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HELLENIC AGRICULTURAL

ORGANIZATION “DEMETER”

Fertilizing Olive Trees

Dr Georgios Psarras

Institute for Olive Tree & Subtropical Plants

Lab of Plant Mineral Nutrition & Physiology

Introduction

Law of Minimum(von Liebig)

Max yield

Potential

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Introduction

DEFICIENCY ADEQUACY TOXICITY

Nutrient concentration

In leaves

Pla

nt

Gro

wth

MacronutrientsNitrogen (Ν)

Phosphorus (Ρ)

Potassium (Κ)

Calcium (Ca)

Magnesium (Mg)

Sulphur (S)

Iron (Fe)

Manganese (Mn)

Zinc (Zn)

Boron (Β)

Copper (Cu)

Molybdenum (Μο)

Chloride (Cl)

Micronutrients

Plant Nutrient Requirements

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Sustainable fertilizing schedule

A sustainable fertilizing schedule has to: Retain nutrient concentration within adequacy

range Avoid deficiencies

Avoid toxicity

Retain nutrient balance

Replace nutrient removal from the orchard (removal from yield, pruning, etc.) Use of chemical fertilizers

Use of organic fertilizers or other organic material

Recycling of material removed from the tree (prunings, olive oil by-products, etc.)

Sustainable fertilizing schedule

Appropriate application scheduling:

Reduce fertilizer losses

Apply nutrients during the high nutrient demand season

Protection of the environment

Improve soil fertility

Increase of organic matter

Maintain pH within the appropriate limits for olive

Improve soil texture

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Defining nutrient requirements

Defining nutrient requirements is a key issue

for a sustainable fertilizing schedule

There are some basic estimates of nutrient

removal, mostly based on tree yield that will be

presented later on

However, these estimates may vary

considerably and data for local conditions

and/or cultivars should be available, since

olive tree is cultivated under significantly

variable orchard management schemes

“Natural” vs intensive management

Several of the traditional orchards are typically

adopting “low-input” management scheme,

resulting to a “low-output” (yield) too.

The potential for converting this “low-input”

system into a more productive but also more

intensive scheme, greatly depends on the

existing abilities to overcome current

restrictions.

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Olive tree growing systems

Growing system % world-wide Density (trees/ha)

Traditional in marginal

areas

20 Up to 100

Traditional – able to be

mechanized

50 Up to 100

Intensive 29 Up to 400

Hedgerow 1 1200 - 2000

Source: Tous et al., 2011

Empirical vs sustainable

In several cases, the existing pool of nutrients in the

soil is considerably higher than actual nutrient removal

and therefore, especially in traditional olive orchards,

the need for fertilizer use is limited for most of the

essential mineral nutrients

Since the actual nutrient requirements cannot easily

be calculated, even by agronomists, for a specific

orchard, it is obvious that empirical application of

fertilizers by farmers may lead to serious mistakes that

may increase the production cost and definitely reduce

the efficient use of resources

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Important knowledge and tools

Knowing the nutritional status of the tree:

Leaf analysis

Knowing key soil properties and indicative nutrient

availability:

Soil analysis

Olive tree fertilizing

The nutrients that are most commonly used for olive

tree fertilizing are N, P, K and B

In several cases and depending on local soil

properties, Ca and Mg might also be used, as well as

the rest of mineral elements in case of proven

deficiency

For every 50 kg of olive fruit produced, the amount of

nutrients that are removed are: 450 g N, 100 g P, 500

g K and 200 g Ca

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Olive tree nutrient removal by

yield and pruning

According to Fernandez-Escobar et al., 2015:

N

kg/Ha

P

kg/Ha

K

kg/Ha

Ca

kg/Ha

Amount 54.4 6.87 45.5 57.9

Main Source Yield and

Pruning

Yield Pruning

Introduction

Annual requirements for mineral elements vary considerably among different orchards depending upon: Tree age

Planting density

Cultivar

Pruning

Rainfall and availability of irrigation water

Soil characteristics: Soil texture

Soil carbonate content

Soil organic matter

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27%

73%

IRRIGATED

Low

Normal58%

42%

RAINFED

Low

Normal

Nitrogen

41%

59%

IRRIGATED

Low

Normal 65%

35%

RAINFED

Low

Normal

Potassium

Nitrogen

Typically, in fertilized orchards, N is added on an

annual basis

Typical Mediterranean soils are low in organic matter

and therefore:

Plants use almost exclusively the N added through fertilizers

It is important to replenish soil N resources

Olive tree responds to N fertilizing in various ways

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Nitrogen

Increased yield

Higher flowering quality

Longer shoot growth

Reduced biennial bearing fluctuations

Nitrogen cycle in the farm

Ν2

Atmospheric Ν

Mineral N

Fertilizing

Organic Ν

(Manure,

Compost, etc)

NH3

Ammonia

Soil

Organic N

ΝΗ4+

Αμμωνιακό Ν

Mineralization

ΝΟ2-

ΝΟ3-

Nitrate-N

Nitrification

Leaching

N fixation

Uptake by

Olive trees

N-fixing

plants

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Nitrogen

N losses depend upon climatic conditions (rainfall events), soil type and orchard topography (slope)

NO3-N leaching High rainfall

Coarse soil texure, Low organic matter

Atmospheric losses Hot and dry environment

High soil CaCO3 content (calcareous soil)

Flooded soil (anaerobic conditions)

Surface runoff losses Orchards on high slopes and increased soil erosion risk

High rainfall rates after application

Nitrogen

Long-term experiments in Crete showed that addition of 0,8 kg

N/tree can increase yield by 52-105% as compared to non-

fertilized control trees.

N fertilizing increases:

the number of perfect flowers

The length of annual shoot growth

The number of nods per shoot

The number of inflorescence

No effects on fruit drop percentage and total number of flowers

per inflorescence

Shoot growth starts earlier, an advantage for rainfed orchards.

Flowering and fruit set are also completed earlier.

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Nirogen

Low N content short length of annual growth and pale leaf color (chlorosis in whole leaf surface)

High N content long annual shoot growth, low yield, dark green leaf color

Long annual shoot growth no flower differentiation

Very short annual growth low yield potential for next year

Therefore, a balanced N fertilizing is required for achieving a good yield

Nitrogen deficiency

Source: Production Techniques in Olive Growing. IOC, 2007.

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Nitrogen

Typical annual requirements of olive trees range from

0.5-1.0 kg Ν per tree (not exceeding 150 kg/ha)

depending mostly on:

Tree size

Planting density

Water availability

If reduced water availability severely inhibits plant growth

and yield, then total N uptake (and fertilizing need) is also

significantly lower

In rainfed orchards, high N application rates may reduce

uptake of other nutrients, like K

Nitrogen and fruit/oil quality

Experiment: cv. ‘Picual’ in 2 areas with N applied either 100% from soil or 50-50 (soil-foliar appl.), after 3 years:

Total phenolic content was reduced as N content was increased reduced oil tolerance to oxidation and reduced bitterness.

Tocopherols were increased as N content was increased.

No effect on carotenoids, chlorophyll, and fatty acid composition.

Source: Fernández-Escobar et al., 2006

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Nitrogen and olive oil quality

Higher doses of N and P:

Decreased polyphenol content

Decreased peroxide value

Decreased MUFA C18:1

Increased PUFA C18:3

K dosage did not affect oil quality parameters

Source: Dag et al., 2009

Phosphorus

Under field conditions, olive tree yield is not affected

by P application in most cases.

However, low P content has been recorded in areas

cultivated for the first time (new orchards) and in acidic

soils in Crete.

Use of composite fertilizers usually leads to P surplus

in leaves and high levels of P in the soil.

Nonetheless, P is a quite important element for olive

tree, as in any other plant, and we have to be sure that

trees have adequate P levels.

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P and fruit yield

Source: Erel et al., 2008

Phosphorus and olive oil quality

Higher doses of N and P:

Decreased polyphenol content

Decreased peroxide value

Decreased MUFA C18:1

Increased PUFA C18:3

K dosage did not affect oil quality parameters

Source: Dag et al., 2009

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Phosphorus

Phosphorus in the soil

Phosphorus is strongly bound in the soil and only a

small part is available to the tree

P movement in the soil is very slow (in contrast to

N).

The highest risk for P losses is related to soil

erosion in sensitive areas

Phosphorus

Visual symptoms of P deficiency in the field is quite

rare.

Therefore, leaf analysis is usually the only way to

detect P deficiency

When P leaf content is marginal or low, winter

application of P usually solves the problem. Typical

rates for medium-sized trees are 0.4-0.6 kg P2O5/tree

However, the exact rate of application should be

defined taking into account various soil properties

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Potassium

Potassium deficiency is quite common in olive

orchards

K deficiency is more common in rainfed orchards,

where high K requirements coincide with the peak of

the dry season

Typical symptoms: chlorosis developing to necrosis of

leaf tip and/or leaf edges.

In severe cases: leaf drop and shoot necrosis. In such

cases severe impact on yield.

Source: Production Techniques in Olive Growing. IOC, 2007.

K deficiency symptoms in leaves,

shoots and fruit

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Potassium

A typical dose for trees with a mean annual yield of 50 kg of olives is 0.5 kg K2O/ tree

This is the maintenance dose when soil and leaf content are within the adequacy range.

When there is a strong biennial bearing cycle, then K is preferably applied when the high yield is expected (“on” year).

In cases where soil K content is significantly low, then the application rate may be double or triple than actual tree requirements, depending on soil type, in order to restore K availability in the soil.

Calcium

Ca deficiency is not quite common, since olive is

traditionally cultivated in calcareous soils.

Typical symptom is leaf tip chlorosis

In table olives, Ca has been related (together with B)

to fruit abnormalities (soft nose)

Use of fertilizers than can lower soil pH may enhance

the Ca deficiency problems

Significant Ca deficiency problems have been

observed in soils with high Mg content

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Ca deficiency symptoms in

olive leaves

Calcium

Low Ca levels are typically linked to soils with

low CaCO3 content and low pH.

In such soils, soil liming is recommended

anyway, in order to improve soil pH. This

practice usually improves Ca uptake and

resolves the problem.

When soil pH is not a limiting factor (i.e. >6.5),

then fertilizers with readily availables forms of

Ca are applied (i.e. calcium nitrate)

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Magnesium

Typical symptoms of deficiency: chlorosis developing

from leaf edges and developing inwards. Symptoms

develop in older leaves.

Not a common deficiency in Greece, due to existing

soil types

However, it is an important macronutrient, which

should be monitored by leaf analysis and be included

in fertilization scheduling if levels in leaf and soil are

low

Magnesium

Source: F. Nigro, 2015

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Magnesium

Similarly to Ca, low soil availability is linked to low soil

pH.

When low Mg levels are detected in a low pH soil, then

liming with dolomite (containing both Ca and Mg)

should be applied.

When soil pH is not a limiting factor (i.e. >6.5), and leaf

analysis shows low Mg levels:

Soil or foliar application of MgSO4 can resolve the problem

(up to 2 kg/tree for soil application, repeated periodically)

Maintenance with Mg-containing fertilizers (e.g. K-Mg

sulphate)

Boron

The most common micro-nutrient deficiency for olive

trees.

Common to many different soil types, like coarse-

textured soils (B lost by leaching), fine-textured soils,

low or high soil pH (reduced B mobility in soils with

high clay, or carbonates or Al, Fe, Mn oxides)

Soil moisture greatly affects B availability

High organic matter in the soil can improve B release

to the nutrient solution

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Boron

Symptoms appear in both young and mature olive

trees, but deficiency develops faster in young trees

Step 1: Leaf tip chlorosis that develops to necrosis.

Leaves might have flattened tips and be smaller in

size

Step 2: Shoot growth is limited and lateral buds

develop instead of shoot-tip buds, resulting in “Witch’s

broom” symptom.

Step 3: Shoot necrosis and leaf drop

Boron

Brown necrotic spots may develop in thicker shoots

Under B deficiency, flowering is limited and fruit-set is

lower than normal.

Fruit drop and deformation of remaining (“monkey

face” symptom) are also typical

Despite the great variety of symptoms in several cases

it can be confused with other nutritional problems

Therefore, leaf analysis is again quite useful in early

detection of B deficiency, before developing severe

symptoms

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B deficiency in leaves

and fruit of cv.

“Throubolia”

Boron

Controlling B deficiency:

When B deficiency is diagnosed, typical treatment

is the application of 100-500 g of Borax per tree

(could be even higher for very large trees) during

winter.

Depending on soil type (especially in calcareous

soils) response to soil application may be delayed

or limited

Alternatively: foliar application of Borax (0,6-0,8 %)

before flowering

Quick response

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Boron

Soil application should be repeated every 3 years

Over-dosing in B application may lead to B toxicity

Use of composite fertilizers containing small

amounts of B could be effective for maintenance,

but may not be adequate for correcting a severe

deficiency

Other micro-nutrients

Deficiencies of zinc and copper are not as

common.

In general, micronutrient deficiencies are

linked to alkaline soil pH

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Zinc

Despite the fact that olive is typically cultivated

in calcareous soils with high pH, where Zn

availability is low, in general, olive tree is not

as sensitive in developing Zn deficiency as

other tree crops (e.g. citrus)

However, in recent years several cases of Zn

deficiency have been detected

Recent work has linked Zn deficiency to high P

levels in soil and olive trees

Copper

Rarely found in low concentrations in leaves

Usually, application of Cu-containing

fungicides also covers (in surplus) the olive

tree requirements

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Iron

Iron deficiency symptoms have been detected in olive

trees grown in calcareous soils with high pH

Flooding conditions in the soil may enhance Fe

deficiency problems

Cultivar seems to be the most important factor in

developing Fe deficiency in calcareous soils

Symptoms: leaf yellowing with veins remaining green,

loss of vigor and reduced yield

Fruit are smaller and pale in color (disadvantage for

table olives)

Iron

Iron deficiency is not easily detected by leaf

analysis.

Therefore, it is the only nutrient deficiency that

is better detected by the visual symptoms in

the trees (linked to soil analysis)

Difficult to correct (high cost)

Therefore, avoid its development is better than

trying to resolve the problem

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Iron

Planting non-sensitive cultivars in calcareous

soils is essential

Using a tolerant cultivar as rootstock could be

another alternative

Reference Sensitive Less sensitive Tolerant

Pastor et al., 2002 Arbequina,

Manzanilla de

Sevilla

Cornicabra,

Hojiblanca,

Nevadillo negro

Alcantara et al.

2003

Leccino, Arbequina,

Lechin de Sevilla,

Galega

Cornezuelo de

Jaen

Nevadillo negro,

Pajarero,

Manzanilla de

Sevilla

Iron

Source: Production Techniques in Olive Growing. IOC, 2007.

Fe deficiency symptoms in

leaves and fruit

Source: Franco Nigro, 2015

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Toxicities

NaCl toxicity

B toxicity

Mn toxicity

In summary

N is typically applied on an annual basis

P is usually in surplus in soil and leaves when compound fertilizers have been used for several years

In highly productive trees, K is also used on an annual basis, due to significant removal by the produced fruit

B has to be periodically applied in most olive orchards

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Defining mineral nutrient requirements

For defining the nutrient requirements and

develop a fertilizing schedule, the agronomist

should have in hand the following information:

Informative material on key orchard characteristics:

Age, density, tree size, water availability, mean annual

yield, visual symptoms of deficiency, fertilizing during the

last 3 years, etc.

Soil analysis, at least for basic soil properties and

macro-nutrient content

Leaf analysis

Soil analysis

Soil analysis:

The knowledge of key soil characteristics is essential for

defining the details of a fertilizing schedule. Important

parameters are:

Soil pH and CaCO3 content

It is important to define the type of fertilizers to be used

In soils with pH>7 and adequate CaCO3 the use of ammonium

sulphate is preferable

In soils with lower pH and low CaCO3 the use of fertilizers that do

not contribute to soil acidification is preferable (e.g. calcium

ammonium nitrate)

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Soil pH effect on nutrient

availability

NK

Ca

P

Fe

Mg

S

Mn

MoZn

Cu

B

Soil analysis

Soil salinity:

Usually, when good quality water is used for irrigation soil

salinity levels are <1 dS/m

Increased salinity is usually linked to the use of saline

irrigation water

When soil salinity is high, the use of fertilizers containing

Cl (e.g. potassium chloride) is avoided since they may

enhance the problem

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Soil analysis

Soil texture

Coarse textured soils (sandy):

Higher losses of nutrient due to leaching

Measures like increase of organic matter, application of fertilizers

at the end of the raining season, splitting of N application in more

doses and fertigation should be considered

Fine-textured soils:

Elements like K are strongly bound and less available to plants.

Higher doses of K, Ca and Mg might be required in order to

correct deficiency problems

Measures to avoid flooding should be taken, since it results in

root damage, stunted growth and nutrient uptake, if it occurs

during spring

Soil analysis

Soil organic matter content

High organic matter % can provide significant amounts of

N, P and micronutrients and therefore, application of

chemical fertilizers should be adjusted accordingly

Increasing of soil organic matter is always favourable in

improving nutrient availability and reducing losses

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Soil analysis

Soil mineral element availability

Much more important for annual crops

However, it provides useful information concerning the

availability of some key macro-nutrients

The complexity of mechanisms involved in soil nutrient

availability and the antagonistic effects among different

nutrients make difficult the prediction of the actual

nutrient availability to the plant. Leaf analysis is far more

important in determining the existing nutritional

problems.

Soil sampling

Timing

Not many restrictions

For practical reasons: when soil is wet and before the

application of fertilizers

Sampling

Ideal: use of auger for extracting a soil profile from 5-30

cm

In deep soil profiles a second sample beyond 30 cm

may be taken, although nutrient uptake is usually taking

place in the upper 30-40 cm

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Soil sampling

Sampling

For small orchards (up to 0.5 ha) and uniform soil, 1

composite sample per depth is collected

When an known or visible soil variability exists, 1

sample for each case is collected, independently from

field size

In large orchards, it is recommended to take more than

1 samples, independently from soil uniformity

Soil sampling

Sampling

Sampling point: under the tree canopy or in the area

where fertilizer is spread.

Tree canopy

Fertilizer

application

area

Right sampling

point

Wrong sampling

pointX

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Soil sampling

Sampling

In irrigated orchards it is better to sample along the drip

line

Drip line

Sampling points:

• At least 10

points per

sample

• After mixing

about 1 kg

is sent for

analysis

Soil sampling

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Soil analysis interpretation

Parameter Values

Soil pH 6.5 – 8.0

Soil texture Medium-textured

Total CaCO3 >2%

Organic matter content >2%

Electr. conductivity <4 dS/m

NO3-N 10-20 mg/kg

P 10-20 mg/kg

K (medium soil texture) ~150 mg/kg

Ca (medium soil texture) >1000 mg/kg

Mg (medium soil texture) ~100 mg/kg

Fe >3 mg/kg

Zn >0.8 mg/kg

Mn >1.4 mg/kg

Cu > 0,2 mg/kg

B >1 mg/kg

Defining mineral nutrient requirements

Leaf analysis

Defining the mineral nutrient content in leaf tissue is

the most important tool to detect nutritional

deficiencies, imbalances and toxicities in an olive

orchard

Using this information, and knowing key soil

properties and basic information about the orchard

we try to interpret the analysis and detect the

source of the problem

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Defining mineral nutrient requirements

Sample recording information (Ref.

No., Farmer, Location, Contact

Information, etc.)

Crop and cultivar

Tree age

Planting density

Tree size

Visual deficiency symptoms

Other important problems

Winter fertilizing schedule (last 3

years)

Foliar applications or fertigation

Irrigated or rainfed

Defining mineral nutrient requirements

Leaf analysis

Detecting the source of nutritional problems

Low nutrient availability in soil adding the missing

nutrient

Antagonism minimize application of another nutrient

Wrong application timing optimize timing rather than

increase amount

Wrong application method adjust (e.g. foliar application

instead of soil application)

Low uptake due to soil pH adjust (e.g. liming)

Disease Disease control

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Defining mineral nutrient requirements

Leaf analysis

Based on the above, we give information for

required modifications, additions or exclusions to

the existing fertilizing scheduling

Leaf analysis

Orchard information

Previous fertilizing schedule

Leaf analysis

Adjusting

Fertilizing

Soil analysisSelect fertilizer

type, frequency or

method

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Leaf analysis

Orchard information

Previous fertilizing schedule

Leaf analysis

Adjusting

Fertilizing

Soil analysisSelect fertilizer

type, frequency or

method

Ν P K Ca Mg Fe Zn Mn Cu

Ε

Φ

Ε

Φ

Ε

Φ

Ε

Φ

Ε

Φ

Ε

Φ

Ε

Φ

Δείγμα 1

Δείγμα 2

Δείγμα 3

Δείγμα 4

Δείγμα 5

Δείγμα 6

Δείγμα 7

Very Low

Low

Optimum

High

Excess

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Leaf analysis

Sampling time:

In all tree crops, leaf nutrient content is changing

over time depending on leaf age and plant growth

cycle.

Therefore, leaf analysis is performed during a

period where the content of different elements is

the most stable.

Moreover, the standards that have been developed

also refer to a certain period and not to the whole

growing season.

Leaf analysis

Two possible periods:

Summer: Second half of July

Winter: Late October - November

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Leaf analysis

Period of sampling

Summer sampling:

+ The leaf content is not affected by the fruit load

+ Fertilizing can be adjusted according to the

known expected fruit load

- Rainfed trees might already be stressed and

therefore nutrient content be affected by water

stress and not by nutrient availability

- Not enough ways to correct nutrient deficiencies

at that period of time in most of the orchards

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Period of sampling

Winter sampling:

+ The tree water status is adequate

+ The degree of exhaustion is known and

measures can be taken in order to avoid key

nutrient deficiencies early in the following season

- Nutrient content might have been affected more

by fruit yield than by nutrient availability in the soil

Leaf sampling

Leaf age:

Leaves from current growth

3-5 months old

Sample size:

About 200 leaves

At least 10-20 trees. Trees should be

representative of the typical situation for the

orchard.

Selected shoots also representative.

Avoid leaves or trees with disease damage or

any other distinct symptom and trees at the

borders of the orchard

Sample taken at human height (middle

section of the canopy)

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Leaf sampling

Number of samples:

1 sample for each uniform block of soil

Different samples if trees of different age, cultivar, management

system, etc. are present

Sample treatment:

Ideally: place in a cool box and transfer to the lab

If leaves are not to be transferred soon to the lab, they have to be

stored in the refrigerator for short period (1-2 days).

Soil and leaf analysis time-frame

1. A soil analysis detects key soil properties and

nutrient availability

2. Leaf analysis detects nutritional problems.

3. Leaf analysis is repeated for 1 or 2 years to

finalize adjustments.

4. After that, leaf analysis is repeated every 2-3

years

5. Soil analysis is repeated every 5 years

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Proposed values for leaf analysis interpretation (October-November sampling / leaves

5-6 months old).

ElementDeficiency Low High Excess

Nitrogen (%) <1.2 1.2-1.6 1.8-2.2 >2.2

Phosphorus (%) <0.07 0.07-0.10 0.13-0.15 >0.15

Potassium (%) <0.5 0.5-0.8 1.1-1.3 >1.3

Calcium (%) <0.5 0.5-1.0 >2.5

Magnesium (%) <0.07 0.07-0.10 >0.30

Boron (ppm) <15 15-20 50-150 >150

Iron (ppm) 20-50 150-500

Zinc (ppm) 5-10 >30

Manganese (ppm) <10 10-20 60-150 >150

Copper (ppm) <5 >20

Source: Androulakis I.

Proposed values for leaf analysis interpretation (July sampling / leaves 3-5 months old).

ElementDeficient Toxic

Nitrogen (%) 1.4 --

Phosphorus (%) 0.05 --

Potassium (%) 0.4 --

Calcium (%) 0.3

Magnesium (%) 0.08

Boron (ppm) 14 185

Iron (ppm)

Zinc (ppm)

Manganese (ppm)

Copper (ppm)

Source: Fernandez-Escobar 2004

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Fertilizing olive trees

As soon as the nutritional status of the tree and the soil properties

are known, a fertilizing scheduling is issued, determining:

The timing of application

The type of fertilizer to be used

The quantity of fertilizers (depending upon the nutrient contant of the

selected type)

Additional corrective measures to be taken to improve soil fertility, or

other properties

The optimal application method to be used depending on available

means and soil properties

Alternative methods to be used

Soil application (winter or spring)

Fertigation

Foliar application

Injection

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Soil application - Timing

Optimal timing depends upon the climatic conditions of the area

Water is a crucial factor (amount and distribution of precipitation)

Κ, Ρ, Β: Up to the end of December (Cretan example)

Ν fertilizers (Cretan example):

Ammonium sulphate: Second half of January

Calcium ammonium nitrate: mid-February

Ammonium nitrate: Before the last rainfalls

Application of ammonium-containing fertilizers should not be followed by extended periods of hot and dry weather

Soil application – Type of fertilizer

In general, it is better to select single-element fertilizers, as compared to compound fertilizers Timing of N vs P or K application is different and therefore

optimal timing cannot be achieved by the use of a composite fertilizer

Depending on soil pH, different fertilizers have to be used: Alkaline pH and high CaCO3 Ammonium sulfate

Acid pH and low CaCO3 Calcium ammonium nitrate

Salinity and soil texture issues should be considered: Avoid Cl containing fertilizers in soils with high salinity (e.g.

KCl)

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Fertilizer labeling example

18-6-12

18% N

6% P2O5

12% K2O

Content of additional

nutrients is also

mentioned

Terminology:

Fertilizing Unit

Examples of single-nutrient

fertilizers

Nitrogen

Ammonium sulfate (21-0-0)

Calcium ammonium nitrate (26-0-0)

Ammonium nitrate (34-0-0)

Urea (46-0-0)

Potassium

Potassium sulfate (0-0-50)

Potassium chloride (0-0-60)

K-Mg sulphate (0-0-30)

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Soil application

Mechanical

Soil application

Manual

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Soil application

Incorporation to the soil is in general

suggested at least for K and P fertilizers

However, especially in sloppy areas, the

disadvantages of any kind of soil cultivation

are more than the advantages of fertilizer

incorporation

Soil application during spring

In areas where there are significant rainfall

events during spring, application of N fertilizers

could be split in 2 (winter + spring application)

Advantages:

Lower risk of losses through leaching

Nitrogen demand during spring is high

Ammonium nitrate is the typical fertilizer used

Not applicable in areas where spring is

typically “dry”

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Fertigation and foliar application

Apart from application of fertilizers to the soil,

foliar application and fertigation are also

practiced in olive orchards

Both methods have the advantage of targeted

application timing that coincides with high

demand periods for certain nutrients

However, cost of application and lack of

means of application lead to limited use in

most traditional olive orchards

JAN FEB MAR APR MAY JUN AUGJUL OCT NOV DECSEP

Dormancy Active shoot

growth

Limited shoot

growth

Active shoot

growth

Dormancy

Flower. bud

differentiation

Fruit

growth

Increase of

Oil contentFruit-

set

Pit

hardening

Flower bud

formation

Flowering

Fruit color

change

Maturation

Harvesting Harvesting

Annual growth cycle – Mineral nutrient requirements

High demand on nutrient requirements

B N K

Determination of yield potential

JAN FEB MAR APR MAY JUN AUGJUL OCT NOV DECSEP

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49

Fertigation

Advantages:

Fertilizer is applied in the root zone under favorable soil moisture

conditions and therefore nutrient uptake ratio is higher as compared

to soil application during winter

The nutrient use efficiency is increased

Nutrient losses are limited

Application can be adjusted according to expected fruit load

Disadvantages:

Only applicable in irrigated orchards

Only applicable under certain irrigation methods

Not adequate experimental data exist for most areas and cultivars

In problematic soils it may increase soil salinity problems

Costs involved

Problems in scheduling in areas where water availability is limited

Fertigation

It can be applied as an exclusive method for

nutrient application, or additionally to winter

application

Data from a summer foliar analysis program

could be used in an optimal way at fertigated

olive orchards

At a higher cost, the application of water and

nutrients could be fully automated

Application of water and nutrients at high rates

could reduce olive oil quality

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50

Fertigation

Nitrogen: If fertigation is exclusively used for fertilizing the

orchard, applications should start early in spring, even if there is

no need for irrigation

Potassium: Higher demands after June

Fertigation

Not all fertilizers are equally appropriate to be

used for fertigation

FertilizerN – P2O5 – K2O

content

Solubility

(g/l) at 20 C

Ammonium nitrate

Ammonium sulphate

Urea

Monoammonium phosphate

Diammonium phosphate

Potassium chloride

Potassium nitrate

Potassium sulphate

Monopotassium phosphate

Phosphoric acid

34-0-0

21-0-0

46-0-0

12-61-0

18-46-0

0-0-60

13-0-44

0-0-50

0-52-34

0-52-0

1830

760

1100

282

575

347

316

110

230

457

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Foliar application

Advantages: When soil properties do not favor the uptake of certain

nutrients, foliar application can be the most effective way to correct deficiencies

Tree response is faster, as compared to soil application

An alternative for rainfed orchards in cases of long dry periods that do not favor soil application

Foliar application

Disadvantages: Application rates are low and therefore macronutrient

requirements (N or K) cannot be covered by a single foliar application. Usually applied as a supplementary method

Cost may be high to cover macronutrient requirements

Not effective for long. It usually covers the annual requirements of micronutrients but should be repeated on an annual basis

Rainfall after application may affect the effectiveness

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Foliar application

Efficiency of foliar application is affected by

several environmental factors:

Light, Temperature, Humidity

Effects of environmental factors could be:

Direct effects on spray solution prior to absorption

Indirect effects on leaf development processes

Indirect effects on photosynthesis, stomatal

opening and sink activity, affecting energy and

metabolite availability involved in the uptake

process

Foliar application

Nutrient uptake is higher in young olive leaves as compared to older leaves

Not well hydrated leaves (water stressed) uptake less nutrients than fully hydrated leaves.

Therefore, spring (preferably) and autumn (if rain occurs) sprays are more effective than summer sprays

Avoidance of hot days and application during the cooler part of the day increases absorption

Surfactants are used to increase absorption

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Foliar application

Foliar application has been effectively used as a supplementary method for applying N or K in olive trees

In cases of severe K deficiency trees may respond faster as compared to soil application

There are reports suggesting that late spring application of K gave better results than late summer application in olive trees

Not effective for Fe application

Spring application of Boron may enhance fruit set as compared to untreated olive trees

Common compounds used

Macronutrient Common element

compounds

References

N Urea, ammonium sulphate,

ammonium nitrate

Zhang et al. (2009); Fageria et

al. (2009)

P H3PO4, KH2PO4, NH4H2PO4,

Ca(H2PO4)2, phosphites

Noack et al. (2011); Schreiner

(2010); Hossain and Ryu (2009)

K K2SO4, KCl, KNO3, K2CO3,

KH2PO4

Lester et al. (2010), Restrepo-

Dνaz et al. (2008)

Mg MgSO4, MgCl2, Mg(NO3)2 Dordas (2009a), Allen (1960)

Ca CaCl2, Ca-propionate, Ca-

acetate

Val and Fernαndez (2011);

Wojcik et al. (2010); Kraemer et

al. (2009a,b)

Source: V. Fernandez, T. Sotiropoulos. P. Brown, 2013

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54

Common compounds used

Micronutrient Common element

compounds

References

B Boric acid (B(OH)3), Borax

(Na2B4O7), Na-octoborate

(Na2B8O13), B-polyols

Will et al. (2011); Sarkar et al.

(2007), Nyomora et al. (1999)

Fe FeSO4, Fe(III)-chelates, Fe-

complexes (lignosulphonates,

glucoheptonates, etc.)

Rodriguez-Lucena et al.

(2010a, 2000b); Fernαndez et

al. (2008b); Fernαndez and

Ebert (2005); Moran (2004)

Mn MnSO4, Mn(II)-chelates Moosavi and Ronaghi (2010),

Dordas (2009a), Papadakis et

al. (2007), Moran (2004)

Zn ZnSO4, Zn(II)-chelates, ZnO,

Zn-organic ‘complexes’

Amiri et al. (2008); Haslett et al.

(2001), Moran (2004); Zhang

and Brown (1999).

Source: V. Fernandez, T. Sotiropoulos. P. Brown, 2013

Οκτ-96 Νοε-96 Δεκ-96 Ιαν-97 Φεβ-97 Μαρ-97

25

27

29

31

33

35

37

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41

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Ξη

ρό

βά

ρο

ς σ

ε g

r /1

00

κα

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Ημερομηνία δειγματοληψίαςΟυρία 2%

Μάρτυρας

Θειικό Κάλι 2%

Fru

it d

ry w

eig

ht

(g/1

00 f

ruit

)

DateUrea 2%

Control

K2SO4 2%

Oct Nov Dec Jan Feb Mar

Effect of autumn N and K foliar application on fruit dry weight

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Effect of autumn N and K foliar application on flesh/stone dw ratio

1,10

1,30

1,50

1,70

1,90

2,10

Οκτ-96 Νοε-96 Δεκ-96 Ιαν-97 Φεβ-97 Μαρ-97

Ημερομηνία δειγματοληψίας

Λό

γο

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.β.σ

άρ

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.β.π

υρ

ήν

α

Ουρία 2%

Μάρτυρας

Θειικό Καλι 2%

Ure

a 2

%C

on

tro

l K2S

O4

2%

Date

Oct Nov Dec Jan Feb Mar

Fle

sh

d.w

./sto

ne

d.w

. ra

tio

50

51

52

53

54

55

56

57

58

59

60

61

62

1/10/1996 1/11/1996 1/12/1996 1/1/1997 1/2/1997 1/3/1997

Ημερομηνία δειγ ματοληψ ίας

Ελα

ιοπ

εριε

κτι

κότη

τα %

ξ.ο

.τη

ε σ

άρ

κας

Μάρτυρες

K2SO4 2%

Ουρία 2%

Effect of autumn N and K foliar application on fruit oil percentage (dw)

Ure

a 2

%

Contr

ol

K2S

O4

2%

Date

Oct Nov Dec Jan Feb Mar

Oil

% (

d.w

.)

24/10/2016

56

Thank you for your attention

HELLENIC AGRICULTURAL

ORGANIZATION “DEMETER”

Institute of Olive Tree,

Subtropical Crops and Viticulture

Laboratory of Plant

Mineral Nutrition & Physiology

e-mail: gpsarras@nagref-cha.gr

www.nagref-cha.gr