, scientific studies have been carried out, which refer to mechanical and manual practices of pruning olive trees where these are densely established in places located on the Mediterranean climate zone. More specifically, scientists report that the effects of pruning interventions on olive production are related to the variety of cultivated olive trees and possibly to their vigorousness. Also, in some varieties that were well adapted to the current climatic conditions, the amount of biomass produced due to pruning did not necessarily affect the amount of olives produced per tree.
Similar experiments conducted in Latin America reveal that in Arbequina olive trees irrigated with enough water to meet their needs, the reference year and the severity of the pruning affected the oil content of the fruit, as well as the dry weight of each fruit separately. In addition, the factors affecting the production of olives and olive oil were also influenced by the season when the pruning was carried out, since in the experimental plots that were pruned in the winter (removal of 75 cm from the perimeter of the tree), the production of olives and olive oil appeared increased. compared to other treatments. However, strict pruning of olive trees during the summer, according to the same scientists is not recommended, due to the reduced productivity of olive trees.
It is well known that both the composition of the soil and the addition of organic matter to it affect the efficiency of the cultivated species. It has been shown that in olive trees of the Chemlali variety in the treatment concerning the addition of composted materials in combination with the supply of saline irrigation water, was observed increased olive oil production, as well as the ratio of flesh to core in the fruits increased compared to other treatments.
In contrast, studies concerning the effect on addition of organic by-products (including the addition of sheep manure and the addition of municipal solid waste) in olive tree productivity found that statistically significant differences in olive production occurred only in the last year of the experiment, in experimental plots where sheep and those where green manure vermicompost was added.
From all the above, it is clearly understood that the yield of olive trees depends mainly on the characteristics of the variety cultivated. However, their productivity is affected both by abiotic factors (climatic conditions, soil) and by the extent of various cultivation cares carried out. More specifically, research aimed at finding the water needs of olive trees – which are related either to its quantity or to its distribution during the year in critical phases of olive fruit growth – can provide valuable information on production of olives and olive oil. Similarly, pruning season combined with pruning rigidity strongly affects the productivity of olive trees. Finally, another important factor that affects the production of olive trees is the composition of the added by-products, rich in organic matter, as they affect the amount of olives produced and consequently the amount of olive oil produced.
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