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The olive tree has a behavior with respect to water very different from that of most crops, since it develops its greatest physiological efforts not in summer, but in spring and autumn.
Most of the cultivated plants come from climates in which rainfall occurs more or less frequently in summer, be it tropical, monsoon or Atlantic climates.
The Mediterranean climate as such is one in which rainfall is concentrated in the temperate and cold seasons, being very scarce in the warm season. Mediterranean climate plants have evolved to withstand summers with high temperatures and little soil moisture.
The vine comes from the Mediterranean climate, but it is a riverbank plant, which has evolved in environments of permanent edaphic humidity, hence it reacts very well to deep soils and to irrigation in summer.
Although almond and pistachio trees have a Mediterranean climate, in reality they have a climate with more steppe hues, with cold winters and irregular rainfall more distributed throughout the year than in the Mediterranean climate as such, for which they respond moderately well to summer watering.
The olive tree, however, evolved in climates of not very cold winters, with relatively rainy autumns and springs and ideal temperatures for plant development, the most adverse season being summer, when neither temperatures nor humidity accompany the physiology of the plant.
The olive tree must have guaranteed humidity in the soil, mainly in key physiological moments, not having much productive impact when there is excess moisture in the soil in periods of low physiological activity.
Key physiological moments
The key physiological moments in the olive tree are: sprouting, flowering and curdling.
Sprouting
The olive tree sprouts at the end of winter
Flowering
The olive tree blooms in late spring
Curdled
Early summer
First phase of fruit growth (cell division). Until the middle of summer.
The second phase of exponential growth of the fruit, with the accumulation of the oil, usually occurs at the end of summer, throughout the autumn and ceasing at the beginning of winter:
There will always be small variations that are produced by the variety, microclimate, soil, etc.
In years of medium to low loads, vegetative growth also occurs in autumn.
In winter, the metabolic activity of the olive tree is minimal although not null, since the solar radiation and the temperatures are low; soil moisture is not usually limiting.
In summer, solar radiation is high, exceeding the assimilation capacity.
Maximum daytime temperatures in summer frequently exceed physiological thresholds at which plants can produce biomass. In addition, the humidity of the soil is low, assuming a great metabolic effort for the roots, to extract the water that evapotranspiration demands from the aerial part.
The olive tree has evolved in the Mediterranean climate, and generally, it is also cultivated in the Mediterranean climate. Therefore, the irrigation in the olive tree must be understood based on the following premises:
- As a way to compensate for the high intra and interannual variability in rainfall in the Mediterranean climate.
- As a way of being able to withstand the great water demands of modern plantations with large volumes of canopy per hectare, due to a high number of olive trees per hectare.
Recommended frequency
To talk about the recommended frequency of irrigation in olive trees, we would say that the objective of irrigation would be to guarantee sufficient moisture in the soil, during key physiological moments, which occur mainly in spring and autumn.
In winter and summer, the soil has to have only a certain degree of humidity that does not cause the plant to become excessively dehydrated.
The response to olive tree irrigation is high in key physiological periods, even with low amounts of water provided in irrigation. There are large productive increases when small amounts of water are added at key physiological moments, but these productive increases with respect to the water supplied, decline dramatically when irrigation occurs outside of key physiological moments or large amounts of water are added: there comes a point in that not by more watering we are going to obtain greater production.
Irrigation in the olive grove, having the crop in the Mediterranean climate itself, must always be understood in combination with the rain and the humidity of the soil.
In winter, it is usually only necessary to water something in desert climates, to maintain minimum humidity.
In Mediterranean climates, if the irrigation system soaks a large percentage of the surface of the olive grove, and the soil has a large water storage capacity, as it is deep and clay loam, it may be interesting to water in winters that are very dry. to recharge the water reserves of the soil in the face of spring.
In spring, the olive tree has to be in conditions of hydration very close to the maximum.
In nature, a dry spring causes the olive tree to prepare for a summer of great water stress, significantly reducing vegetative growth and fruiting, to reduce future water demand.
Therefore, from an economic point of view, water stress in spring causes serious declines in production, which must be avoided at all costs.
In spring, the moisture content in the soil should be relatively constant and high.
Depending on the rainfall, type of soil in the olive grove and density of olive tree plantations, this will be the irrigation schedule.
In summer, as we have mentioned, in the olive grove it is necessary to maintain a sufficient moisture content in the soil so as not to cause great water stress in the plant, which causes the wrinkling of leaves and fruits.
When the olive grove is located in shallow soils, in areas with hot summers and with a large volume of canopy per hectare, they will require frequent and abundant watering.
On the other hand, in olive groves with deep soils, good rainfall in spring, not very hot summers and low crown volume per hectare, either because they are a very young plantation or because they are olive trees with a very wide frame and moderate crown sizes, there are times that in summer it is practically not necessary to water.
Olive tree showing strong water stress at the beginning of summer, when the fruit is in the initial phase of intense growth. The fruits do not develop the stone to their size, and although in autumn the olive tree receives an adequate supply of water, the harvest will be scarce since these fruits will never reach a good size.
Olives in mid-summer with a certain degree of dehydration. This hydric status at this time does not have a negative impact on production. At the end of summer when the olive tree is rehydrated, the development of the fruit will continue normally. It can be seen that the fruit is of a good size, because the hydration of the olive tree has been satisfactory in the initial growth phase of the fruit.
From the end of summer, in the Mediterranean climate, convective precipitations occur, which are colloquially known as “summer storms”. From these dates, the olive tree is predisposed to react energetically to a generous humidity in the soil, growing both fruits and shoots, depending on the load level.
From the end of summer, the hydric status of the olive tree should be similar to that of spring, since the highest growth of the fruit, oil accumulation and vegetative growth is taking place.
An important hydric stress, entails that the fruit does not fatten, which negatively impacts the production of the olive grove.
In autumns in which the precipitation does not appear, in late summer the waterings must be relatively generous.
Rainfed olive tree in a year in which the late summer rains were delayed, with the consequence of the senescence of the fruits as a vital survival strategy of the tree, which implies the total loss of the harvest. With irrigation we can avoid these situations.
When rains occur, irrigation should be resumed only if the olive tree begins to show symptoms of water stress again.
There are no specific guidelines and with closed irrigation dates in the olive grove.
The amount and distribution of irrigation will depend on:
- Climatology of the area in which the olive grove is located and of the year in question.
- Type of soil in which the olive grove is located.
- The type of irrigation installation: number of drippers per olive tree, flow rate, etc.
- Plantation crown volume.
Conclusion
It should be watered according to the hydric status of the olive tree, not according to the calendar, as can be the case in most crops.
As a summary, in autumn and spring, it is not advisable to allow levels of water stress in the olive tree, as they have a great productive impact.
In winter and summer, some water stress can be tolerated in the olive tree, and it will be watered accordingly. Irrigation in the olive tree should preferably be quite spaced in time, based on important irrigations of several hours, except in shallow soils.
