The importance of Silicon in agriculture

Do you know the benefits of silicon (Si) in agriculture?

 

1. It reduces transpiration and water loss by plants, improving the water regime in drought conditions.
2. Protects against the harmful effects of ultraviolet radiation and excessive radiation, protecting fruits from the dreaded "sunburn"
3. It provides mechanical strength to the cell wall, hardening plant tissues. This prevents conditions such as lodging in cereals or the bites of sucking insects in countless crops.
4. It acts on the plants' self-defense system, activating the synthesis of molecules with high defensive power, such as enzymes and phytoalexins.
5. It therefore acts against pests and diseases through both physical and chemical mechanisms, reducing their impact on plants.

 

1. INTRODUCTION

 

There are 17 essential elements for plant growth, grouped into organic and inorganic. The former include oxygen (O), hydrogen (H) and carbon (C), non-mineral elements, which plants obtain from the carbon dioxide (CO₂) of the atmosphere and soil water. The CO₂ and water are combined through the process of photosynthesis giving rise to the formation of carbohydrates, main power source cell phone and structural constituents of the carbon skeletons of numerous organic molecules in plants. The other elements correspond to the mineral nutrients which are classified into macronutrients and micronutrients, according to their concentration in plant tissues. Macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Micronutrients include boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn) (Kirkby, 2012).

 

All of them are considered Essential elements because they meet the three essentiality criteria proposed by Arnon and Stout (1939) and which are:

1. The absence/deficiency of the element in question prevents the plant from completing its life cycle.
2. The function of the element in the plant cannot be replaced by another element, that is, it must be totally specific.
3. The element must exert its effect directly on the growth or metabolism of the plant.

 

There are other elements that are not essential for plants but that can promote growth and development and improve some of its characteristicsThey are the so-called beneficial elements (Broadley et al. 2012), among which is silicon (Si), which has been reported to improve the physiology of numerous species and perform various structural and biochemical functions (Ma, 2004).

The scientific literature of different countries collects the Beneficial effects that Si can provide on plant-environment relationships in a wide variety of crops, from enhancing growth and yield to more complex actions such as improving resistance to metal toxicity, salt stress, drought resistance, herbivore resistance and disease, suggesting potential use in agriculture (Zia-ur-Rehman et al. 2016).

 

In plants, Si allows the biochemical activation of defense genes, enzymes and phytoalexins, and at the same time allows anatomical changes in the structure of cells, providing mechanical resistance to tissues, which together can give the plant better ability to withstand adverse abiotic conditions such as salinity, drought, flooding, cold, and excessive radiation. Also to adverse biotic conditions, such as diseases and pests (Ma et al. 2001).

 

2. MECHANISMS OF ACTION OF SILICON 

 

Stress is the consequence of any external factor that negatively influences the plant and can limit its functioning (Rejeb et al. 2014). Stresses can be classified as physical, chemical, and biotic, with physical and chemical stresses being grouped under the term abiotic stresses (Tambussi, 2004). Among the physical factors that can induce stress in the plant can be mentioned UV radiation, high and low temperatures and water deficit or excess. In relation to the chemical factors found air pollution, heavy metal toxicity and salinity. The biotic stress It is caused by the action of different living beings such as harmful insects, parasites, weeds, bacteria, fungi, nematodes and viruses (Orcutt and Nilsen, 2000; Redondo-Gómez, 2013).

 

Throughout evolution, Plants have developed different responses and adaptations that allow them to survive under stress conditions. (Cardozo and Quiriban, 2014). Many of these adaptations are related to the role played by both essential and beneficial nutrients (Huber, 1980) where It is worth highlighting the role of Si in the tolerance of stresses suffered by plants. (Yavaş and Ünay, 2017).

 

In biotic stress, Si serves as a mechanical barrier that prevents pathogen infection and allows tolerance to attack by phytophagous insects. (Ma, 2004). On the other hand, the same mechanical barrier reduces perspiration stomatal and cuticular contributing to reduce water loss by plants, while maintaining a greater stomatal conductance and water potential that, consequently, optimizes photosynthetic efficiency. All this explains the positive impact of this element against the damage caused by abiotic stresses, mainly those produced by salinity and drought (Sacala, 2009).

Regarding the chemical barrier, Si has been proposed to play an active role in enhancing plant defense mechanisms at the biochemical and molecular levels. It promotes the production of phenolic compounds and increases the levels of some classes of phytoalexins, as well as the transcription of some genes that code for proteins related to plant defense against pathogens, the so-called PR proteins (Rodrigues and Datnoff, 2005).

 

3. 1. EFFECTS ON TOLERANCE TO ABIOTIC STRESSES

 

3. 1. 1. WATER STRESS 

 

One of the strategies to increase plant survival and yield under water stress is mineral nutrition management (Hu and Schmidhalter, 2005; Marschner, 2012). In this regard, there is clear evidence that The application of Si fertilizers to crops shows positive effects against damage caused by drought. (Sacala, 2009). Among them it has been observed that promotes gas exchange, which is one of the processes most sensitive to this type of stress. It has been shown that under these circumstances Si plays a protective role in the chloroplast, as well as a improvement in the concentration of pigments related to light absorption resulting in a increased photosynthetic activity (Cao et al. 2015; Jesús et al. 2018). In addition, Si in the plant seems to favor the presence of organic compounds, which contribute to osmotic adjustment allowing the plant to retain water and thus maintain vital processes such as photosynthesis (Matichenkov, 2008 and Matichenkov et al. 2008).

 

Leaf transpiration occurs primarily through the stomata, although a small portion may also occur through the cuticle (Figure 1). Since Si can be found beneath the cuticle, forming a dense layer by the deposition of amorphous silica, water loss through transpiration, both in cuticular transpiration and that carried out by stomata, is reduced by the formation of this layer (Ma, 2004). In addition, Si is involved in the synthesis of other proteins involved in plant tolerance under drought, such as ion transport proteins and those that allow the transport of water, aquaporins or even proteases and phosphatases (Sapre and Vakharia, 2016; Coskun et al. 2016).

 

As examples, rice, a Si-accumulating plant, tends to have leaves with a thin cuticle, but Si accumulation can reduce the transpiration rate by approximately 30% under drought conditions (Ma et al. 2001). In maize plants, Si application appears to improve grain growth and yield under drought conditions, which has been attributed to an improvement in the photosynthetic rate, resulting in lower plant transpiration (Amin et al. 2018). Research on cocoa and strawberry crops treated with Si showed an increase in the photosynthetic rate and stomatal conductance, accompanied by an increase in water use efficiency (Zanetti, 2016; Dehghanipoodeh et al. 2018).

 

3. 1. 2. SALT STRESS 

On the other hand, the increase in the levels of Si fertilization in plants, manages to be a effective protection mechanism against the harmful effects caused by salt stress, which can be an alternative for agricultural production in soils and water with salinity problems (Zhu and Gong, 2014).

 

The harmful effects of salinity on the growth and development of the plant are summarized, mainly, in three categories: effects on water relations, nutritional effects and effects on energy balance (Pasternak, 1987), which consequently manifest themselves in alterations in the main metabolic processes of the plant such as germination, growth, gas exchange, etc. (Poljakoff-Mayber, 1975).

 

Plant growth under saline conditions causes the reduction of water potential of the soil solution, which causes a decrease in water absorption by the roots. In this case, the plant's response consists of increasing the intracellular production of soluble compounds, which decrease the intracellular water potential and facilitate the entry of water; otherwise, not only would water from the external environment not enter, but it would tend to leave the root cells, and the plant would dry out (Gárate and Bonilla, 2008).

 

The accumulation of Si in the different tissues of the plant, especially in the leaves, they represent an effective physical barrier that effectively reduces water loss through transpirationThis has as a direct consequence a lower absorption of sodium and chlorine and lower transport of these salts through the xylem (Ahmad et al. 1992), and as an indirect consequence, an increase in the concentrations of potassium, calcium and magnesium (Liang, 1999; Liang et al. 2006; Sahebi et al. 2015).

 

For Méndez (2019), Yes can promote the increase of different osmotic compounds in the plant, such as proline, soluble proteins, sugars and phenolic compounds, which allow the osmotic adjustment by decreasing the water potential of the tissues, thus reestablishing the gradient between soil and cells and, as a consequence, greater water uptake and retention in the tissues.

Examples of such effects include rice trials, where Yeo et al. (1999) correlated Si supply to plants with a reduction in transpiration rates, leading to improvements in gas exchange parameters in plants under salinity conditions; in wheat, Tuna et al. (2008) reported that reduced Na and Cl uptake, and consequently, decreased transport from roots to leaves, led to improved plant growth in saline environments with the presence of Si; while Osman et al. (2017) and Ahmad et al. (2019) reported that the protective effects of Si supplementation in these plants against salinity were due to increased levels of osmolytes, such as carbohydrates and amino acids like betaine, glycine, and proline.

 

3. 2. EFFECTS ON TOLERANCE TO ABIOTIC STRESSES

 

3. 2. 1. DISEASES

 

The severity of many plant diseases can be reduced by improvements in mineral nutrition management.. This can be achieved by modifying the availability of a particular element (Huber and Haneklaus, 2007). In this case, it is considered that increases in Si fertilization of the crops can be effective in improving disease tolerance caused by fungi, bacteria, nematodes and viruses due to the formation of mechanical barriers and/or changes in the plant's chemical responses (Sakr, 2016; Yavaş and Ünay, 2017). The positive role of Si in mitigating the detrimental effects caused by diseases in crops is attributed, in part, to its accumulation and polymerization in the tissues of the epidermis (Pozza et al. 2015). This accumulation forms a thick layer, which protects and fortifies, constituting an effective physical barrier that hinders the direct penetration and development of pathogen hyphae in plants. (Debona et al. 2017), as shown in Figure 2.

 

 

On the other hand, there is a hypothesis that the Si present in the plant also forms chemical and biochemical barriers, thereby activating the natural defense system of the plant when infected by a pathogen (Fauteux et al. 2005). Plants attacked by pathogens can generate enzymes with the function of degrading the cell wall of phytopathogenic fungi (Rodrigues et al., 2001) and low molecular weight secondary metabolites, such as flavonoids and phytoalexins, in addition to other compounds such as glycosylated phenols, which together have antifungal properties and play a very active role in disease suppression (Fawe et al. 1998; Rodrigues et al. 2004).

We will highlight some examples of fungal disease prevention with foliar or direct applications of Si. In pears, the severity of diseases caused by Penicillium expansum and Botrytis cinerea was significantly reduced, suggesting that the element has a positive effect on the postharvest quality of pears. (Corrêa et al. 2017)In peach fruits, the use of Si as a pre- and post-harvest treatment agent induced tolerance to Monilinia frutícola attack and was accompanied by significant increases in total polyphenol synthesis and fruit pulp firmness. (Pavanello, 2016). In rice and grapevines, the action of the physical barrier against the penetration of fungi that cause blight and mildew, respectively, has also been observed in plants where there was treatment with Si. (Bowen et al. 1992; Kim et al. 2002)In another post-harvest study, it was shown that the use of Si promoted tolerance to powdery mildew attack caused by Podosphaera xanthii, followed by increases in the firmness of melon fruit pulp. (Cruz, 2016).

In bacterial diseases, Si also provides protective functions. In rice and banana plants treated with Si and inoculated with Xanthomonas oryzae and Xanthomonas wilt, respectively, an increase in PPO and PAL activities was found, associated with a reduction in bacteriosis, in addition to increases in the contents of phenolic compounds and lignin in rice leaves. (Song et al. 2016; Mburu et al. 2016). In melon, a clear tolerance of plants against the attack of bacterial spot has been found when Si has been supplied. (Ferreira et al. 2015).

 

3. 2. 2. PESTS

 

The Yes can effectively contribute to improve plant tolerance to insect attack, since many of the defense mechanisms produced by plants supplemented with Si against diseases work in a similar way to those generated when the plant is attacked by insects (Alhousari and Greger, 2018).

 

El The first mechanism is based on the physical barrier hypothesis, since Si is deposited in tissue cells, including epidermis and cuticle in the cell wall forming a rigid double layer of silica, which affects important processes, including hinder infection and penetration of insect stylets (Reynolds et al. 2009).

 

The second proposed defense mechanism is that Si supplements when plants are attacked by insects, increase the release of defense enzymes such as POX, PPO and PAL, which induce in plants a Increased production of secondary metabolites involved in lignification and the synthesis of suberin, which increases hardness and decreases the digestibility of plant tissues.. Consequently, they generate a decrease in insect preference (Keeping and Kvedaras, 2008).

 

Apart from this, Si also favors increases in the synthesis of production of volatile compounds that attract natural enemies of insects and is also involved in the differential regulation of genes related to plant defense (Thaler et al. 2002, Liu et al. 2017). For Massey and Hartley (2006), the increased stiffness of the leaves due to Si deposition decreases palatability and digestibility for both vertebrates and invertebrate herbivores. It can also cause wear of mouthparts, leading to reduced feeding efficiency and growth rates, and even mortality in these herbivores.

 

On the other hand, in tomato plants affected by Tuta absoluta No changes were found in the morphology of the mouthparts, but damage to the gut cells of caterpillars fed on leaves that received Si, which was attributed to the synthesis of toxic substances associated with the presence of Si, which resulted in decreased feed efficiency and increased mortality (Santos et al. 2015).

The use of Si in rice plants increased the activity of some plant defense enzymes, achieving less defoliation of the plants caused by the caterpillar Cnaphalocrocis medinalis. (Han et al., 2016). In a trial on cucumber it was observed that in plants where Si had been applied there was an increase in the synthesis of defensive volatile chemical compounds during the attack of the cucumber beetle, Diabrotica balteata (Callis-Duehl et al. 2017).

Recently, Hall et al. (2019) indicate that the efficiency of Si against insect attacks is due to the presence of the element stimulates increases in the synthesis of jasmonic acid in plants, which is an endogenous phytohormone that regulates plant growth but can also be produced by them after damage caused by an insect, resulting in increased production of resistance compounds.

 

3. 2. 3. VIRUS

 

The information in the literature is still very scarce in the case of the effect of Si in mitigating or preventing the harmful effects on the plant caused by viral pathogens when compared with the information available for other pathogenic agents (Sakr, 2016).

 

4. USE OF SILICON IN AGRICULTURE 

 

In modern agriculture, Si has been shown to be beneficial for a range of species. The element's positive influence on crops has been known since Justius Von Leibigh published a paper in 1840 on the benefits of Si from the perspective of plant mineral nutrition. Since then, several other methods have been developed. Laboratory, greenhouse and field trials have shown the benefits of Si fertilization on productivity, development and tolerance to various stresses. in herbaceous crops such as rice, corn, wheat, barley, sugarcane, pumpkin, and in woody crops such as citrus, avocado, chestnut, plum, mango, apple, peach, pistachio and grapevine, among others (Bertling et al. 2009; Carneiro-Carvalho et al. 2020; Ferreira et al. 2013; Ramírez-Godoy et al. 2018; Ghoreishi et al. 2019; Valdebenito et al. 2018; Kadlecová et al. 2020; Cetinkaya and Kulak, 2019; Schabi et al. 2020).

Woody crops are characterized by having lignified tissue that provides rigidity to the cell wall, slow growth, and a long vegetative cycle. They constitute a group of great economic interest, including forest and fruit species (Gardner et al. 2017). In the case of fruit trees, characterized as non-Si accumulators, the presence of the element in them is very low. However, It can actively participate in these woody species by reducing different types of stress of abiotic and biotic nature., especially in organic farming where Si fertilization can pave the way for minimal use of synthetic fertilizers and pesticides (Patil et al. 2017).

 

There are a number of solid and liquid sources of Si on the market, which are used as soil amendments or fertilizers, such as diatomite, calcium silicate, sodium metasilicate, potassium silicate, magnesium silicate, orthosilicic acid, hydrated silicon dioxide and calcium metasilicate (Ferreira, 2017). The most commonly used compound to provide Si to crops are silicates.Chemically, silicates are salts of silicic acid, formed from the two common elements: Si and O, and they also have accessory elements that give them different characteristics (Demattê et al. 2011). Silicates bound to a cation have greater solubility and availability of Si, with silicates with monovalent cations (sodium silicate and potassium silicate) being the most soluble sources (Korndörfer and Pereira, 2013).

 

5. RECOMMENDATION 

En Cultivator We have a product formulated based on silicon, CultisilK. It is a Potassium solution (10%) with silicon (22,5%) and amino acids (2,5%)As a source of potassium and silicon, Improves plant growth and strengthens its resistance to environmental factors, enhancing self-defenseSilicon is a structural element that reinforces the cell wall, strengthening the physical support of the plant and protecting it from attack by external agents. It also has synergies with calcium, magnesium and potassium, improving its absorption and transport in the plantIt is especially indicated for preventing lodging in cereals, fungal diseases in all types of plants, attacks by sucking insects, and general improvement of mechanical capacities to withstand wind, torrential rains, and other types of physical and chemical stress (salinity and water stress, among others).

Our Technical Department recommends your Application preventively before moments susceptible to attack by pathogens or prior to predictable situations of abiotic stress, repeating the treatments 2 or 3 times during these critical periods.

To request references, send an email to info@cultifort.com