Crop Guide: Olive Tree Fertilizer Recommendations

As noted above, olive trees are quite tolerant when it comes to soil pH. When soils are overly acidic, lime is commonly used to correct the pH. The amount required varies with soil texture. The approximate amount of finely ground limestone needed to raise the pH of an 18 cm (7 inch) layer of soil by one pH unit from an initial pH of 4.5 or 5.5 ranges from about 2 MT / ha (0.5 short ton / acre) for sandy soil to about 8 MT / ha (2 short tons / acre) for a clay loam. Usually, only the surface becomes acidic enough to require liming.

Sodic soils can be corrected by the application of gypsum. Application rate can be determined by a lab analysis. After the gypsum is applied, the displaced sodium must be leached below the root zone. Organic materials such as manure, cover crop or crop residues may help improve the soil structure for leaching. In established orchards, heavy irrigation during the dormant period minimizes the damage to tree roots from lack of aeration.

 

There is a close association between the composition and concentration of soil salts and salts in irrigation water. When used for irrigation, water with high sodium relative to calcium and magnesium is likely to result in a sodic soil, and therefore needs to be treated before use, or it may jeopardize the long-term wellbeing of the orchard.

 

Source: https://www.oliveoilsource.com/page/fertilizers-and-amendments

 

As mentioned above (Chapter 3, "The mineral nutrition of olive trees"), alkali soils may be acidified to the norm required by olive trees by the application of elemental sulfur. Sulfur in the form of sulfate is not an acidifying material.

It is advisable to acidify the soil gradually, over several years. Two small applications of acidifying material a year apart are better than a single, large application. Soil acidification reactions may take a year or more to complete, so check soil pH annually to monitor the change. Check pH at the same time each year, as soil pH varies seasonally.

 

Acidification before planting

The most effective approach is to add elemental sulfur over a period of years, monitor soil pH and wait until the desired pH is reached before planting. Add elemental S according to the clay content of soil. Mix the sulfur into the soil. Examples for application rate:

 

Acidification of the soil of an existing orchard

Dig a minimum of 4 holes per tree, (preferably 8 – 12), at least 30 cm deep, and 10 – 20 cm in diameter, near the drip line. Mix ~60 g elemental S with the soil removed from each hole. Refill the holes with the soil and water sparingly. Keep the soil around the plant moist, but not wet. This procedure can be performed at any time of the year, but fall is best.

 

The fertilization practices in traditional, extensively-cultivated olive orchards are based mainly on tradition, repeating the same fertilization program every year, enriched by neighbors' testimonials. This practice leads to arbitrary application of excessive rates of some fertilizers, mainly N and, at the same time, to a lack of other nutrients that could be necessary at this growing stage. Also, the excessive application of non-required fertilizers may cause environmental degradation and negatively affect productivity and olive oil quality.

 

From a modern, rational point of view, any amount of a nutrient must be supplied only when there are solid proofs, such as visual and laboratory test results, showing that it’s really needed. For this purpose, leaf-nutrient analysis provides an indication of tree nutritional status, featuring an important tool for determining fertilization requirements.

Fertilization rate can be estimated by the amount of nutrients taken up by the trees and removed from the soil by fruits and pruned branches that are taken away from the plot and by tree mass growth where, although the tree remains in the plot, its nutrients are not available for further growth. All these nutrients need to be returned to the soil in order to retain its fertility for further growth and fruit production.

 

4.2.1 Nutrient uptake / removal

Table 4.1: Nutrient demand / uptake / removal in main olive producing countries

Source: World Fertilizer Use Manual, IFA, 1992

 

 

Source: Kinoch: RSA.

 

Figure 4.1: Uptake of plant nutrients by different parts of olive tree

 

Table 4.3: Nutrients taken up by the plant and removed by crop (5 ton / ha)

Source: Haifa Chemicals website – NutriNet™

As is clear from Figure 4.1, potassium is taken up by all tree organs, including wooden parts, leaves and fruits, in a larger amount than any other plant nutrient.

But, when calculating the needed fertilization, only the amount of plant nutrients removed from the field should be taken into account, such as fruits and pruned branches. These nutrients need to be returned to the soil in form of fertilizers in order to maintain its fertility and so that it should not be continuously exploited.

Some researchers recommend, as a rule of thumb, an annual application of fertilizers equivalent to 2 – 3 fold the amount removed by the harvested crop.

 

4.2.2 Soil and leaf analysis

As explained at the beginning of chapter 3, soil analysis can serve in a very limited way to assess soil fertility for olive trees, while leaf analysis is the preferred method for this purpose. Table 3.1 in chapter 3 details the deficiency, sufficiency and toxicity values of all mineral elements required for olive production.

 

Nitrogen (N), phosphorus (P), potassium (K) and boron (B) are generally the most critical nutrients in the mineral nutrition of olive orchards. Concentration of any of these nutrients can be correctly detected through leaf analysis, which is the best diagnostic method to determine the nutrient status and to plan fertilizer applications.

 

 

Table 4.4: Recommended nitrogen application rate for young olive trees

* The above-mentioned application rates should be used as a guideline that should be corrected according to annual leaf analyses, considering the dynamic trends of the values as well as the absolute values.

** If the trees are bearing at this stage, use the values given below for bearing trees.

Source: Producing Table Olives, by Stan Kailis, David Harris, 2007

 

Bearing orchards

In traditional, extensively grown and rain-fed orchards, nitrogen is usually applied to the soil at0.5 – 1.5 kg / tree, once a year, towards the end of the winter, using urea, ammonium sulfate, or ammonium nitrate; and augmented by foliar spray in the spring, using urea solution at 4%. Other nutrients are applied on an inconsistent basis.

 

In intensively cultivated orchards, phosphorus, potassium and boron, as well as other secondary- and micro-nutrients are applied simultaneously throughout the year. Where Nutrigation (fertigation) systems are available, the use of fully soluble nitrogen fertilizers is very common and the following fertilizers are in wide use:

 

As mentioned, in bearing orchards the basic demand for N-P-K is supplied by application of these nutrients as shown in Table 4.5. To this, traditional growers add, whenever available, organic manures at a rate of 50 kg / tree every 2 – 3 years, applied at the foot of the tree. In this way, they add all nutrients and improve soil structure and infiltration capacity.

 

Table 4.5: Application of basic essential nutrients for olive tree maintenance

As seen in Table 4.2, potassium removal by the fruit is somewhat higher than that of nitrogen, which commands an appropriate compensation by fertilization.

 

This compensation concept is becoming common in many major olive producing Mediterranean countries, such as Spain (Jaen), Morocco and Tunisia (Sfax). But a further step needs to be taken in order to fully implement this concept, namely, the higher the fruit yield removed from the field, and the higher the expected yield for next year, the higher should be the application rate of these nutrients as well as all others that were not included in the basic table above (Table 4.5). For a comprehensive list of these nutrients and their application rates please read Haifa's recommendations in the next chapter.

 

As shown above, traditionally cultivated olives that are not equipped with an irrigation system, usually yield an inferior amount of fruit The application rate of nitrogen, phosphorus and potassium can therefore be relatively modest, e.g., 100, 30 – 40, 200 kg / ha respectively.

 

This application should be done in the second half of the winter and completed before the end of the rainy season, in order to make sure that the minerals are absorbed in the soil but stay in the active root zone, to be encountered by the tree roots without being leached too deep in the soil.

 

The following N and K application plan is based, therefore, on fully-soluble fertilizers, e.g., urea(46-0-0) and potassium nitrate (13-0-46), e.g., Multi-K®. The P should be applied only if indicated by leaf analysis of the previous summer, by broadcasting of a commodity fertilizer such as SSP (single superphosphate) 0-20-0 in late fall. All fertilizers should be applied only under the leaf canopy of the trees.

 

Table 4.6: N-P-K application rates and forms for rain-fed, bearing orchards at yields up to 10 ton / ha (25 kg / tree).

 

An important factor affecting yield is tree density that has many variations in the form of High-Density planting, as well as Super-High Density planting. Clearly, plant nutrient removal is directly affected and thus is presented in the following table:

 

Table 4.7: The effect of planting density on the yield and on plant nutrient requirements

 

A detailed program translating these values to specific fully-soluble products can be found in Table 5.7 in the next chapter.

 

Should the orchard have an irrigation, but not a fertigation system, it is generally more fruitful and therefore needs higher amounts of fertilizers to compensate for the nutrients exported from the soil. The progressive nutrient application rates should then be followed as specified in Table 4.8.

These nutrients should be applied by broadcasting under the trees canopy.

 

Table 4.8: N-P-K application rates and forms, for irrigated, but not fertigated bearing orchards with yields from 6 ton / ha to over 20 ton / ha.

 

* If manure is added, rates should be reduced proportionally to the mineral content of the manure.

A detailed program translating these values to specific fully-soluble products can be found in Table 5.4 in the next chapter.

 

Should the orchard have an irrigation and a nutrigation (fertigation) system, it is generally even more fruitful and therefore needs higher amounts of fertilizer to compensate for the nutrients exported from the soil. The progressive nutrient application rate should then be followed as specified in Table 4.9.

 

Naturally, the nutrigation system allows for a fully flexible nutrient application program that can be easily changed, based on leaf and soil analyses, tree morphology, pest situation, climatic and irrigation-water conditions, market opportunities and threats regarding fruit prices as well as fertilizer prices. The full flexibility of the nutrigation system enables fertilizer application even in the winter months, when a rain-fed orchard is generally not fertilized. It goes without saying that the nutrients are applied by the water emitters of the orchard.

 

The following application program is a real case that represents the considerations taken while planning a fertigation program in a Mediterranean-type cultivation region. The program is detailed by application months.

 

Intended use: Oil extraction

Trees density: 500 trees / ha

Soil type: Light to medium

Expected yield: 30 MT / ha

 

As can be seen, the fertilizer rates are indicated per month, and the grower is able to further divide the monthly rates into weekly amounts. Clearly, the rates recommended need to be adjusted according to leaf analysis results.

 

Table 4.9: Fertigation schedule under Mediterranean growing conditions

A detailed program translating these values to specific fully-soluble products can be found in Table 5.6 in the next chapter.

 

Foliar spraying and feeding is a unique application method, helpful in satisfying plant requirements promptly and with high efficiency. Nitrogen and potassium are easily absorbed in the plant and distributed into the plant when applied to the leaves. Foliar feeding is a useful solution, especially for rain-fed orchards in arid zones where the scarcity of water in the summer drastically reduces nutrient absorption from the soil, hence making it difficult to correct deficiencies, exactly when the trees may also lose a great deal of their productivity due to drought conditions.

 

Additionally, foliar fertilizer applications are also important under normal growth conditions, by supplementing nutrient requirements at peak demand periods. Olive nutrition is of critical importance in the spring (when flowering and vegetative growth take place), and at the end of the summer, before harvesting. Foliar applications help accelerate vegetative growth and reproductive development, encouraging shoot growth, improving fruit-set and reducing alternate bearing.

Therefore, if foliar feeding is the only source for application during peak demand, several applications should be carried out.

The olive fruit is very efficient at removing nutrients from the leaves. Foliar sprays help enrich the leaves at these high nutrient demand periods. Foliar sprays during this period will help increase yield and improve the nutritional quality of the oil.

The following part of this chapter will supply a lot of scientific information describing the achievements of foliar feeding in olives in different parts of the world.

 

A field trial was conducted in Israel on the Barnea cultivar, which was treated with 4 foliar applications of Poly-Olive™ 15-7-30+2MgO enriched by micro nutrients including 4,500 ppm boron at 2%. (For product details see the special paragraph in chapter 5 after Table 5.9.) This resulted in larger fruit size and better ripening (Figure 4.2).

 

Figure 4.2: Effect of Poly-Olive™ 15-7-30+2MgO with micro nutrients on fruit ripening

 

A field trial was conducted in Israel, on the Barnea cultivar, when the trees were 8 years old, under intensive cultivation. Tree spacing was 3 x 7 m; average yield in the three years prior to the trial was 15 T / ha / year. Despite massive soil fertilization, deficiencies of macro- and micro-nutrients were apparent. Trees were treated with Poly-Olive™ 15-7-30+2MgO+ME, at 2% or 4%.

 

To study the effect of application timing, foliar nutrition was applied at three different phenological stages: at inflorescence, after fruit-set and after stone hardening.

 

Figure 4.3: The effects of foliar application of 2% Poly-Olive™ on fruit-set and fruit yield as measured in the second year of the trial

 

In Tunisia, (Sfax region) potassium requirement of rain-fed Chemlali trees was estimated based on a yield of 200 kg / tree. Two rates of potassium nitrate (Multi-K) were applied by foliar spray as follows:

The foliar feeding of each treatment was distributed to three applications as follows:

 

Results: Leaf area, leaf mineral content and fruit indices at harvest

The leaves of the two foliar treatments had a higher leaf area than the control (Figure 4.4). Moreover, these leaves were also richer in the minerals applied, i.e., N and K, and did not change the contents of other minerals; data not shown (Figure 4.5).

 

These increases have enhanced leaf photosynthetic capacity, having a remarkably positive effect on fruit development and value (Figure 4.6).

 

Figure 4.4: The effect of different rates of potassium sprays on olive leaf areas

Statistics analysis by Duncan's test

 

Figure 4.5: The effect of different rates of potassium nitrate sprays on leaf mineral composition compared to Freeman et al. (1994) norms

Statistics analysis by Duncan's test

 

Figure 4.6: The effect of different rates of potassium nitrate sprays on the pomological characteristics of olive fruits

Statistics analysis by Duncan's test.

 

Figure 4.6 shows that flesh / pit ratio and fruit weight were highest in the Multi-K F100 treatment, statistically significantly lower in the Multi-K F50 treatment and, again, statistically significantly lower in the control treatment. Fruit growth was more intensive during stage 3 for the Multi-K F100 treatment (data not shown).

 

Conclusions

 

Turkey

Foliar application of potassium nitrate is a well-known and recommended procedure in olive orchards in Turkey, due to low potassium contents in many local soils. In a study carried out by Dikmelik, Puskulku & Altug of the Olive Research Institute at Ege University, Turkey, in 1998, with the important cultivar "Memecik", four foliar sprays were done at 4%. Two foliar feeding treatments (20 days apart) were done after fruit-set (May); two additional sprays (20 days apart) were done after pit hardening (August). The sprays were done as 4% potassium nitrate at 1,000 L / ha, sometimes combined with urea. These foliar treatments were compared with the local commercial habit of the growers of side dressing with potassium-sulfate (SOP).

 

Table 4.10: Comparison between soil application of SOP, and foliar feeding of potassium nitrate

 

Conclusions

Foliar applications of Multi-K, carried out from the first rapid growth period of fruit (summer) till maturity (end of early fall), were found to have highly positive effects on the nutrition status of the trees that suffered from insufficient potassium. The quality of the treated table olives was highly improved due to increase in size, higher pulp / pit ratio and higher oil content.

 

Crete

The effect of the eight factorial combinations of summer soil and spray application of two levels of N and two levels of K on the mineral composition of olive leaves was studied in an irrigated olive orchard (cv. Manzanillo) in Crete.

Potassium nitrate in the form of Multi-K was sprayed at 4% four times during July and August.

N and P contents of the leaves were increased by potassium nitrate spray applications. The applications of urea, shortly before the potassium nitrate sprays, significantly enhanced the uptake of K in the leaves.

 

 

Need more information about growing olives? You can always return to the olive fertilizer & olive crop guide table of contents

 

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