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Agronomy

Silicon in agriculture

Mineral is used to control pests and increase the productivity and quality of agricultural products

Better known as a basic material in the electro-electronic industry, in the composition of integrated circuits or chips that are found in all electronic equipment such as computers and cell phones, silicon is now being used in Brazilian agriculture as well, for controlling pests, increasing productivity and improving the quality of agricultural products. One of the most recent studies in Brazil was carried out by a team of researchers coordinated by agronomist Carlos Alexandre Costa Crusciol, a professor from the Department of Plant Production at the School of Agronomic Sciences at the Paulista State University (Unesp), in Botucatu. In May of this year they finalized an experiment that showed the benefits of applying silicon to growing potatoes in the form of fertilizer, by incorporating it into the soil.

Results showed a 14.3% increase in the overall production of tubers of while sellable tuber production (potatoes that are good to eat) rose by 15.8%. Many of these positive results were provided by a 63% reduction in the number of “bedded” plants, i.e., those whose stalks and the leaves grow but are not erect; they lay flat against the soil causing a series of problems. The plant is deprived of photosynthesis in all its potential and becomes more easily susceptible to pathogens. Silicon strengthens the cell walls of the leaves and stems making the plants more erect and increasing the area exposed to the sun. “The reduction in the flattening of the stalks, which is helped by the application of silicon, may be related to better moisture conditions in the cells caused by osmotic adjustment (which yields better permeability), which have resulted in more turgid (dilated) cells that have greater mechanical resistance”, explains Crusciol.

Silicon, whose chemical element is Si, achieved great industrial status in the twentieth century thanks to its semiconductor properties and inexpensiveness. It is the second most abundant element on the planet after oxygen, but it is never found in isolation in nature; it always forms part of minerals like clay, feldspar, granite, quartz and sand. “It generally appears in the form of silicon dioxide (SiO2 – also known as silica) and silicates, which are compounds containing silicon, oxygen and metals”, says Crusciol. Silicon plays an important role in plant-environment relations, because it can help crops support climatic, soil and biological adversity better, the final result being an increase in production and a better quality product. The potato is one of the vegetable species most sensitive to lack of water, a phenomenon that occurs over large stretches of cultivated areas and may cause a reduction in production, depending on when it occurs and how long it lasts.

Water and drought
The availability of water in the soil is one of the environmental factors that most affects the development of growing crops. “More silicon in the soil seems to help the crop when there are water shortages”, says Crusciol. The accumulation of silica in the cell wall reduces the loss of water through transpiration and may be a factor in its adaptation to hydric stress.

Fertilization with silicon may also increase resistance to various fungus diseases and other pests. Greater absorption of this mineral provides mechanical protection for the plant’s epidermis, reducing infection by phytopathogens and increasing resistance to drought. “In the case of disease, numerous studies have shown that the increase in the plant’s resistance to the pathogen may be due to an alteration in its response to attack by the parasite, increasing the synthesis of toxins (phytoalexins) that may act as inhibiting or repellant substances, in addition to forming a mechanical barrier.” The research also evaluated the chemical attributes and concentration of silicon in the soil. Among the results obtained it was seen that the corrective agents that were applied raised the calcium and manganese concentrations in the soil.

The experiment with potatoes was carried out at the plant house of the School of Agronomic Sciences on the Unesp campus in Botucatu and included treatment in which silicon was both present and absent; the soil was corrected using dolomitic limestone and agri-silicon (calcium silicate and magnesium), and the same methodology was also used relative to water shortage. Agrisilicon is produced by Recmix, from Timóteo, in Minas Gerais. The source of this type of silicon for agriculture has its origins in the slurry from the blast furnaces of steel mills, mainly CSN and Usiminas. The material is collected by Recmix, an American company, recycled and transformed into several sub-products, such as agri-silicon.

Use of the product increased the performance of the potato plant, which did not occur with the plants treated only with lime. “The increase in production may also be related to the increase in the concentration of phosphorous in the soil and the reduction of flattening due to the application of silicate, which may have helped to increase the efficiency in intercepting sunlight and, as a consequence, helped the potatoes to fill out.”

Sugar cane and soybeans
The absorption of silicon in the soil occurs when it is found in the form of monosilicon acid, which comes from the decomposition of vegetable waste, the release of silicon from the oxides and hydroxides of iron and aluminum, the dissolving of crystalline and non-crystalline minerals, the addition of silicate fertilizers and irrigation water. Most of this mineral is incorporated into the cell wall, mainly in the cells of the epidermis.

The benefits of silicon in potatoes may also be extended to other crops. So Unesp’s School of Agronomic Sciences in Botucatu is carrying out studies with other crops, like soybeans, rice and sugarcane. In the case of gramineous plants such as sugarcane, silicon reduces transpiration and increases resistance to hot sunny days. In soybeans the application of silicon increases the formation of nodules and fixes nitrogen in the plant’s roots.

“The results we’ve had are encouraging and show that the application of this element is often of great benefit to other crops”, says Carlos Crusciol. One of the first crops to use silicon commercially was sugarcane. Two sugar and alcohol refineries in São Paulo are already spreading silicates on their plantations. One is the Colombo Mill in Ariranha, which spreads silicate on 35,000 ha, out of a total planted area of 60,000 ha. The other is the Guaíra Mill in the same town, which uses it on 10% of its 33,000 ha plantation. The two are in the Ribeirão Preto region. The advantage for sugarcane is mainly that it strengthens the entire plant, which becomes more resistant to insects and other pests. When they feed on the leaves, stems and roots, the insects feel discomfort in the mouth when they chew or bite off these parts, thanks to a mechanical effect due to the silicon, which makes the plant tougher”, explains Crusciol.

The benefits of silicon in sugarcane have already been very well studied in South Africa, where it is used for fighting the cane weevil (Eldana saccharina), an insect whose larvae develop inside the stems. In recent experiments carried out by researchers Malcolm Keeping and Olivia Kvedaras and others from the South African Sugar Research Institute (Sasri), it was shown that silicon makes cane stems more resistant to insect penetration. The use of calcium silicate prevented 20 to 30% of the loss of biomass and of the end product, sugar. “In Brazil there’s a sugarcane weevil (Diatraea saccharalis) that is one of the main pests of the crop and looks like E. saccharina”, says Crusciol. The use of silicon in agriculture is also studied and applied, particularly in Japan, in rice growing. In Florida, in the USA, silicon has already shown it can make sugar plantations (used for sugar production) more resistant to frosts.

The importance of silicon is well established for some crops but many of its functions have not yet been fully clarified by science, according to Professor Crusciol. “Silicon accumulates in the tissue of all plants, representing between 0.1% and 10% of the dry material, but as far as the growth and development of these plants are concerned it’s still not considered part of the group of essential or functional nutrients from the physiological point of view.” Just as silicon has been used as the main component in the production of glass and crystal, in solar cells and as the basis of the current electro-electronic industry, and given that it is also in the silicone used in medicine for implants, besides being used for making contact lenses and in the production of reinforced concrete and ceramics, there is no doubt that it will be increasingly used in agriculture in future.

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