The almond tree: cultivation requirements, plant material and nutrition

INTRODUCTION

The almond tree is one of the most important fruit crops in terms of area, after olive groves and vineyards, both in Andalusia and nationally. It has traditionally been planted under poor physical conditions (orography, climate, and soil), and has also been cultivated under dryland conditions.

In a large part of the cultivated area these bad conditions are extreme, giving rise to a marginal cultivation whose production does not exceed 200 kg/ha of almond kernels. The low productivity of these plantations is largely due to the insurmountable limitations posed by poor environmental conditions (poor soils, dry land, etc.), but there is also another negative component due to the relatively frequent management of the crop (insufficient application of fertilizers and phytosanitary products, poor pollination, early varieties that are sensitive to frost and disease, etc.). As in other economic sectors of our society, in recent years, agriculture has had the need to evolve to ensure the profitability of farms. The search for more productive and efficient systems It has therefore been the common objective of many fruit crops.

In countries where the almond tree was more recently introduced, such as the United States, a commitment was made to “intensive” cultivation, under optimal soil and climate conditions, with extensive irrigation and highly technological development. Under these circumstances, they are achieving production levels of around 2.500 kg/ha of almond kernels.

In recent years, the almond tree has gone from being a marginal crop that grew in the poor and arid soils of the Spanish countryside to a alternative production to other fruit trees, to olive groves, to citrus fruits, and even to extensive herbaceous crops. Added to this is the increased demand for almonds, especially in the United States, where California, the world's largest producing region, is unable to supply 100% of its own market demand.

 

This situation, together with other factors, such as the promotion of new varieties late flowering (March and April) that do not suffer the effects of frost, implementation of irrigation (generally in deficit) and the mechanization, have led to a significant shift in almond cultivation in Spain. These new plantations have very different characteristics than those found in traditional plantations, necessitating new cultivation criteria adapted to this type of plantation.

According to FAO (Faostat), the total area dedicated to almond cultivation in 2018 was 2.071.884 ha, being Spain is the country with the largest area devoted to almond cultivation. with 657.771 ha, followed by the United States with 441.107 ha. In terms of production, the United States leads the way with 1.871.500 tonnes, followed by Spain with 337.915 tonnes. It should be noted that in Spain, average yields range between 350 and 400 kg/ha, while in the United States they reach 4.000 kg/ha, due to the more intensive nature of its plantations, the availability of water, the use of high-yielding varieties, and its location on virtually frost-free land.

In Spain, almond production is concentrated mainly in the Mediterranean coastal communities: Andalusia, Castilla La Mancha, Valencian Community, Murcia, Aragon and Catalonia (Figure 1). This production is very variable due to the drought and the incidence of frost, which affect flowering and subsequent fruit setting.

DEMANDS

The almond tree is a typically Mediterranean crop, adapting to very diverse soil and climate conditions. It is able to withstand the high temperatures during the summer and intense cold winter. It can survive long periods of drought periods and be cultivated in very poor lands. However, all these circumstances will negatively affect their production levels, the greater the better the environmental conditions.

Weather

• Temperature

For temperate zone fruit trees, such as almonds, the temperature range optimal for the activity photosynthetic is between 25-30 ºC, with a sharp reduction at temperatures below 15 ºC or above 35 ºC.

For the vegetative period to begin and for correct flowering and fruit setting to take place, some areas must be covered. cold needs winter and, subsequently, heat requirements. To quantify winter cold requirements, the concept of cold hours (HF), which are the number of hours that the tree must spend with temperatures below 7,2 ºCThe almond tree has low HF requirements (between 100 and 400, depending on the variety), similar to those of other typical Mediterranean fruit trees, such as the fig tree or the olive tree.

The almond tree is one of the fruit species more resistant to cold during the winter vegetative stop period, being able to withstand temperatures below -15 ºC. Newly set fruits are the most sensitive organs to frost, followed by flowers and swollen buds.. These organs can be damaged by temperatures slightly below 0 ºC. The almond tree is one of the fruit trees that has the earliest flowering, although, as will be seen later, there are large varietal differences regarding flowering date. Therefore, in areas at risk of frost, special care must be taken to choose late-flowering varieties (Arquero, 2013).

High temperatures can cause serious damage to plants. As mentioned above, Above 35 ºC, photosynthetic activity is seriously reduced., with the trees (especially when they are in dry conditions) entering into what is known as summer vegetative stop. Higher temperatures, above 40 ºC, can cause Dehydration, necrosis and leaf fall, fruit damage and wood burns.

• Pluviometria

Is one of the main productive limitations. Normally, precipitation in countries with a Mediterranean climate is scarce and poorly distributed throughout the year, with a period of water deficit that spans the summer and part of spring and autumn. Added to this is the frequent occurrence of dry years. The almond tree is a crop well adapted to dryland conditions, although its production is increased significantly with the implementation irrigation.

• RH

It is a factor of great importance, since very high or excessively low values ​​of relative humidity (RH) induce the stomatal closure in the plant, negatively affecting vegetative and reproductive activity. Likewise, the incidence of diseases It is highly favored in high RH conditions, which can become a limiting factor for crop implementation.

We can partially control RH within the plantation through cultivation techniques. For example, plantation design and training and pruning systems can reduce tree and canopy density, thereby improving ventilation within the plantation.

• Wind

Strong winds considerably increase the transpiration rate, causing a water stress to the plant. Also enhance the negative effect from extreme temperatures, from minimum temperatures in winter to maximum temperatures in summer. Tree formation is greatly hampered in areas with constant winds. As in rainy or foggy conditions, bee activity is reduced by strong winds, which negatively affects pollination. Finally, very strong winds can cause physical damage to the grove: falling flowers and fruits, breaking branches, which can even bring down entire trees (Arquero, 2013).

In areas with strong and frequent winds, stakes are necessary to ensure the tree's anchorage and upright position in the early years. It's also important to design the planting properly to facilitate air circulation, as well as pruning with adequate intensity to thin the canopy sufficiently so that it doesn't create a screen effect.

Land

• Physical properties

  • • Texture

Heavy or clayey soils can present problems due to poor aeration and limited water mobility. In contrast, they have a greater capacity to retain water and nutrients. Silty soils suffer from similar problems, in addition to a poor structure that favors crust formation and erosion. Sandy soils are highly permeable, barely retaining water or losing it very quickly through percolation. Although they facilitate root growth and the movement of air and water, they are also loose and easy to till, but result in infertile soils with a poor water retention capacity.

 

Heavy soils may present problems of waterlogging and lack of aeration, causing the root asphyxia to which the almond tree is very sensitive. To avoid this, it is recommended to use resistant rootstocks or those with a shallow root system, perform drainage before planting, and/or plant in ridges.

• • • Effective depth

The effective depth of a soil is usually determined by the presence of a water table or a hardpan horizon. The latter may be petrocalcic (accumulation of calcium carbonate), argillic (accumulation of clay), or rocky parent material. All of these represent a physical impediment to deep root development, influencing their ability to extract water and nutrients from the soil. This affects the vegetative and productive stages of the crop, especially in dry land.

Deep subsoiling work prior to planting can significantly improve the usable depth by breaking up petrocalcic horizons, as well as reducing soil compaction or soil erosion.

The almond tree can be grown in shallow soils, although it must always be kept in mind that, The greater the effective depth of the soil, the greater the root development and the higher the availability of water and nutrients., considerably improving the vegetative and productive states of the tree.

• Chemical properties

Among the most important chemical properties of the soil are (FAO, 1984):

• • • Organic material: The optimum should be around 2%, although in many soils where almonds are grown it is common not to exceed 1-1,2%. Therefore, organic fertilization is one of the aspects that needs to be improved in the crop.
    • Carbonates, have a positive effect on soil structure and on the activity of microorganisms, but can reduce crop yields by limiting the response to fertilization when found in concentrations above 20%.
    • active limestone, are fine carbonate particles, very chemically active and which can interfere with the normal development of the almond tree when they exceed concentration values ​​of 9%.
    • pH, greatly influences crop development by determining the solubility of nutrients, the growth of microorganisms, the speed of humification and mineralization processes, and the cation adsorption capacity of the exchange complex. Almond trees tolerate soils with pH values ​​between 5,5 and 8,4.
    • Salinity, measured through Electrical Conductivity (EC), which determines the main cations (sodium, calcium, magnesium and potassium) and anions (sulfates, chlorides, carbonates and bicarbonates) in the soil. The almond tree is a crop relatively tolerant to soil salinity, being able to grow up to EC values ​​of 4 dS/m; however, above 1,6 dS/m, the crop's productive capacity would begin to decline.
    • Fertility levelsA C/N ratio of 10-12 with a total nitrogen percentage (Kjeldahl) of 0,11-0,2 would be optimal for the almond tree.

Irrigation water

The main negative consequences that can arise from the use of poor quality irrigation water are: salinization and sodification from the ground, as well as the phytotoxicity in the plant, which can cause severe damage to the crop and even seriously alter the physical and chemical characteristics of the soil.

A sodium absorption ratio (SAR) greater than 9, chlorine levels above 355 mg/l, and boron levels above 3 mg/l represent a high level of restriction for almond cultivation. The EC of irrigation water will have a greater or lesser impact depending on the SAR, although normal values ​​for this parameter can be estimated to range between 1,1 and 3,2 dS/m (Micke, 1996).

PLANT MATERIAL

As with other fruit species, the almond tree is composed of two individuals: the variety, which is the aerial part of the tree, and the rootstock or pattern, which constitutes the root system.

The current genetic improvement programs were created with the objective of contributing to increasing the competitiveness of the plantations, through the improving the quality of plant material.

Patterns

When choosing a rootstock, the following aspects, among others, must be taken into account: compatibility with the variety, plant uniformity, vigor, plantation longevity, behavior under adverse soil conditions, adaptation to extreme climatic conditions, suitability for the cultivation system (irrigation/dry land, replanting, etc.), resistance to soil-borne pests and diseases, influence on productivity and fruit characteristics.

The most commonly used patterns in almond trees and their main characteristics are (Arquero et al., 2013):

Taking into account the requirements regarding the physical properties of the soil and the sensitivity of almond rootstocks to waterlogging, from Cultifort we propose the use of OXIFORT to prevent and/or recover almond trees that have suffered root asphyxia. It is a long-lasting and effective soil oxygenator, which in addition to improve aeration and water circulation in the root zoneBy providing sponginess and porosity to the soil, it stops the development of anaerobic microorganisms, favoring aerobic and beneficial microbiota, thus improving its fertility.

Variety

Availability Quality plant material is a basic factor in establishing new plantations. Traditional varieties have notable characteristics, but also significant limitations. For example, Marcona and Desmayo Largueta, among the most widely distributed, produce fruits highly appreciated by Spanish consumers; however, they flower early (susceptible to frost damage), require pruning, are sensitive to disease, and so on.

This shows that The variety with the greatest productive potential does not always achieve the highest profitability.Frost, the incidence of pests and diseases, pruning costs, etc., negatively affect the production levels of almond trees. Therefore, the specific objectives of genetic improvement programs have been oriented towards obtaining new varieties taking into account characteristics such as:

• Phenology

The new Spanish varieties are of late or very late flowering, which helps avoid or minimize frost damageThe delay in the flowering date also helps to improve the effectiveness of pollinating agents, being able to increase the setting, since they work in better meteorological conditions (Vargas et al., 2009).

At Cultifort we have already dealt with the problem of frost In previous webinars, we discussed all the principles used to control low temperatures, both before and after planting, including the application of nutritional products and/or biostimulants. In this case, our recommendation was to BVC EVOLUTION (Formerly BVC 2021), metabolic activator of the plant even under adverse conditions (temperature, lighting, wind, etc.), based on amino acids and algae in emulsion. In addition to increasing the resistance to low temperatures and adverse weather conditionsIn general, it helps overcome stressful situations. It increases the rate of photosynthesis, improves the assimilation and translocation of nutrients, increases the synthesis of amino acids, peptides, and proteins, and delays leaf senescence, among many other effects.

 

The flowering date has a genetic and environmental components. Since flowering times for the same variety and year depend on the prevailing temperature regime, they will vary in areas with different climatic conditions. For the same reason, flowering dates for the same variety and location can vary greatly in years with very different climates (Arquero et al., 2013).

It's relatively common to choose varieties that don't fully coincide in flowering dates in self-incompatible multivarietal plantations, resulting in poor pollination and a reduced yield. For all these reasons, flowering time must be an important factor to consider when choosing a variety.

Another important phenological aspect to take into account is the time of maturation, especially in multi-varietal plantations, to establish the degree of phasing that is desired from the collection.

• Compatibility

The almond tree is a species with complete flowers (equipped with the male organs, stamens; and female, pistils) and entomophilous pollination through insects (mainly bees), there are varieties self-incompatible and self-compatible. In self-incompatible varieties, fertilization of flowers with pollen of the same variety is not feasible, while in self-compatible varieties, self-pollination (fertilization of the ovule with pollen of the same variety) is possible. If the self-compatibility trait is complemented by a floral morphology that has an appropriate arrangement of the anthers with respect to the stigma, such that the pollen grains can be positioned on the stigma spontaneously, without the need to be transported by vector insects, the autogamy trait is achieved. self-fertility for a variety (Figure 4).

The character of self-incompatibility requires the implementation of at least two intercompatible varieties and also coincident in flowering, it is advisable to put, at least, one 30% of the surface of the pollinating variety or varieties and the rest of the main variety. Likewise, it is strictly necessary to presence of bees and that, in addition, there are good climatic conditions (absence of rain, wind and fog and not low temperatures) during the flowering period, which allow for good bee activity (Arquero et al, 2013).

With self-compatible cultivars it is possible to carry out single-variety plantationsIf they are also self-fertile, we ensure that pollination is less dependent on insect vectors. Therefore, self-fertility is essential for single-variety plantations and/or those with limited bee presence.

Cultifort's recommendation to improve the activation of the almond tree's vegetative cycle, to achieve a higher quality flowering and more effective setting, is the application of FOLIQUINO. It is a biostimulant rich in energy that thanks to its formulation with organic acids, make it so assimilated by leaves, branches or woody parts and by the root system. Its operation is based on the powerful systemic action of aluminum lignosulfonate, whose mobility, both upward and downward within the plant, helps to balance the aerial part and the root system, improving the sprouting of latent buds and, therefore, achieving a flowering of greater quantity and qualityAmong its functions at the physiological and metabolic level, it stands out for the increase in the synthesis of different metabolites, mainly the polyphenols (activation of the shikimic acid cycle), but also of phytoalexins. Both are part of the natural defense mechanisms of the plant, polyphenols as natural antioxidants, and phytoalexins as an antimicrobial compound with fungicidal and bactericidal action, which help limit the development and proliferation of pathogens. FOLIQUINO also intervenes in the construction of new cellular structures and in the vascular tissue regeneration, making it an important ally in the prevention of wood diseasesIt also promotes nutrient penetration and improves the systemic action of phytosanitary treatments.

 

 

• Ease of pruning

In well-managed irrigated plantations, the trees can reach a large volume. The limiting factor is the lighting and not the lack of water as in traditional dry land. Where there is no light, no fruit is produced. and the branches age more quickly. Varietal vigor, along with the almond harvesting machinery used, will determine the planting pattern.

Both the force such as doors will determine the type and severity of pruning to be applied to each variety. When working with less vigorous varieties that enter production very early, the formation of a good tree structure should take priority over production, to avoid possible tree exhaustion. In contrast, in vigorous varieties, formative pruning can be less intense, to force a rapid entry into production. Furthermore, in varieties with a closed growth habit, the main branches should be forced to open. In contrast, in varieties with a very open growth habit, the most closed main branches should be prioritized (Miarnau et al., 2015).

• disease resistance

There are clear varietal differences in disease susceptibilityThis must be kept in mind in areas where environmental conditions are conducive to the incidence of diseases, since their presence requires a greater number of phytosanitary treatments, and if proper control is not achieved, the damage caused can be considerable.

Figures 5 and 6 show the varietal differences with respect to the incidence of Canker or Fusicoccum (Phomopsis amygdali), the Ochre Spot (Polystigma amygdalinum), (Miarnau et al., 2015).

 

• Productivity

They are given clear varietal differences in production. The cultivars of early flowering they usually have a lower productivity, and those of extra late flowering are clearly less productiveTable 4 shows the productive performance of the main late-flowering varieties.

The almond tree is one of the species with earlier entry into production, being able to reach considerable harvests in the 3rd - 4th year.

However, it is necessary to differentiate the varietal behavior with respect to the precocity of entry into production with that of productive level or potential in adulthood, since they are not always related. Thus, there are very early varieties that have low productive potential as adults, and vice versa.

Another important productive aspect is the degree of alternation of production or alternate bearing (Figure 7). It is always advisable for a variety to maintain a regularity in harvests (Arquero et al, 2013).

• Characteristics of the fruit

Commercially it is desirable that the almond has a high seed weight and a low percentage of doubles, although these values ​​do not currently usually influence the purchase price to farmers.

The commercial value of almond cultivation is fruit seed (almond kernel, seed, or pip). The farmer delivers the almond in its shell, once the shell has been removed. A sample is taken from the delivered batch, and the weight of the pip or seed relative to the weight of the whole fruit (almond shell) is determined. This ratio, expressed as a percentage, is called hull/grain yield, serving to determine the total amount of nugget, on which the settlement is made.

It is common to relate a higher husk/grain yield with a better production level. This statement is wrong, since the production level is determined by the weight of kernel produced per unit of surface area, and is independent of the husk/grain yield. Thus, there are varieties such as 'Cristomorto', which have high productivity with a

low yield; while others, such as 'Supernova', have high yield but medium/low production (Arquero et al, 2013).

NUTRITION AND FATTENING TREATMENTS

Traditionally it has been considered that through fertilization one should restore to the soil the amounts of nutrients that the crop extracted. This method of restitution subscriber presents serious deficiencies that make it inadvisable, the two most important being the lack of response to fertilization when an element is available in sufficient quantity in the soil solution, and the non-quantification of luxury consumption.

It is currently considered that the annual fertilization plan for woody crops should be based on the diagnosis of the nutritional status of the plant, determined by the foliar analysis, which must be complemented with a series of information or references, such as: cSoil characteristics, symptoms presented by the plant, vegetative and productive states and crop management.

Leaf analysis is the best method for diagnosing nutritional status of the tree. It allows for the detection of low nutrient levels before deficiencies occur, establishes the response to the applied fertilizer, and detects toxicity from chlorine, boron, and sodium.

The result of the foliar analysis must be compared with the critical levels of each of the nutritional elements. In the Table 7 The values ​​established for almond trees are listed. Concentrations below the appropriate level cause a decrease in growth and production.

Almond fertilization is primarily carried out through soil application or foliar application.

The traditional and most used form currently is the direct application to soilThe fertilizer thus supplied passes into the soil solution from which it will be absorbed by the roots. This is the system that presents lower efficiency, expressed as a percentage of the element absorbed by the plant with respect to the total applied. The main losses are due to deep leaching and volatilization into the atmosphere. To improve the efficiency of soil fertilization, certain application criteria or recommendations must be followed. Fertilization should be done when the tree is vegetative activity and, therefore, with greater capacity for nutrient absorption, being recommended split the application at two or three times throughout the growing season. The fertilizer must be distributed evenly over the entire surface, since the root system, in adult plants, explores the entire soil. To avoid losses due to volatilization, localized applications should be made. incorporating the fertilizer to the ground through superficial tillage, or it will be applied to the surface immediately before the rains, so that the water incorporates it into the soil.

By foliar fertilization The fertilizer is applied, by spraying, in the form of a nutrient solution to the tree canopy, being absorbed by the leaves. This system allows for a rapid and efficient utilization of nutrients. It is especially recommended for the contribution of micronutrients and in “shock” applications, to ensure a quick response. For greater effectiveness, applications should be made when the tree is in vegetative growth and the leaves are fully expanded; should not be treated with strong winds or high temperatures.

In plantations with localized irrigation, it is recommended to apply fertilizers dissolved in the irrigation water, a technique known as fertigation. This system is that of lower application cost and the one who presents a greater efficiency, since the fertilizer is located in a humid area with a high concentration of roots, so the plant's nutrient absorption is maximum. Furthermore, by incorporating it with irrigation water Fertilizer loss through volatilization is minimalIt is advisable to apply fertilizers as frequently as possible, which can be weekly or daily, throughout the entire irrigation period. This ensures low fertilizer concentrations in the water and maintains constant levels in the soil (Arquero and Serrano, 2013).

It is very important split fertilizer applications, especially nitrogen, which is specifically recommended in spring, summer and autumn, taking advantage of the post-harvest fertilization To provide or replace nutrients that have been found to be deficient in foliar analysis and to ensure the levels of those elements that the almond tree will require in greater quantities during the next flowering period and the start of vegetative growth. Potassium supplements are essential for obtaining good, uniform yields with good-sized fruit and for ensuring production levels for the following year.

In any case, the products, concentrations, methods, and application times permitted or recommended for fertilizer applications must always be respected.

One of the bases of almond nutrition is organic fertilization, the pillar on which lies the improvement of communication between the inert or mineral part of the soil and the plant. At Cultifort we have the best product of the market, within its category, to cover the requirement of organic fertilization. This is MICROVITAL – L, formulated more than 35 years ago and whose results support its good reputation. It is a Organic soil bioactivator of plant origin, rich in magnesium, microelements, organic complexes and flavonoid molecules. In addition to beneficially influencing the physical-chemical and biological aspects (activates the microbiota) of the soil, prevents deficiencies of magnesium and the main micronutrients, induces root formation and the metabolic activityto the plant, protects against the harmful effects of ultraviolet radiation thanks to the flavonoid molecules (polyphenols), which also exert their Antioxidant activity delaying leaf senescence, protecting the plant from adverse conditions and giving it greater resistance to diseases. The organic compounds supplied with MICROVITAL – L, not only complex the nutrients contained in their formulation, but also the nutrients present in the soil, with low mobility or blocked, substantially improving the environmental fertility and nutrition of the plants.

 

Treatments focused on the ripening and fattening of almonds must always be taken into account when we want to obtain high productionsIt's important to keep in mind that starting in spring and after the petals fall, almonds grow rapidly, and any disturbance can affect them. If we've had a significant set, the tree will normally begin to purge the almonds, that is, they'll begin to drop small almonds. This is usually due to several factors, such as:

• Variety:There are varieties that produce more flowers than fruit, and others that produce small almonds.
• NutritionAlmond trees have nutritional reserves of macro and micronutrients from the previous year, so if these reserves are low, it's logical that they will drop more almonds. Hence the importance of fertilization in the final phase of the cycle, post-harvest. Applying nitrogen alone is not enough.
• Irrigation: If there is excess or deficiency in irrigation, it is also a cause of excessive almond fall.
• Wind/Hail: Logically, we will not be able to influence anything here, just have the tree with good reserves so that it costs more work to throw it away.

Regardless of the setting of the tree, we will always have to deal with these moments specific products for almond fattening, if we want to achieve large productions. The reasons are the following:

1. If we have had a poor curdling, at least the almond we have has a big caliber, and consequently we have kilos of seeds that we can defend throughout the year.
2. On the contrary, if we have had a great set and if we do not take into account the nutritional value, the almond will remain small and the weight will be less than expected at first.
3. With small increases in production justify fully applications.
4. In varieties that carry a lot of weight, and the almond is not very large (Penta) it is highly recommended.

La time and duration of treatments It will depend on the variety, climate, area, etc. The general rule is to start applying them when the almond is at least the size of a 20-cent coin, and we would have until the almond shell finally hardens (while the seed is milky). At this point, the skin will no longer grow, and consequently, the almond seed will not be able to grow any further.

In the Cultifort catalogue we have different formulations specially developed for the stages of ripening and fattening of the fruits.

MACROFOL RED PLUS It is a soluble NPK, with a 15-5-30 balance formulated with magnesium and micronutrients. Its composition is designed to promote the development, fattening, ripening and consistency of the fruits, increasing the storage of carbohydrates and proteins In addition, it provides an ideal nitrogen source, with a concentration that does not negatively affect fruit ripening during the phenological stages in which its application is most recommended. MACROFOL RED PLUS It's a product highly soluble, very stable and behaves well in front of the mixtures with other products on the market, does not form lumps During its dissolution, it has a slightly acidic pH and, best of all, it is a fertilizer chlorine-free.

CULTIFORT K y CULTINEUTRAL K, are two liquid potassium formulations de high richness and chlorine-free. They are designed to Promote the process of fattening and ripening of fruits, increasing their size and uniformity, increasing the synthesis and accumulation of sugars and improving color and firmness of the same. Thanks to their formulation technology, they are rapidly assimilated products, with high absorption, mobility, and translocation within the plant. They are similar in terms of richness and their differences lie mainly in the pH, 9 in CULTIFORT K There 6 in CULTINEUTRAL K, and in density, 1,5 and 1,24 kg/l, respectively.

REFERENCES

Arquero, O., Casado, B., Fernández, JL, García, A., Lovera, M., Ramírez, A., Romacho, FJ, Romero, J., Salguero, A., Serrano, N. and Viñas, M., 2013. Plant Material. In Almond Manual (pp. 22-31). Seville (Spain). Ministry of Agriculture, Fisheries and Rural Development. Regional Government of Andalusia.

Arquero, O. and Parra, MA, 2013. Environmental Requirements. In Almond Manual (pp. 16-21). Seville (Spain). Ministry of Agriculture, Fisheries and Rural Development. Regional Government of Andalusia.

Arquero, O. and Serrano, N., 2013. Fertilization. In Almond Manual (pp. 52-54). Seville (Spain). Ministry of Agriculture, Fisheries and Rural Development. Regional Government of Andalusia.

Brown, PH and Uriu, K., 1996. Nutrition deficiencies and toxicities: Diagnosing and correcting imbalances. In Micke, WC Almond Production Manual (pp.179-188). University of California (USA), Division of Agriculture and Natural Resources.

Grasselly, C., and Duval, H., 1997. L'amandier. Paris: Ctifl. Ed.

MAGRAMA, 2018. Ministry of Agriculture, Food and Environment. Statistical Yearbook 2018.

Miarnau, X., Torguet, L., Batlle, I., Romero, A., Rovira, M. and Alegre, S., 2015. Agronomic and productive performance of new almond varieties. National Symposium on Almonds and other Nuts. September 2015. Lleida, Spain.

Micke, W. C. 1996. Almond Production Manual. University of California. Division of Agriculture and Natural Resources.

Vargas, FJ, Romero, M., Clave, J., Batlle, I., Alegre, S. and Miarnau, X., 2009. Important traits in IRTA's new almond cultivars. 5^th International Symposium on Pistachios and Almonds, October, 2009. Sanliurfa, Türkiye. Acta Horticulturae, 912: 359-365.