Cultivating Olive Trees. Nutrition – Part 3

When cultivating olive trees nutrition increases olive productivity and helps trees to thrive. Also, the olive tree is known as a hardy tree with low nutritional needs and the ability to survive even in an extreme environment with minimal care and maintenance. Even if there is no fertilization at all, olive trees could survive.

Olive trees require several nutrients to sustain their growth, particularly nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and boron (B) at most. In order to learn the nutritional status of soil and olive tree, the best method is to perform the soil analysis along with tree tissue analysis (i.e. leaf analysis). The outcome of these analyses provides valuable information on nutrients including deficiencies and helps to plan a great fertilization program.

Read on to learn more about olive trees’ nutrition, fertilization process, types of nutrients, and feeding techniques.

3.1. Preparation Prior Fertilization

When preparing to feed your olive trees, you may ask how much fertilizer the olive orchard need, what type of nutrients, and their ratio.

Well, there is no simple answer and standardization. The preparation of olive tree fertilization depends on the following factors:

• local environment
• climate
• effectiveness of the fertilizer composition
• fertilization technique

In order to prepare best prior to fertilization and assess the nutrient contents, the good practice is to perform the following analysis:

• soil chemistry
• plant tissue (i.e. leaf analysis)

As a result, these analyses will provide a status on both soil and olive trees that indicate the deficiency of nutrients if any, and the quantity to apply in the fertilization plans.

3.1.1. Olive Leaf Analysis

So what is olive leaf analysis? Leaf analysis is a trustworthy technique for determining the olive tree’s nutritional state.

The main nutrients in olive leaves vary depending on the below:

• olive cultivar
• soil
• climate of the cultivation area
• time of leaf sample for analysis
• pruning practices
• irrigation practices

Some regional research has identified correlations between the time of leaf sample, foliar nutrient content, and production quality (source).

The research says that during the flowering phase leaf analysis is more successful for less mobile nutrients (Ca, Mg, Zn, Fe). While during the winter season, leaf analysis better shows results for nutrients with higher mobility as N, P and K (source).

Generally, the nutrition (%) for nitrogen, phosphorus, and potassium on the leaf should be 3.5% divided, respectively, in 2.1 – 0.35 – 1.05 with a ratio of 6:1:3.

3.2. Olive Tree Fertilization Phases

3.2.1. First Phase (1^st – 3^rd Year)

During the first years of planting an olive orchard, it is crucial to encourage the olive tree’s fast canopy and root growth with fertilization. Because the olive tree’s vegetative processes predominates over fructification. As a result, the olive tree will be efficiently prepared for flowering and fruiting.

In this phase, nitrogen is the most essential macronutrient. While phospho-potassic fertilizers are less crucial now, keeping in mind that these nutrients were spread over the entire surface of the soil and buried deep with tillage when the ground was prepared.

3.2.2. Second Phase (After 5^th Year)

After the olive tree and its roots are well established and during the entire life of the tree, the purpose of fertilization is to encourage and maintain the olive yield. Simultaneously, to ensure the renewal of fruiting shoots and roots.

3.3. Olive Trees Nutrition Needs & Frequency

In profitable olive growing, olive trees’ nutrition needs depend on

• phenological stages
• the climate
• olive cultivar
• potential yield
• management of the olive orchard, such as the use of irrigation and soil grassing.

Due to these factors, fertilization planning cannot be addressed as a standard procedure, and numerous researchers present different assessments of the olive trees’ nourishment needs (source).

So one of the ways to calculate olive trees nutrition needs is to use the returning criteria of nutrients taken away with olive harvesting, pruned wood, and abscised leaves.

For example, an olive tree requires about 900 g of nitrogen, 200 g of phosphorus, and 1000 g of potassium for every 100 kg of olives it produces. Therefore due to losses from leaching, volatilization, fixing, and so on such quantity must be doubled or triplicated in fertilization planning.

Most of the quantity (2/3) is to be supplied at the end of winter before the development of new shoots and flowering. The remaining 1/3 during the flowering period until olive fruit set. It is recommended approx 500 – 1500g of nitrogen fertilizer for bearing olive tree, in accordance with the size of its canopy.

Phosphorus and potassium fertilizers must be repeated every 5 to 6 years. The quantity should be determined by the findings of soil and leaf analysis.

These fertilizers are often applied in autumn with doses of 200-400 units of potassium and 100-200 of phosphorus per hectare combined with an appropriate amount of organic matter (manure or compost) by burying them with shallow tillage.

Climate & Soil Conditions for Olive Orchard	Fertilization Frequency & Technique
Old or Dry-condition Raised Olive Orchard	Bi- or tri-annual phosphorus and potassium applications (applied after harvesting in combination with deep tillage for rainfall storage)
Young and Intense Olive Orchard	Annually at the end of winter with lighter tillage

Interesting to know:

In a typical olive orchard, olive trees nutrition is mostly done on a systematic basis by applying large quantities of fertilizers to the soil. However, this approach is not always correct and often unnecessary for olive trees. Also, it can be harmful to the environment due to groundwater pollution.

Olive tree growers frequently use an empirical approach when fertilizing olive trees, applying considerably more fertilizer than the olive actually needs (source).

3.4. Type of Nutrients and Their Effect

The use of the appropriate fertilizer at the right time increases efficiency and reduces the cost of fertilization, with a positive impact on olive fruit yield and oil content.

Fertilization can be differentiated into organic and mineral. The first one helps to enhance the soil’s physical properties, including its structure, porosity, permeability, tackiness, consistency, water retention, and pH. The second one feeds the trees.

Let’s look into the main nutrients required by olive trees for the best performance and look.

3.4.1. Nitrogen (N)

Nitrogen is fundamental for olive trees’ growth, both vegetative and flowering – fruit set production.  

Olive Tree	Nitrogen Effect
Young Olive Trees	Nitrogen is essential in growing processes because it contributes to the formation of proteins and amino acids
Mature Olive Trees	Nitrogen encourages the development of shoots. It is an essential condition for maintaining constant productivity and positively influence flower formation, fruit set, and fruit development, particularly in the early stages, up until the pit hardening

Usually, nitrogen is applied to the soil using urea, ammonium sulfate, or ammonium nitrate. Olive trees respond readily to nitrogen application if they grow in low-fertility soils and if soil moisture is not a restrictive factor.

Additionally, it can also be supplied with organic materials like feathers or blood meal, compost, or a leguminous cover crop.

Quantity of Nitrogen Needed for Olive Trees

Depending on soil fertility and moisture, the recommended dose of nitrogen application is approximately 500 – 1500 g for a bearing tree.

The water should be available during the time of nitrogen application, either rainfall or applied through the irrigation system. Also, most fertilizers containing nitrogen should be applied on the soil with rainfall or irrigation following in the next hours to avoid losses due to nitrogen evaporation in the form of ammonia.

Season to Apply Nitrogen for Olive Trees

The season of nitrogen application is strongly related to the olive flower induction and fruit set.

• Most of the quantity (2/3) is usually applied during the end of winter, before flower bud differentiation, and before new lateral shoot growth.
• The rest of the quantity (1/3) is applied during the flowering period (from the pre-flowering stage till the fruit set). Nitrogen can be applied either directly to the soil (pre-flowering period) or through a foliar application (mainly with urea, pre-flowering, and fruit set). As a result, the olive fruit set is significantly increased.

Nitrogen Deficiency

The following signs show nitrogen deficiency (source):

• reduced growth activity
• leaf yellowing
• low yield
• alternate bearing

3.4.2. Phosphorus (P)

Phosphorus plays a role in the growth process by being important for

• cell division
• formation of meristematic tissues (i.e. cells that have the ability to divide)
• fruit set, fruit growth, and maturation
• lignification of shoots (i.e. stage when shoots change consistency and color).

Phosphorus is typically applied to olive trees every two to three years. Even if an olive tree absorbs a relatively high amount of phosphate fertilizer, its effects take a very long time to become apparent. It is highly immobile in the soil, so it takes time for phosphorus to reach the rooting zone.

Phosphorus fertilizer is considered necessary in acid soils or soils with high amounts of calcium carbonate.

The most popular phosphate fertilizers are soluble phosphates, especially superphosphates that contain 35 – 45% phosphorus pentoxide, which is the form that trees can absorb. An acceptable level of phosphorus pentoxide in the soil, as determined by soil analysis, is 50–100 ppm.

Phosphorus Deficiency

Phosphorus deficiency is not common in olive tree existence. These are the signs:

• reddish or purplish color of the green parts of the tree
• causes metabolic issues for growth and fructification (i.e. the act of forming or producing fruit)
• delay in olive maturation

3.4.3. Potassium (K)

Potassium encourages the build-up of carbon hydrates like starch, which serve as a source of energy for metabolic processes.

Potassium controls the water consumption of the olive tree through an increase in water retention in the tissues and it also regulates transpiration (i.e. loss of water vapor through leaf pores).

In addition, potassium is an enzymatic activator that increases the tree’s tolerance to severe temperatures and to several fungal diseases and stimulates oil accumulation in the fruits.

Season to Apply Potassium to Olive Trees

High amounts of potassium are removed from the soil with olive fruit harvest and pruning, mostly in high-yield seasons. Regular potassium fertilization is required to maximize both yield and quality, especially in years with heavy yields.

Potassium is typically applied to the soil throughout the winter in order to gradually reach the rooting zone with the rainfall. In areas where the availability of water does not pose a problem, potassium application can be done during the end of winter.

Olive fruit is highly demanding during growth, which means that an additional amount of potassium should be applied in the years of heavy yield during the period of fruit growing, thus during mid-summer.

This application is better to be done using a foliar fertilizer, in order for potassium to be readily absorbed and translocated to the needing parts (sink) of the tree.

3.4.5. Other Macro Elements

After nitrogen, phosphorus, and potassium, other very important nutrients are magnesium and calcium.

Magnesium

Magnesium is an essential constituent of the chlorophyll molecule and plays a significant role in photosynthesis. Typically it is not taken into account when planning fertilization because it is already added in so many fertilizers.

Occasionally, olive tree orchards growing on sandy, neutral soil can show signs of magnesium deficiency. This shortage is remedied by magnesium sulfate-based fertilization.

Calcium

Calcium is essential to the growth of olive trees, because it is a necessary component of cell walls, contributes to the mechanical resistance of tissues, and works as an enzyme activator.

Deficiencies of calcium due to soil acidity can be modified with a sufficient lime supply as calcium carbonate.

Sulfur

Sulfur can be found in the organic matter of the soil and in plant amino acids like cystine, cysteine, and methionine.

Sulfur-containing fertilizers, such as ammonium or potassium sulfate, can correct any possible sulfur deficiencies.

3.4.6. Microelements

Iron, copper, zinc, manganese, molybdenum, and especially boron are essential microelements since they all have evolved a unique and exclusive role as enzymatic activators in the biochemical processes of olive trees.

These elements are found in olive tissues and have a very narrow window between their sufficiency and toxicity levels. So leaf tissue analysis gives excellent information in order to determine the toxicity or absence of these microelements.

Boron

Among all microelements, boron plays a major role in pollen development, fruit set, and tree productivity.

Apical chlorosis in leaves (i.e. yellowing of leaves caused by a lack of chlorophyll) is the first sign of boron deficiency, which is followed by necrosis and leaf drop. In the cases of a slight boron deficiency, flowers have lower fertility because of the rise of ovary abortion (source).

However, boron deficiency can be corrected through leaf fertilization during the pre-flowering stages extremely quickly and effectively. Most growers combine during that period a foliar fertilizer of boron along with urea and sometimes sea-weed extracts in order to achieve the highest olive yields.

Foliar applications (sprays) have had statistically significant effects on the yield and leaf boron contents; thus, 0.4% foliar application of sodium tetraborate was shown to be the most economic dose.

3.5. Fertilization Techniques

There are different types and techniques of fertilization:

• chemical (synthetic) fertilizers (NPK applied beneath the tree canopy projection, typically in the form of combined fertilizers)
• organic fertilizers (green and animal manures, leaves, compost, manufactured organic fertilizers)
• fertilization on the soil
• fertilization through the foliage
• fertilization through watering systems

Let’s look thoroughly at the following fertilization technique: on the soil, through the foliage, and through watering systems.

3.5.1. On the Soil

Fertilizers are typically applied to the soil.

Nitrogenous fertilizers, nitric, ureic, or ammoniac are used annually depending on the needs of the olive tree and the time of the intervention. Nitric fertilizers are easily soluble and have a quick effect, whereas ureic and ammoniac fertilizers have a longer-acting time and greater persistence.

The nitrogen amount usually provided is of 1kg nitrogen roughly equivalent to 5kg of ammonium sulfate, 3kg of ammonium nitrate, 4kg of calcium nitrate, or 2kg of urea.

The main applications of phosphorus and potassium are done prior to the plantation of the orchard due to the low mobility of these elements in the soil. Subsequent applications are made every 4 to 5 years in the fall on the soil.

3.5.2. Through Foliage

Fertilizers can also be applied through the foliage (leaves) of olive trees. This technique can be efficiently used to meet the needs of the olive trees in times of particular demands (short of microelements) or as an integration of soil fertilization in the various phenological phases.

It is considered to be a valid support to increase the nutrient levels and the olive yield, reducing competition among metabolic sinks (shoots, inflorescences, and fruits) and increasing nutrient absorption through the roots (source).

It quickly supplies nutrients, uses a low amount of fertilizer, can be paired with pesticide applications, and is ideal for olive trees that are fed by rain or when ground fertilizations would be ineffective owing to low soil humidity.

The foliage fertilization technique has many benefits, including:

• timely intervention
• nutrients are given at the point of highest need
• effectiveness in a short time
• ability to fully utilize the delivered substance

Numerous applications are needed for olive trees if only a foliage solution is used (source). Some results show that foliar fertilization cannot completely replace nutrition received through the roots, even though it allows a reduction in the amount of fertilizer that must be given to the soil (source).

Numerous researchers have studied the effectiveness of olive foliar nourishment, and successful results have been shown by using urea solution for specific nutrients (source).

Foliar application is beneficial to meet plant requirements with high efficiency since potassium is quickly absorbed and disseminated through leaf tissues (source). In order for phosphorus to be readily absorbed and translocated to the fruits for quality purposes it is given during summer fruit growth, and it is best applied as a foliar fertilizer.

3.5.3. Watering Systems

In irrigated olive orchards, it is possible to apply nutrients to the tree by watering systems (fertigation). The benefits of this method include the simplicity of application and the effectiveness of fertilizers, which can cut fertilizer requirements by up to 30% when compared to soil distribution.

Fertigation reduces the management costs related to procurement, transport, and distribution of fertilizers, enhancing their efficiency in order to provide the trees with a higher nutritional level, to maximize yield, oil production, and profitability.

Read Next

Cultivating Olive Trees: Soil – Part 1

Cultivating Olive Trees: Soil Management – Part 2

Cultivating Olive Trees: Irrigation – Part 4

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