سیلیسیم

In modern agriculture, silicon (Si) is considered as an essential and anti-stress nutrient for a number of plants, especially grasses and C4. There are arguments confirming that it is a quasi-essential element in relation to plants growth, development and reproduction. The present study aims to review a decade research in the field of chemistry and plant nutrition of the Si in soil and plants in the Department of Soil Science and Engineering, University of Tehran. The objectives of this article is to present the most important achievements of researches in the field of Si efficiency of maize and soybean cultivars and to investigate the effect of Si application on nutritional, physiological and morphological characteristics of different plants including wheat, corn, sorghum, etc. under stress conditions and also to assess the effect of Si application on immobilization of heavy metals in the soil. General conclusions of this study show that Si supplied by both chemical fertilizers and silicon-soluble bacteria, increase plant growth and yield via increasing the root system of plants, regulating the biosynthesis of plant hormones, stimulating the production of some antioxidant enzymes, increasing resistance to salinity/ drought/heavy metal toxicity stresses and also increasing plant accessibility to some nutrients such as phosphorus and nitrogen. In addition to these results, the fraction of Si in different soils have been studied and analyzed. It seems by focusing on researches done on this element in the "soil, plant and rhizosphere", it can be hopefull that these results will be more practical in the future of the country's agriculture.

Considering that most of the calcareous soils of Iran are deficient in one or more micronutrients, optimal nutrition of nutrients such as silicon under the influence of biological treatments can be highly effective in these conditions. Therefore, this study was conducted to investigate the effects of silicon and phosphate-soluble bacteria on the availability of micronutrients for wheat. We used a completely randomized design in three replications and treatments included 0, 150, 300, 600 mg/kg silicon from a source of silicic acid and three levels of bacteria (non-inoculation of bacteria, Bacillus and Pseudomonas). The study was conducted in the greenhouse of Soil and Water Research Institute. The results showed that the combined use of silicon and phosphate-solubilizing bacteria increased the uptake of manganese and iron compared to the control treatment. However, the antagonistic effect between nutrients reduced zinc uptake at higher levels of functional silicon. The effect of inoculation with Bacillus and Pseudomonas on the amount of zinc, manganese and iron uptake by wheat was superior to the control bacterium. On the other hand, application of silicon (600 mg silicon/kg soil with Pseudomonas bacteria) significantly increased the concentration of phosphorus in wheat to the optimum level. Since excessive use of phosphate fertilizer in calcareous soil reduces absorption of micro nutrients, the combined use of silicic acid and phosphate-soluble bacteria can be recommended as an effective method for increasing availability of micro nutrients in greenhouse conditions.

Photosynthetic parameters are the most sensitive process in the physiological metabolism of plants that are affected by irrigation regime and silicon fertilization. Thus, silicon is one of the effective elements in increasing the net rate of leaf photosynthesis, water use efficiency, stomatal conductance and intercellular carbon dioxide. Therefore, the aim of this study was to determine the effects of different levels of silicon sources and irrigation regimes on rice.

A pot experiment was conducted to investigate the effect of different levels of silicon sources and irrigation regimes on rice photosynthetic parameters at Sari Agricultural Sciences and Natural Resources University in 2018. The experiment was laid out in a split-factorial design with three replications. In this design, soil texture was considered as the main-plot factor, and irrigation regime and different levels of silicon sources as factorial-subplot factors. Factors included two Si doses of 60 and 120 mg Si Kg–1 as potassium silicate (Ps), sodium silicate (Ss), calcium silicate (Cs) and biochar (Bi) sources under two irrigation regimes (continuous flooding (W1) and periodic wetting-drying (W2)) in two soil series with different textures (Sandy-loam (S1) and Silty-clay (S2)). After plant growth, dry matter weight of straw and photosynthetic parameters such as relative leaf moisture content, transpiration intensity, stomata conductance, chlorophyll index and photosynthesis were measured in flag leaf at the flowering stage of rice.

The results showed that the highest leaf relative moisture content (63.80%), transpiration intensity (12.03 mmolm-2s-1), stomata conductance (384.79 mmolm-2s-1), chlorophyll content (55.00), photosynthesis rate (24.33 µmolm-2s-1) and dry matter weight of straw (33.3 gr/pot) were observed in plants treated with potassium silicate at a concentration of 120 mg Si Kg–1 of silty-clay soil under continuous flooding irrigation regime. The lowest dry matter weight of straw and photosynthetic parameters were observed in sandy-loam soil under periodic wetting-drying irrigation regime without using silicon fertilizer. Also, in sandy-loam soil, the leaf relative moisture content (58.95%), transpiration intensity (11.20 mmolm-2s-1), stomata conductance (340.32 mmolm-2s-1), chlorophyll content (51.80), photosynthesis rate (19.55 µmolm-2s-1) and dry matter weight of straw (18.6 gr/pot) was the highest in biochar treatment at a concentration of 120 mg Si Kg–1 under continuous flooding conditions. Also, a decrease in dry matter weight of straw and photosynthetic parameters was observed at the higher Si rates (120 mg Si Kg–1 compared to 60 mg Si Kg–1) in treatments of potassium silicate and sodium silicate in sandy-loam soil under periodic wetting-drying irrigation regime. This may be due to the inhibitory effect of high concentrations of silicon on photosynthetic function.

Although most of the photosynthetic parameters of plants and dry matter weight of starw in periodic wetting and drying irrigation regime were somewhat reduced compared to continuous flooding irrigation regime, application of different sources of silicon to both soil textures under both irrigation regimes improved relative leaf moisture content, transpiration rate, stomata conductance, chlorophyll content, photosynthesis rate and dry matter weight of straw were compared to treatments without silicon fertilizer application. This reflects the protective effect of silicon against low irrigation conditions. Therefore, in the scope of this experiment, it seems that the use of silicon to improve the photosynthetic parameters of rice plant and dry matter weight of straw under low-irrigation regime was satisfactory. But, the amount of use of this element is very important to maintain the balance of soil and plant properties.

Element efficiency is one of the most important characteristics of different plant cultivars for managing nutrition and fertilizer application in plants. This study was carried out to investigate the efficiency of silicon in different maize cultivars in a calcareous soil under greenhouse conditions. Treatments included five maize cultivars (single crosses 400 (ksc400), 410 (ksc410), 704 (ksc704), 705 (ksc705), 706 (ksc706)) and two silicon levels (0 and 100 mg silicon in 1 kg soil from potassium silicate source), which was performed in a factorial arrangement based on a completely randomized design. After eight weeks of vegetative period, plants harvested and factors such as shoot and root dry weight, leaf area, root volume and surface area and plant silicon uptake were measured. Efficiency element indices including adsorption and consumption efficiency of silicon and silicon efficiency of different cultivars were calculated. Among cultivars, ksc706 with 14.54 g yield, root weight of 6.7 g, leaf area of 173700 mm2 and root area of 185185 mm2 had the best results in terms of morphological characteristics and ksc410 cultivar with yield of 10.03 g, root weight of 5.25 g, leaf area of ​​2147900 mm2 and root area of ​​136284 mm2 showed the lowest desirable characteristics, compared to the control treatment. Yield increase of cultivars compared to the control treatment were: ksc400 (20.7%), ksc706 (17.8%), ksc410 (9.2%), ksc704 (8.9%) and ksc705 (4.8%). The highest silicon uptake efficiency was in ksc706 cultivar (85.7%) and the lowest in ksc704 (58.9%), and the highest silicon consumption efficiency was in ksc705 (12.52%) and the lowest in ksc400 (5.44%). With regard of increasing the area of root system in the treatment containing silicon compared to the control, and the effects of silicon on the uptake and transfer of more nutrients from the soil to the shoots, an increase in plant yield is evident. Accordingly, it is suggested to consider the development of planting the effective element plants with the aim of managing input consumption, soil fertility and sustainable agricultural goals.

Due to the importance of useful elements such as silicon in improving plant resistance to environmental and biological stresses, a factorial experiment was conducted in a completely randomized design in Hashtgerd city, hydroponic greenhouse No. 256. Experimental factors included temperature at 4°C (stress temperature) and 25°C (optimum growth temperature) and application of silicon fertilizer from source of silicic acid at five levels; 0, 500, 1000, 1500 and 2000 mg/kg with three replications, in total 30 pots. The measured traits included the activity of superoxide dismutase (SOD), catalase (CAT), antioxidant enzymes and the qualitative characteristics of aloe vera consist of Mannose, Glucomannan and Aloin concentrations and the plant growth characteristics including aloe vera gel and leaf weight, which were tested at 4°C as cold stress temperature and 25°C as the optimum growth temperature of the plant. The obtained results after applying cold stress showed that the effect of silicon fertilizer levels applied on (SOD) and (CAT) and Glucomannan and Mannose activities were significant at 1% level. It was also observed that the interaction of different concentrations of silicon fertilizer and temperature stress is significant at 1% level on all compounds. For vegetative and biochemical traits, the highest interaction was observed in treatment of 2000 mg/kg silicic asid fertilizer at 25°C. For antioxidants, the highest interaction was found in treatment of 2000 mg/kg silicic acid and stress temperature of 4°C. Therefore, the application of 2000 mg/kg pure silicon could have positive effects on the activity of antioxidant enzymes and vegetative traits at normal temperature and a more favorable effect on biochemical traits under temperature stress. Consequently, the silicium fertilizer can be applied as a useful and suitable element in ncreasing the quantity and quality of aloe vera plant.

One of the major environmental problems is heavy metal contamination of agricultural soils, especially in developing countries. The transfer of pollutants to human via plants endangers people helth in community. Lead (Pb) with higher shelf life toxicity in soil has a more devastating decrese on the biological activities in soils. Same application of silicon and biological treatments under heavy metal stresses rarely investigated before. In this study, it was tried to evaluate the feasibility of their simultaneous use on the properties of coriander.

This factorial experiment was conducted in a completely randomized design with four levels of Pb stress (0, 500, 1000 and 1500 mg.Kg), four levels of biological treatments (Without bacteria, strains 6, 19 bacteria and mycorrhizal fungi Glomus mosea) and three levels of silicon nano particles (0, 1.5 and 3 mM) on coriander plants. At the end of the experiment, traits including plant height, root and shoot weight, root length, leaf area, leaf dry weight, photosynthesis pigment (Chlorophyll a, b, and total, carotenoid), electro leakage, proline, and carbohydrate were measured in coriandrum sativum. Also, basal and induced respiratory and percentage of mychorizha colonization in soil were measured.

The results of this study showed that both mycorrhizae symbiosis and bacterial isolates inoculation were acceptable population even at high intensities, such that high amoun of Pb decresed population. Both application of Silicon nano particles and biological treatments showed desirable results in most of the studied traits. Morphological traits including fresh and dry weight of plant, leaf area, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid under both experimental treatments were partially offset by Pb treatment. The amount of electro lekage and proline under Pb stress, especially at high concentrations, was significantly increased, but the combination of silicon nano particles and biological treatments decreased this treatments significantly. Also, Pb increased the carbohydrate content of coriander plants, and the interesting thing was that it increased as a result of their joint application of silicon nano particles and biological treatments. It seems that the biological treatments in this study improved the growth of Coriandrum sativum under Pb contamination by affecting the root system and subsequently the effect on photosynthetic pigments.

In general, Pb, especially at high concentrations, caused significant deficiency in measured traits in Coriander. In this study, mycorrhizal and isolates 6 showed better results in most morphological and physiological conditions, although at lower concentrations of Pb in some isolates 19 also showed good results. Combining the microorganisem treatment with 3 mM silicon nanoparticles were better results in these traits. Simultaneous application of biological treatments and silicon in coriander is recommended for their individual application, although their mechanism has not been elucidated and needs further study. Key word: Silicon, PGPR, Morphological traits, basal respiration, Induced respiration.

One of the ways to improve the food security of a growing population of the world is to increase the amount of production per unit area. Some of the nutrient elements such as silicon not only increase nutrient use efficiency but also increment product quality. In this research, the effects of various sources of silicon included Potassium silicate, Calcium silicate, Humistar Si in two levels 200 and 400 mg/kg and Nano-silicon in two levels 50 and 100 mg/kg and Control treatment on morphophysiological responses of the herb of the stevia plant were examined. After three months, the plants were harvested and fresh and dry weight of shoot and root, height and diameter of the shoot, root volume and leaf area as morphophysiological indices of the plant, and leaf chlorophyll, the concentration of silicon, phosphorus, potassium in the shoots, and Glycosides in the stevia leaf, including Stevioside, Rebaudioside A and B were measured. The results showed the effects of silicon sources on the fresh and dry weight of shoot and root, height of shoot, root volume, stem diameter, leaf area and leaf chlorophyll index were significant. The treatments of calcium silicate-200, Nanosilicon-100, and Humistar silicon-200 yielded the highest fresh weight of the shoot compared to the control samples and Nanosilicon-100 led to an increase of 55, 64, and 35% of mentioned elements compared to the control treatment. The treatment of Humistar silicon-400 showed the highest amounts of Stevioside (5.23%), Rebaudioside A (0.67%). Considering the effectiveness of the use of silicon element on morpho-physiological and nutritional responses, and improving the quality of Stevioside and Rebaudioside sugars, it is recommended that along with the optimal use of nutrients, more attention should be paid to the role of this valuable element.

In order to investigation the use of bio-refining of silicon on cadmium and lead in spinach, in the pot experiment Qaemshahr Agriculture University in 2012 as a completely randomized design with four replications. Treatment include silicon (150mg/kg of Potassium silicon), Pb (100 mg/kg of chloride) ,Cd (100 mg/kg of chloride),silicon, silicon and control as used soil. The results showed that the use of silicon,Pb accumulation in shoot and roots decreased (34/4 ,65/2 percents) and also Cd accumulation in shoot and roots decreased (25/7 , 37/0 percents) respectively. The lowest shoot and root lengh was with Cd and Pb application, that less than in comparison with control(42/4 , 27/8 percents) respectively. At least bush fresh weight obtained with Pb and Cd separate application and silicon and Cd joint application . results this experiment can reception that silicon application caused the decrease Cd and Pb accumulation in shoot and root spinach plant.

Clay minerals have significant impacts on all physical, chemical and biological properties of soils. Weathering of clay minerals in soil could be affected by several factors such as redox status, dehydration, hydrolysis, dissolution, chelation (bond a metal ion with an organic capsule) and release of aluminum hydroxide into juicy clays structure through exchange position. Limited information is available about the influence of organic acids on dissolution of fibrous clay minerals especially in saline conditions. This study was carried out to identify the influence of studied parameters on release of magnesium, silicon and aluminum from sepiolite and palygorskite minerals.
A laboratory experiment was set up with a completely randomized design and factorial arrangement in three replications. Treatments included two types of mineral (sepiolite and palygorskite in size of 25-53 μm), two organic acids (0.01 M citric and oxalic) and a control and four salinity levels (0, 6, 12 and 24 dS/m). The sepiolite and palygorskite minerals were taken from a mine in Fariman city (northeastern Iran) and Tolsa Co. (Spain), respectively. Then their elemental composition and X-ray diffraction patterns were measured using Bruker Pioneer S4 and Bruker D8 machines, respectively. The concentrations of released elements were also measured by GBC atomic absorption spectrometer.
The results obtained from determination of elemental composition of sepiolite and palygorskite minerals showed that sepiolite has higher concentration of MgO than palygorskite which is compatible with those reported in literature. The presence of minor concentration of CaO in elemental composition of the both minerals suggests that both minerals have minor amounts of carbonates as the accompanying phase. This was further supported by the results of XRD analysis of the samples. The results also illustrated that the amount of released elements is highly affected by the type of organic acids, salinity and type of mineral. Among the organic acids, the amount of Mg and Al released from sepiolite and palygorskite in citric acid treated samples were greater than those from oxalic acid samples. However, oxalic acid was found to be more effective for extraction of Si from the minerals. With increasing salinity, the release of all elements was increased, however; in presence of organic acids the amount of released elements was reduced comparing with non-saline conditions. Moreover, the results illustrated that the ratio of released Si/ (Al) in sepiolite samples was higher than palygroskite.
The results of this study suggest that sepiolite is less stable than palygorskite and is much more weathered under the conditions studied.

In order to evaluate the effects of nitrogen and silicon (Si) plus biofertilizers on powdery mildew disease, physiological parameters and yield of wheat (Triticum aestivum L.) cv. N8019, a pot experiment was conducted in a factorial based randomized complete block design at Sari Agricultural Sciences and Natural Resources University during 2009. Treatments included biofertilizer in four levels (non-inoculation, Pseudomonas fluorescens + Bacillus subtilis, Azotobacter brasilense + Azospirillum lipoferum and Azospirillum + Pseudomona + Bacillus), three levels of nitrogen fertilizer (0, 35 and 70 kg nitrogen ha-1) and three levels of potassium silicate (0, 500 and 1000 mg/kg). Results showed that biofertilizers significantly increased both physiological parameters and grain yield of wheat compared to control. Maximum grain yield and leaf area (32.3 and 27.4 percent more than control) were recorded in those plants which received co-inoculation of Azotobacter + Azospirillum (Nitroxin). Furthermore, coinoculation of Pseudomonas with Bacillus (Barvar 2) plus either medium or maximum nitrogen fertilizer markedly improved chlorophyll a and chlorophyll b content. In the case of powdery mildew, the spraying of both 500 and 1000 ppm of silicon significantly reduced the amount of powdery mildew infection and percentage of infected plants compared to control.