The almond tree is generally considered a rustic crop, very tolerant to drought (Torrecillas et al., 1989) however, producers are tremendously dependent on the supply of water and nutrients to obtain high yields of optimal quality in their crops (Micke, 1996).
El Establishing a reference fertilization program is essential to allow for the expression of productivity, to achieve good development, and to avoid, or at least reduce, alternate bearing (Salazar and Melgarejo, 2002). However, these types of programs must be adapted to the specific characteristics of the plot and carried out after analyzing the soil, pruning yield extractions, and leaves.
Gruhn et al. (2000) and Tagliavini and Scandellari (2012) insist on the need to understand the so-called “nutrient cycles” as a continuous recycling of nutrients to and from the soil, which involves biological and chemical interactions and which, to date, remain not fully explained (Hamdi and Abadia, 2013). The cycle includes inputs that add nutrients to the soil such as mineral fertilizers, organic matter, atmospheric deposition, biological nitrogen fixation and sedimentation., in addition to extractions which include both harvest and other losses from the tree, as well as nutrients lost through leaching in the form of gases or erosion.
The most common foliar nutrient contents according to sources from the Ministry of Agriculture, Fisheries and Food are described in the following table:
Fertigation facilitates the progressive absorption of nutrients in small amounts at the root level and allows adaptation to each stage of the crop. It also promotes a better response in both productivity and quality of the almond tree (Valverde et al., 2006).
With regards to basic importance of each of the main nutritional elements In the almond tree, the following are worth highlighting:
- Nitrogen: Bruulsema et al. (2008) describe nitrogen as a common element that is important in the initial growth of the tree Since it promotes vegetative growth, almond trees typically have relatively low nitrogen requirements, in dryland areas it is a vital element for proper fruit development.
- Phosphorus: Phosphorus is an element key in energy transportation, is part of nucleoproteins and is involved in vital functions such as photosynthesis and cell division among others (Muncharaz, 2004). Salazar and Melgarejo (2002) highlight the importance of this element in root formation by promoting the development of meristems.
- Potassium: potassium favors the concentration of assimilates in the fruits, hence a potassium deficiency limits fruit size (Reidel et al., 2001). It is an essential element for tree growth as it activates a large number of enzymes and plays a key role in leading role in water relations of the same and also improves plant resistance to pests and diseases. (García-Serrano et al., 2010).
- Boron: Although boron is a trace element that is low in requirement for the almond tree, Its lack implies a very considerable increase in floral anomalies. Despite being a mobile element whose Foliar fertilization is very efficient In this species (Brown, 2007), Salazar and Melgarejo (2002) recommend that The tree's needs must be met before budding.
- Zinc: similarly to boron, Zinc is an important element in almond blossoming. Sotomayor et al. (2001) highlight the action exerted by foliar application of a combination of boron and zinc in almond curdling.
To optimize almond production, it is essential that the flowers set and the fruits, which contain the seeds or almonds, develop properly. To achieve this goal, all events must occur without limitation, ranging from flower bud formation, flowering, pollination, fertilization, fruit set and development, and fruit maturity (Sotomayor, 1997).
Almond fruit setting is associated with factors occurring during flowering., both environmental and limiting: temperature, relative humidity, lack of rain, efficient work of pollinating insects, Nitrogen (N), Carbon (C), Boron (B) and Zinc (Zn) reserves, among others; as inherent to the fruit species itself: adequate combination of compatible and matching pollinating cultivars (Grasselly and Crossa-Raynaud, 1984).
The conditions the plant faces after fruit set also determine the final harvest. Since the almond tree is an edible seed, it is important that as many fruits set as possible and persist until harvest, in order to finally obtain their seeds. Therefore, both fruit set and subsequent fruit maintenance throughout each season are essential for the productivity of this fruit tree. setting levels considered suitable for almond trees, fluctuate between 20 and 30% (Nyomora et al., 1997). However, it is possible to find setting levels from 5 to 50%, depending on the agroclimatic conditions of a plantation (Hill et al., 1985).
Corrective foliar applications of B applied at harvest, they got increase fruit set by 26 to 59% compared to a control treatment without B applications (Nyomora and Brown, 1999).
In various fruit trees it has been determined that Low levels of B can restrict fruit set, reduce their retention and development and reduce crop yields (Sotomayor and Silva, 1999). The vast majority of trials carried out in this regard have been with trees that did not show B deficiency, so it is assumed that there is a specific and localized requirement of this micronutrient in the reproductive process of many fruit trees (Nyomora et al., 1997). In this sense Silva and Rodríguez (1995) point out that B may be present in an adequate concentration in leaves or other organs, but deficient in meristematic or floral tissuesThe action of B in the flowering and fruiting processes seems to be indirect and determined by other mechanisms in which this microelement participates, such as absorption and transport of ions and carbohydrates in the plant (Parr and Loughman, 1983).
A deficiency of “B” would alter the transport of sugars to the developing flower, reducing the sweetness of the nectar and making it less attractive for bee pollination (Marschner, 1986). It is also postulated that B influences the flavonoid synthesis, compounds related to the viability and germination capacity of pollen (Taylor et al., 1994).
Nyomora et al. (1997) point out in this regard that B deficiencies determine lower pollen viability and germination and a reduction in the pollen tube development rate, while Silva and Rodríguez (1995) consider that deficiency symptoms are normally a greater flower abortion and imperfect setting, among other problems. On the other hand, Lewis (1980) mentions that B plays a physiological role in the inactivation of callose, an element that usually hinder the penetration of the pollen tube in the floral style of different fruit trees, especially between incompatible cultivars.
Another element that has been Zinc is associated with fruit productivity.. The classic symptoms of Zn deficiency are small, rosette leaves, shortening of internodes and in severe cases, defoliation and death of twigs. In general terms, the action of Zn in plants consists of activate various enzymatic processes, such as the phosphorylation of glucose, thus allowing the formation of starch, peptidases and the transformation of amino acids into proteins (Silva and Rodríguez, 1995).
Zn is involved in the formation of auxins through the synthesis of tryptophan, their precursor, therefore, the deficiency of this micronutrient is revealed by a drastic decrease in the levels of auxins in the plant and they also exhibit greater activity of indoleacetic-oxidase, which degrades the existing indoleacetic acid. Auxins play a fundamental role in the growth of leaves, shoots and fruits in plants..
Some authors point out that there is a Effect of Zn on fruit set and weight. Viveros (1996) considers that, in almond trees, deficiencies of Zn and B cause irregular growth of the plant and its fruits, excessive fall of these and lower harvests. According to Brown and Uriu (1996), the delayed flowering of almond trees due to the lack of Zn, usually determines poor pollination it's important reduction in production of fruit. They also note that almonds produced on trees deficient in Zn are smaller than normal.
It is already common in almond trees to carry out Foliar applications of B and Zn from ripening to post-harvestThey are also carried out during flowering, but their effectiveness is not proven.
The post-harvest boron applications, are very effective, since it is a very mobile element, which It is stored and remains in high concentration until the next flowering, improving fertilization and therefore setting. The zinc, of great importance in the growth and germination of pollen, must be Applied post-harvest only when foliar analysis values are low or when fruit species are very demanding of this element, as is the case with the almond tree.
For all these reasons, the Cultifort technical department would like to recommend a series of products to improve flowering and fruit set in almond trees:
MICROVITAL-LLiquid formulation of organic molecules of plant origin with magnesium and microelements. It beneficially influences the biological, chemical and physical aspects of the soilOrganic matter is essential for soil life, promoting the development of the microbiota. It improves aeration, infiltration capacity and water retention, increases the carbon/nitrogen (C/N) ratio and with it soil fertility, improves the clay-humus complex, cation exchange capacity (CEC) and nutrient availability, facilitates root formation and metabolic activity of plants and delays leaf senescence, helping the plant to remain photosynthetically active for a longer time, which will lead to a greater accumulation of reserve substances. It also prevents the main microelement deficienciesThanks to its flavonoid molecules, magnesium, and microelements, it provides a unique advantage to crops.
CULTIBORO PLUS. Liquid boron formulation, complexed with ethanolamine and reducing sugars, for easy assimilation. Recommended for improve flowering (pollen tube and pollen quality)) and the curdling, as well as to induce root growth and renewal of absorbent hairs, because it is involved in cell division and acts as precursor of certain hormones. This element is often found in deficient levels in calcareous and easily leachable soils or in light soils, which leads to its deficiency.
MANZIFORT. Liquid formulation rich in zinc and manganese chelated with EDTA, polycarboxylic acids, and reducing sugars. Ease of application, rapid action, and effectiveness are the main features achieved with this simultaneous zinc and manganese corrector, as they are deficiencies that are usually associated in many crops, making it advisable to control them together. zinc acts mainly as enzyme activator, highlighting the auxin synthesis (indoleacetic acid or growth hormone); while the manganese It is another enzyme activator related to the metabolism of carbohydrates and fatty acids, as well as in the formation of nucleic acids and in the Krebs cycle, and together with other metals, it is Arginase and phosphatase activator, in addition to acting in the photolysis of water in photosynthesis.
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