Avocado

Avocado

The avocado tree is a perennial type fruit specie, which presents a different growing behavior from other fruit trees.

The length and season of phenological stages depend on the variety, climate and geographic place. For the Hass variety, the most cultivated in Chile, the following stages are identified:

Phenological phase

Length (days)

Fertilizer and irrigation

Floral bud break

60

Yes

Flowering to fruit set

60

Only irrigation

Fruit set to small fruit

90

Yes

Small fruit to final caliber

120

Limited

Harvest

30

Yes

 

Nutrients and their role in citrus crops
The application of balanced nutrition aims to ensure adequate aerial and root growth to store as much carbohydrate in specialized organs. Adequate nutrition of the crop is a key factor in obtaining good harvests.

To achieve an appropriate nutrition plan in avocado is necessary to know the nutrient demand in quantity and type of nutrient. It is also important to know the role of each nutrient for crop growth, yield and quality of production.

Nitrogen
Nitrogen is a component of a great number of plant compounds being part of the structural chlorophyll molecule which is present in all proteins. This is the key element for controlling vegetative and reproductive growing balances; in addition, it is the most limiting factor for avocado production.

Nitrogen is the most important mineral nutrient since it determines the avocado production; then management unbalances of this element can generate large vegetative growing in detriment of production.

Nitrogen deficiency symptoms
• Slow plant growing, small leaves of green pale or yellow pale color.
• Initial symptoms on old leave; due to nitrogen is very mobile within the plant.

Nitrogen deficiency on avocado tees
Nitrogen deficiency on avocado trees.

Phosphorus
It is found in organic and inorganic forms in the soil. Inorganic phosphorus comprises chemical available forms in the soil solution. Ionic forms depend on the pH, thus, roots prefer the H2PO4- ion which is predominant in 4 to 6 pH rages; a larger pH value and up to approximately 7.5 is important in presence of HPO42- form. It is estimated that only 20% of the applied phosphorus as fertilizer, is possible to be directly used by the roots, while the rest remain in less available forms, which depend on the pH.

Potassium
Potassium (K+) plays an important role in the activation of enzymes (there are more than 60 of them activated by this cation), which act on divers metabolic processes such as photosynthesis, protein and carbohydrate synthesis. Also, potassium participates in the water balance; besides of having a positive effect by directly influencing the pumping of this element from the soil and on the meristem growing (Mengel y Kirby, 1987). Potassium, by participating in these metabolic processes, acts favoring the vegetative growing, maturity and fruit quality.

Figure: Potassium promotes the photosynthates translocation from the leaf to the fruit, thus in deficiency potassium trees the fruit is smaller, with an opaque color and mort susceptible to sun stroke.

Potassium accelerates the flow of assimilate products to the fruit
Potassium accelerates the flow of assimilate products to the fruit

Potassium deficiency symptoms
The main K deficiency symptom is a marginal necrosis of the leave. This necrosis reaches up to the leaf center from the margins which tends to be bent up ward. Potassium promotes photosynthates´ translocation from the leaf to the fruit, thus the potassium deficient trees have smaller fruits, with opaque color and more susceptible to sun stroke.

Potassium deficiency on avocado trees.

Calcium
El Ca2+ differs from the majority of other nutrients due to that generally deficiency symptoms are developed in specific plant parts, in stead of affecting the total plant growth. This reinforces the Ca characteristic of having a limited mobility within the plants, which are not able to easily transport this element from the tissues with adequate Ca to those with deficient levels (fruits). To obtain quality fruit is based on two components: internal quality (Ca level and post-harvest fruit life) and external quality (color, size, shape, friction and spots present on the fruit) determined by physiological disorder susceptibility, disease resistance, softening, among others.

Calcium physiology
Most orchards have a great variation in Ca levels from one year to the other. This means that the fruit farmer must be always concern to Ca deficiencies; he never should think that there is no problem. Low Ca level in fruits should not be a supply problem and/or a Ca deficit absorption from the soil, but it is a distribution problem within the plan. Therefore, Ca level measurements in the soil or in the vegetative parts of the plant (foliar Ca) are not adequate indicators of Ca present in fruits.

Young fruits (cellular division period): Ca is absorbed by roots and transported by the transpiration flow (Xylem via).

Grown fruits (cellular expansion period): Ca is transported by the respiration flow via toward the high transpiration organs (leave) by the xylem via. But Ca cannot be re-transported to the fruit since it is not mobile within the phloem. Even though, an option in this stage is externally applying Ca to be absorbed by the fruit skin.

Calcium concentration in the fruit significantly varies according to the variety and tree’s vigor. For avocado Hass variety, Ca ranges between 1,300 to 1,650 ppm, from fruits of no vigorous and vigorous trees, respectively.

Fruit position on the tree, also affects the Ca distribution. The fruit that grows under sunny situation can easily reaches pulp temperatures from 35 to 45° C, during three or four months during the growing period, generating high transpiration rates for the fruit. Thus, a greater supply of Calcium, Magnesium and Potassium is favored, which are minerals translocated from the root absorption by the xylem flow. In addition, an adequate summer pruning, allows a greater light incidence and heat within the canopy.

The companion ion has also influence in the Calcium absorption. NH4+, K+ and Mg+2 cations depress the Ca absorption, while NO3 anion, followed by Cl- and SO4-2 favor its absorption; a balance between these elements allow a good Ca accumulation.

Ca is one of the most determinant minerals of fruit quality. In avocado, it has been observed that the Ca concentration is positively related with a greater resistance to degradation of cellular membranes, which implies a larger post-harvest life.

Magnesium
This macroelement is the central component of the chlorophyll molecule, thus, it is essential for the photosynthetic process. From the total Mg content within the plant, between 25 to 30% form part of the chlorophyll molecule.

Mg present a positive charge (cation), therefore it can fixed in clay soils, the same than potassium and calcium, reducing the supply toward the plan. Acid pH soils also present Mg deficiencies.

Mg deficiency symptoms:
Mg deficiency is characterized by an internal chlorosis (chlorophyll disintegration), from a bronze aspect which take a V shape. This is initiated in the older leave base, advancing toward the center and covering the margins.

Mg deficiency in avocado trees.

Boron
B moves from the roots with the transpiration flow through the xylem. Once in the leaves, B re-translocation is restricted and it remains forming part of the cellular walls, providing elasticity. Furthermore, B concentrations into the phloem would be low, existing continuous B accumulation in the leave and presenting symptoms in the plant meristem tissues. As a result, it has been concluded that boron is a immobile element in the plants´ phloem; even though, studies with marked B have proven that in divers fruit trees of the Rosaceous family, foliar post-harvest applications have increased the concentration of this element in the leaves and that part of B was mobilized toward the bark of the sprouts. Then, during spring, B was translocated through the phloem from the bark toward the flower and increased the fruit set. This mobility of B in fruit trees would be possible since these species translocate carbohydrates in the form of sugar-alcohol (sorbitol), which is able to be associated with boron and facilitates its transport.

Deficiency symptoms in fruits can be appreciated as necrosis and deformations in the fruit shoulders.

Boron deficiencies in fruits of avocado trees.
Boron deficiencies in fruits of avocado trees.
Nutritional Recommendation
An adequate supply of nutrients to plants should incorporate both macronutrients and micronutrients. SQM in the selection of specialty plant nutrition (SPN) that offers the following alternatives available according to the route of application (fertigation, soil or foliar):

This is the nutrients´ quantity that a plant must absorbed from the soil solution for reaching a determine yield. This figure includes the present nutrients in each part of the plant: leaves, stems, roots and tubers.

Nutritional requirements of any crop are determined by the total nutrients needed to be extracted during its physiological development. Now, this extraction is not constant, it differs according to the development or phonological stages. Therefore, in order to determine the best nutritional strategy, it is necessary to identify which are the phenological stages and their demands.

Macronutrients extraction of avocado tree fruits (kg/ha) with 10 ton/ha yield.

N

P

K

Mg

Ca

S

11.3

1.7

19.5

5

2.1

8

Source : Lahav, E 1995.

It is important to emphasize that the potassium extraction is similar and even greater than nitrogen, showing the importance of potassium nutrition in avocado trees.

Micronutrients extraction of avocado tree fruits (kg/ha) with 10 ton/ha yield.

B

Cu

Mn

Zn

Fe

0.04

0.01

0.02

0.04

0.09

Source : Lahav, E 1995.

In general terms, it is estimated that for a 10 ton/ha harvest, the fruit extracts around 28 kg of N/ha/year. An annual vegetative growth increment between 20 to 30% could cost between 14 to 21 kg of N/ha.

Absorption efficiency of nutrients.

This is the absorbed quantity of a nutrient by the plant from the total specialty plant nutrient applied. This depends, mainly, on the source of the specialty plant nutrient (solubility, availability, etc.), roots´ sanitary stage, soil conditions such as humidity, temperature, pH, and the irrigation system (traditional or dripping).

Foliar Nutrition in avocado trees.

Given the soils´ variability and the high interaction of factors that can avoid an adequate nutrients´ absorption by the roots (sanity, salinity water excess and/or deficit, etc.), it is necessary a foliar complementary supply for preventing and/or correcting nutritional deficiencies. This is for assuring an adequate nutrients supply according to plant requirements.

On the other hand, the use of bio-stimulant products and/or bio-regulators, allow stimulating plants in key moments of their development, achieving specific objectives such as rehabilitating plants from temporal stress, promoting a greater roots, sprouts, leaves and/or fruit development.

Foliar application via Speedfol™

Growth Stage

Product

Dose / 100l (ml or gr)

Product use/ha (l or kg)

Observations

Shooting and shoot growth

Speedfol™ Mg SC

200ml

6,5 l

To increase photosynthetic efficiency.

Speedfol™ Zn SC

100ml

2,0 l

Repeat every 10 days. 2-3 applications

Speedfol™ Zn+Mn SC

200ml

4,0 l

During shoot growth to improve the leaf quality

Preflowering

Speedfol™ Amino Starter SC or Speedfol™ Amino FLower & Fruit SC

350ml

5,0 l

Products can be applied together as indicated.
Speedfol™ Amino Starter SC has a high Phosphorus content to promote flowering and flower quality.
Speedfol™ Amino Flower & Fruit SC to promote fruit set.
One application according the weather conditions and growth stage of the new shoots.

Speedfol™ B SP

100gr

2,0 kg

Speedfol™ B SP improves the fruit set, which results in more fruits per hectare.
Products can be applied together as indicated.

Inflorescence (10% of the flowers open)

Speedfol™ B SP

100gr

2,0 kg

One application according the weather conditions and growth stage of the new shoots. Speedfol™ B SP improves the fruit set, which results in more fruits per hectare.

Around flowering (just before or just ofter)

Speedfol™ Zn+Mn SC

100ml

2,0 l

Stimulates fruit set, fruit calibre and shoot growth. Apply just before or just after flowering.

Fruit set

Speedfol™ Amino Calmag SL

500ml

10,0 l

Aplicar durante el nuevo desarrollo foliar y antes que los tejidos de las hojas lignifiquen. Tres aplicaciones cada 7 dias.


The recommendations in the table are general: They can vary by several factors, conditions, criteria and objectives. Ask your adviser or distributor for your nutritional program or any other specific information about using the range of nutrition products Speedfol™.
Soil
Light texture, deep and well drained soils are the most recommended. But also clay or clay loam soils with good drainage can be cultivated, since the moisture excess is an adequate medium for inducing root physiological diseases, root asphyxia and fungi such as Phytophthora cinnamomi.

On the other hand, hillside avocado plantings are frequently conducted in order to avoid frost damage. This situation increases the possibility of having a deficiency on those nutrients which are concentrated on the soil surface. Soil leveling works and terraces´ formation may induce Potassium and Boron deficiency, which finally is the factor that limits the production of this crop.

Avocado trees are developed in soils with neutral to light acid pH (5.5 to 7), with the condition that there are no salts or Sodium accumulation problems. These problems must be carefully managed due to that significantly affect yield.

The figure clearly shows the greater nutrients´ availability of the soil with pH near to neutrality (6.5 a 7.5) and the larger retention of these by the soil as the pH moves away from 7.0. Thus, a more adequate nutritional program must be adopted for a specific pH value in the soil. Possibly, Phosphorus is the most typical case of nutrient retention by the soil.

Figure: Influence of pH on the soil nutrients´ availability.
Figure: Influence of pH on the soil nutrients´ availability.
Sol salinity effect
The electric conductivity is the first concept that should be considered, which is utilized as indirect measure of salt concentration of soils and waters. As greater value, a negative response is produced on the crops. The expression units are dS/m or mmhos/cm, both are equivalent.

This must be interpreted in the following way: The avocado crop can reach up to 100% of its productive potential with an electric conductivity up to 1.3 mmhos/cm in the soil.

It is considered that, if the soil has an electric conductivity of 2.5 mmhos/cm, crops can only obtain up to 75% of their productive potential. This means that it is expected 25% less yield due to a greater salt level which the avocado crop is able to tolerate.

(Values expressed in mmhos/cm, Saturated Paste)

Tree Crops

100%

90%

75%

50%

Avocado

1,3

1,8

2,5

3,7

Figs

2,7

3,8

5,5

8,4

Olive

2,7

3,8

5,5

8,4

Orange and lemon

1,7

2,3

3,2

4,8

Peaches

1,7

2,2

2,9

4,1

Apricot

1,6

2,0

2,6

3,7

Almond

1,5

2,0

2,8

4,1

Table. Percent yield obtained according E.C. - Source: Water quality for irrigation, 1977, page N° 141.
Ultrasol® and Speedfol™ B SP help to control plant vigour

In Mexico, around 127.000 hectares are under avocado. The predominant variety is Hass, and there is a strong move to high density planting. In intense orchards, vigour control is a significant challenge to ensure that overcrowding does not quickly occur and to sustain high cropping levels ... Read More.

Phenological Stage



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Disclaimer:
All the information is given to the best of SQM's knowledge and is believed to be accurate. Your conditions of use and application of the suggested products and recommendations are beyond our control. There is no warranty regarding the accuracy of any given data or statements. SQM specifically disclaims any responsibility or liability relating to the use of the suggested products and recommendations and shall under no circumstances whatsoever, be liable for any special, incidental or consequential damages which may arise from such use.