The onion (Allium cepa L.) is one of the oleraceous species consumed worldwide. In Brazil, onion is the third most important vegetable in economic terms (EPAGRI, 2013).
Cultivation can be done by planting seedlings or direct sowing, and develops best in medium-textured soils (sandy-clayey) rich in organic matter and with good drainage (COSTA, 2010).
The productivity of onion crops depends on the interaction of several factors, among which soil fertility management stands out. Adequate fertilization affects not only productivity, but also the size and quality of onion bulbs, as well as disease resistance (BACK and KURTZ, 2018).
The final productivity of onions depends on initial procedures, such as the addition of organic fertilizer, which has a positive effect on the chemical and physical properties of the soil and should be considered in the fertilization management of the crop to be planted in the same area (BARBOSA, 2007). Organomineral fertilizer is a combination of mineral and organic fertilizers. Organic fertilization allows the recycling of nutrients and the reduction of the use of mineral fertilizers. Organomineral fertilizer restores life to the soil and encourages the proliferation of microorganisms and restructures the soil, which better absorbs the applied nutrients (BEZERRA et al., 2022).
To correct problems and/or optimize nutrient supply, it is important to know the chemical behavior, soil transport, and main chemical forms that are absorbed and transported in the xylem and phloem, influenced by the characteristics of the soil, plant, and environment. Knowing these factors, the growth and nutrient absorption curve of each plant, and the availability and recovery efficiency of each nutrient added to the soil, it is possible to estimate the need for fertilization (MOREIRA et al., 2022).
Fertilization and nutritional requirements of onions
Brazil has large areas of onion cultivation, but to obtain high productivity, it is necessary to improve the efficiency and balance of nutrients in the soil to meet their availability at the time the plant needs them (CASARIN; STIPP, 2013; NOVAES et al. 2007).
During plant development, the nutrients N, P and K (nitrogen, phosphorus and potassium) are absorbed in large quantities and play important roles in plant metabolism (MOREIRA et al., 2022). Nitrogen acts in the formation of proteins and amino acids, enzymes, chlorophyll, synthesis of sucrose, phospholipids and cellulose. Phosphorus acts in respiration, CO fixation2, development of the root system, constituent of nucleic acids and participation in cell division. Potassium acts in the activation of enzymes, in stomatal control and in water conservation (MALAVOLTA, 2008).
Nutrient absorption by the plant is intensified during flowering, in the formation and growth of fruits or reserve organs to be harvested (PORTO et al., 2006). In a study with the Bola Precoce cultivar, Kurtz et al. (2016) considered an average productivity of 37.34 t ha-1 verified the sequence of nutrient accumulation in decreasing order was N > K > Ca > P > Mg > Fe > B > Mn > Zn > Cu, with 101.4; 86.5; 46.6; 34.5; 12.1 kgha-1 and 761; 221; 150; 84 and 34 gha-1, respectively. Of this amount, 68.5 % of phosphorus was deposited in the bulb.
For most vegetable species, N and K are the nutrients most extracted and lost through leaching, often requiring the addition of large amounts of them as fertilizers (PORTO et al., 2006). However, phosphorus is considered the key nutrient in onion production and is related to increased productivity (FILGUEIRA, 2008; GONÇALVES et al., 2019; RESENDE; COSTA; YURI, 2016). Phosphate fertilization is directly related to bulb size and consequently better onion productivity (KURTZ et al., 2018). The combination of mineral phosphate and organomineral fertilization can contribute to the development of a more sustainable and economical fertilization program for the crop (MOREIRA et al., 2022).
The dynamics of phosphorus in the soil is related to environmental factors, physical-chemical properties and soil minerals, and are classified as labile and non-labile phosphates (MOREIRA et al., 2022). The labile fraction is composed of the set of phosphate compounds suitable for quickly replenishing the soil solution, after it is absorbed by plants, while the non-labile fraction is adsorbed in soil minerals. Phosphate fertilization is necessary because in soils, phosphorus is mostly in a non-labile form for the plant, requiring high doses of phosphate to make it available (AQUINO et al., 2021; NOVAES et al., 2007).
At the beginning of the vegetative cycle, restrictions in P availability can cause development problems in the plant, compromising productivity (RESENDE COSTA; YURE, 2016). Onion bulbs respond positively to phosphate fertilization, with greater bulb diameter and productivity (SILVA et al., 2021; WEINGARTNER et al., 2018).
For Lacerda (2021), onion crops are demanding in sulfur (S). The functions of S are related to the plant's metabolism, acting in the regulation, assimilation and synthesis of amino acids such as cystine, methionine and cysteine, which are part of all plant proteins. In addition to being a precursor of volatile sulfur compounds, they act in the photosynthetic and respiratory process of electrons by iron-sulfur agglomeration, making this element essential for the growth, productivity and quality of onions (FORNEY et al., 2010; AGHAJANZADEH et al., 2016). Pungency is the main factor that expresses the quality of onions and is characterized by the combination of their flavor and odor (flavor) (RANDLE, 1997; MIGUEL, 2005).
Pungency is dominated by a series of biologically activated organic compounds derived from sulfuric acid, water-soluble carbohydrates (sugars) and organic acids (SCHUNEMANN et al., 2006). The enzyme alliinase that catalyzes these reactions is stored in the cell vacuole, while the flavor precursors are contained in the cytoplasm, probably in small vesicles. When the cells rupture, the sulfenic acids undergo spontaneous rearrangements and cross-reactions to produce a broad spectrum of strongly aromatic volatile compounds (pyruvate, ammonia and sulfur) responsible for such irritation (RANDLE, 1997; SCHUNEMANN et al., 2006). The higher the sulfur content in the soil, or the increase in temperature, or water deficiency, the greater the pungency of the bulbs (RANDLE et al. 1997; Mc CALLUM et al., 2001).
In Brazilian soil with low S content, Souza et al. (2015) observed productive and quality gains in Perfecta onion. When applying 45 kg ha-1 of S, maximum productivity of 78 t ha was reached-1.
Fertilizer use efficiency can be achieved by implementing the 4C practice by applying the right dose, at the right time, in the right place and at the right time, contributing to the result in economic, environmental and social terms (CASARIN; STIPP, 2013). Actions of this type lead to more sustainable management of the nutrient (REZENDE et al., 2016).
It is worth noting that the presence of organic matter is also essential for the soil because it influences the chemical, physical and biological properties of the soil. According to Novaes et al. (2007), organic matter can be understood as the fraction that comprises all living organisms and their remains found in the soil, in the most varied degrees of decomposition.
Temperature can be a limiting factor for production. Bulb formation is accelerated under high temperature conditions, and under low temperature conditions, the process is delayed. High temperatures (above 32 °C) in the early phase of plant development can cause undesirable premature bulbing. Conversely, exposing plants to prolonged periods of low temperatures (< 10 °C) can induce premature flowering (“bolting”), which is highly undesirable when the aim is to produce bulbs commercially rather than seeds (Figure 1). Temperatures around 15.5 to 21.1 °C promote the formation of better bulbs and higher production (COSTA et al., 2007).
Figure 1 – Premature flowering (“bolting”) in onion. Source: Freitas, 2024.
Larger plants require less time exposed to low temperatures to flower, therefore, cultural practices that favor greater plant growth, such as excessive fertilization at the beginning of the cycle, should be avoided when there is a possibility of very low temperatures (EMBRAPA). Balanced N nutrition combined with the gradual release of this nutrient reduces the risk of this anomaly; products such as ILSA's AZOSLOW can reduce the occurrence of premature flowering ("bolting").
Organic waste influences the availability of nutrients in the soil as it is decomposed (CARVALHO et al. 2014; MARINARI et al. 2006; PAVINATO, PS; ROSOLEM, 2008). This process has the advantage of minimizing nutrient leaching and slowly making them available in the soil solution (Novaes et al. 2007).
One way to return nutrients to the soil is through organomineral fertilization. This fertilization is based on an alternative product, to make production more sustainable, and it also helps in the development of plants and favors soil microorganisms. (MOREIRA et al., 2022).
Organomineral fertilizer
Organomineral fertilization makes production more sustainable. According to Malaquias and Santos (2017), with increasing potential for agricultural use, organomineral fertilizers will have lower costs compared to chemical fertilizers. In a study carried out by Higashikawa and Menezes Júnior (2017), different types of nitrogen-based fertilization (organic, mineral, and organomineral) influenced onion nutrition.
Thus, ILSA can contribute to the productive efficiency of onion cultivation (Figure 2), using GRADUAL Mix in the vegetative production phase, which, positioned via the soil, aims to supply nutrients, proteins and organic carbon to the rhizosphere. This way, there is greater availability of the nutrients contained in the fertilizer, as well as greater biological activity of the soil. Another alternative with application via the soil would be S-TIME, also in the vegetative phase, supplying N and S, proteins and organic carbon to the rhizosphere and aiding in the formation of proteins.
For the reproductive phase, ILSA provides ETIXAMIN Kally with foliar application, acting to supply N, proteins, organic carbon, S and K, which enhances the translocation of sugars and the filling of bulbs.
For top dressing applications, we can use AZOSLOW, applied via soil, providing N, proteins and organic carbon. In addition to easy application, the product increases the availability of N due to the gradual release of organic N present in the fertilizer.
Finally, ILSAMIN Ágile, via foliar application, provides N, proteins and organic carbon. It presents rapid absorption, accelerates plant metabolism and provides greater resistance to abiotic stresses.
Figure 2 – Available ILSA products that can help in onion cultivation.
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Authors
Agr Eng. Dr. Angélica Schmitz Heinzen
Agricultural Eng. Msc. Thiago Stella de Freitas
