Si Fertilization Research Articles

Silicon fertilization influences microbial assemblages in rice roots and decreases arsenic concentration in grain: A five-season in-situ remediation field study

Microbial mechanism of in-situ remediation of arsenic (As) in As-contaminated paddy fields by silicon (Si) fertilization has been rarely reported, especially under continuous rice cultivation and Si applications. In this study, two Si fertilizers were applied for three phases in five consecutive rice seasons to investigate the long-lasting impacts on in-situ remediation of As, and the underpinning microbial mechanism of root-associated compartments (bulk soil, rhizosphere and endosphere) was explored using the last double-cropping rice. Repeated application of Si fertilizers as base manure had a long-lasting effect on reducing As concentrations in rice grains. Application of Si fertilizer at an adequate amount resulted in an extended in-situ remediation effect from endosphere to rhizosphere. The microbial diversity and richness in rhizosphere soil and endosphere were significantly impacted by Si fertilization, the effects depending on application doses and prolonged seasons. Si fertilization can immobilize As in the root or rhizosphere, and Fe concentrations and the As- and Fe-transforming microorganisms (i.e. Geobacteraceae) are the determinants of As uptake in rice. We recommend more extensive supplementation of Si fertilizer at a higher rate to decrease grain As concentration for in-situ remediation. This study sheds light on the microbial-mediated mechanism underlying Si fertilization effect on decreased As uptake in paddy fields.

Silicon Alleviates the Disease Severity of Sclerotinia Stem Rot in Rapeseed.

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a devastating disease in rapeseed. The objective of this study was to investigate the role and the mechanism of silicon (Si) in alleviating the disease severity of S. sclerotiorum in rapeseed. In the absorption assays, the rapeseed that absorbed 10 mM of K2SiO3 exhibited an 86% decrease in lesion size on infected leaves as compared with controls. In the spray assay, the lesion length on rapeseed stems was reduced by 30.5–32.9% with the use of 100 mM of a foliar Si fertilizer as compared with controls. In the pot assay, the lesion length on rapeseed stems was reduced by 34.9–38.3% when using the Si fertilizer as basal fertilizer. In the field assay, both the disease incidence and disease index of sclerotinia stem rot were significantly reduced with the usage of a solid Si fertilizer, Si foliar fertilizer, and the application of both, without negative affection on the main agronomic traits and seed quality of rapeseed. The transcriptome sequencing, quantitative reverse transcription PCR (qRT-PCR), and biochemical assays between K2SO4- and K2SiO3- treated rapeseed leaves revealed that Si promoted the biosynthesis of defense-related substances and enhanced the antioxidation and detoxification abilities of rapeseed after infection. Thus, this study concluded that Si can alleviate the disease severity of S. sclerotiorum in rapeseeds, partially due to the induced defense responses.

SPAD index and leaf pigments in cauliflower in different water conditions and silicon fertilization

The measurement of leaf pigments using non-destructive methods can be influenced by water management conditions and the use of nutrients in cauliflower, not showing adequate correlations with chlorophyll contents. The objective of this study was to evaluate the correlation between the SPAD index and the pigment content in cauliflower leaves managed with different water conditions and the application of silicon (Si). The cultivation was carried out in a protected environment in the city of Maringá, Paraná State from October 2019 to March 2020. It was adopted a randomized block design, with treatments in a 3 x 4 factorial scheme, with three levels of water recharge (40; 70 and 100% of crop evapotranspiration (ETc)) and four doses of Si (0; 50; 100 and 150 kg ha-1), with four replications. Once plants showed developed inflorescence, the SPAD index was determined in the field and the levels of chlorophyll a, chlorophyll b, and carotenoids in the laboratory using leaves from the upper third. The correlation between water recharge and Si fertilization on the SPAD index was determined. The proportion of carotenoids in relation to total pigments was compared under different conditions. Correlation analysis was performed considering silicon fertilization, water recharge, leaf pigments, and the SPAD index. Silicon fertilization reduced the levels of carotenoids in addition to being related to chlorophyll a (100% of ETc) and chlorophyll b (70% of ETc). The correlation of the SPAD index with pigments is variable with the water condition of the crop, in a condition without water deficit, it is related to chlorophyll a and in a condition of 70% replacement of ETc, it is correlated with chlorophyll b.

Effects of Silicon and Silicon-Based Nanoparticles on Rhizosphere Microbiome, Plant Stress and Growth.

Simple SummaryAbiotic and biotic stresses are a major challenge for agricultural production. To deal with stressed conditions, many techniques, including the use of nanoparticles (NPs), could be considered to mitigate the adversities mediated by these stresses. The application of silicon (Si) and Si-NPs has emerged as a common agronomic technique as it is regarded as a sustainable option. Because of their innumerable benefits, the usage of Si and Si-NPs has attracted a great deal of interest. As a result, their application has been found to minimize the detrimental effects of various stressors by modifying morpho-physiological indices in plants and rhizospheric microbiome characteristics.Silicon (Si) is considered a non-essential element similar to cadmium, arsenic, lead, etc., for plants, yet Si is beneficial to plant growth, so it is also referred to as a quasi-essential element (similar to aluminum, cobalt, sodium and selenium). An element is considered quasi-essential if it is not required by plants but its absence results in significant negative consequences or anomalies in plant growth, reproduction and development. Si is reported to reduce the negative impacts of different stresses in plants. The significant accumulation of Si on the plant tissue surface is primarily responsible for these positive influences in plants, such as increasing antioxidant activity while reducing soil pollutant absorption. Because of these advantageous properties, the application of Si-based nanoparticles (Si-NPs) in agricultural and food production has received a great deal of interest. Furthermore, conventional Si fertilizers are reported to have low bioavailability; therefore, the development and implementation of nano-Si fertilizers with high bioavailability could be crucial for viable agricultural production. Thus, in this context, the objectives of this review are to summarize the effects of both Si and Si-NPs on soil microbes, soil properties, plant growth and various plant pathogens and diseases. Si-NPs and Si are reported to change the microbial colonies and biomass, could influence rhizospheric microbes and biomass content and are able to improve soil fertility.

Effect of Combined Application of Foliar Sprays of Orthosilicic Acid (OSA) with Basal NPK Fertilizer on Growth and Yield of Rice (Oryza sativa L.)

Benefits of silicon to plant growth and yield in higher plants has been explored recently. This study was conducted to assess effects of application of foliar application of stabilized Orthosilicic Acid (OSA) with NPK fertilizer on growth and yield of rice. The study was conducted in Ntende site at Rwagitima marshland, Gatsibo district in the Eastern province of Rwanda. The field experiment was laid in randomized complete block design with three replications across two cropping seasons in 2019 and 2020. Two recommended doses of fertilizer (RDF); 100 % RDF (200 kgha− 1 NPK and 100 kgha− 1 Urea) and 75 % RDF (150 kgha− 1 NPK and 75 kgha− 1 Urea) were used in combination with different doses of stabilized orthosilicic acid (OSA), a commercial formulation is named as Silixol OSA (referred as OSA in the text). The Si fertilizer was applied in at panicle initiation and grain filling stages, at three different doses (2 ml/l, 3ml/l and 4 ml/l). Combined application of Silixol OSA with RDF produced better growth attributes (plant height, number of tillers, root length, flag leaf length and width) compared to that of RDF only. Similarly, OSA application showed higher yield components, number of panicles, panicle weight, grain weight per panicle and 1000-grain weight. Highest yield of 5.81 t/ha which equates to 24 % increase was obtained when 100 % RDF + 4ml/l OSA was applied. Interestingly, when OSA was used at 4ml/l dose, with 75 % RDF, it attributed to significant increase in yield. Rice fertilization with OSA helps to stimulate plant growth, yield attributes and yield. Therefore, potential of Si could further be explored among rice farmers in Rwanda. Further saving of 25 % of fertilizer dose would be a good economic benefit to farmers as well as government of Rwanda. Lesser use of fertilizers would also reduce the risk of degradation of environment following the application of OSA fertilizer.

Two-year and multi-site field trials to evaluate soil amendments for controlling cadmium accumulation in rice grain

Representing the staple crop for half of the world population, rice can accumulate high levels of cadmium (Cd) in its grain, posing concerns on food safety. Different soil amendments have been proposed to decrease Cd accumulation in rice grain by either decreasing soil Cd availability, introducing competitive ions on Cd uptake, or down-regulating the expression of transporters for Cd uptake. However, the effectiveness of soil amendments applied alone or in combinations needs to be tested under field conditions. Here, we present results of field trials with two rice cultivars differing in Cd accumulation grown at three field sites in southern China in two years, to investigate the effects of two Mn-containing soil amendments (MnO2, Mn-loaded biochar (MB)), Si fertilizer (Si), limestone, and K2SO4, as well as interactions among MnO2, Si, and limestone on decreasing Cd accumulation in rice grain. We found that single applications of MnO2 or MB to acidic soils low in Mn decreased grain Cd concentrations by 44–53 % or 78–82 %, respectively, over two years without decrease in performance. These effects were comparable to or greater than those induced by limestone liming alone (45–62 %). Strong interactions between MnO2 and limestone resulting from their influence on soil extractable Cd and Mn led to non-additive effects on lowering grain Cd. MB addition minimized grain Cd concentrations, primarily by increasing extractable and dissolved Mn concentrations, but also by decreasing Cd extractability in soil. In comparison, Si and K2SO4 amendments affected grain Cd levels only weakly. We conclude that the amendments that decrease labile Cd and increase labile Mn in soils are most effective at reducing Cd accumulation in rice grain, thus contributing to food safety.

Nutritional and Structural Role of Silicon in Attenuating Aluminum Toxicity in Sugarcane Plants

We investigated the interactive role of Si-mediated attenuation to aluminum (Al) toxicity in two sugarcane cultivars (‘CTC9002’ and ‘CTC9003’) grown in hydroponic conditions. Two pot experiments were distributed in randomized blocks in a factorial design (4 × 2) with four replications. The treatments consisted of 0, 10, 15, and 20 mg L−1 Al (as aluminum sulfate [Al2 (SO4)3·18H2O)], which were combined with the absence and presence of Si [(2.0 mmol L−1 as potassium silicate (K2SiO3)]. Both sugarcane cultivars (‘CTC9002’ and ‘CTC9003’) were affected by Al toxicity (above 10 mg L−1), resulting in nutritional disorders and decreasing plant growth, which were drastically reversed by Si addition in the growth medium. Si supplementation decrease Al concentration and translocation to the shoots of both cultivars when Al and Si were simultaneously supplied in the growth medium. We demonstrated that in shoots of both sugarcane seedlings, Si concentration are positively related to the lignin concentrations (ranging from 12.0% to 41% in cv. ‘CTC9002’ and 12% to 47% in cv. ‘CTC9003’). In addition, Si fertilization enhanced mineral nutrition and use efficiency of macros- and micronutrients, irrespective of the cultivar. Therefore, the use of cultivar ‘CTC9003’ under Si fertilization is more recommended to cope with the adverse effect caused by Al stress. The findings of this study suggest that Si fertilization in sugarcane seedlings is an economic and viable strategy strongly recommended to cope with the adverse effect caused by Al toxicity at concentrations less than 20 mg L−1, which lead to increase the shoot biomass production.

Effect on soil water availability, rather than silicon uptake by plants, explains the beneficial effect of silicon on rice during drought

Various studies showed a decrease of drought stress specific parameters of plants after silicon (Si) fertilization. But all studies differed in soil Si concentration between the control and Si treatments. As amorphous silica (ASi) was recently found to cause a strong increase of water holding capacity and plant available water in soils, a combined effect of soil moisture and plant response due to Si addition was assumed. In this study, the influence of the soil Si content was excluded by using the same Si enriched soil for treatments of two rice lines, lsi1 mutant defective in Si uptake and its wild-type rice. Most plant parameters, such as nutrient contents, biomass, specific leaf area, specific root length, leaf water content and C allocation did not differ significantly between the genotypes neither under flooded conditions, nor under drought conditions. Only photosynthesis and stomatal conductance were slightly higher for the wild type in both drought and flooded treatments. Overall, our data showed that Si accumulation within the plant tissues has only a minor effect on plant performance under drought stress. Hence, existing studies should be reinterpreted in light of the fact that Si additions may increase soil water availability.

Effect of pyrolysis temperature on Si release of alkali-enhanced Si-rich biochar and plant response

Recent studies have shown that silicon (Si) dissolution from biochar may be influenced by the pyrolysis temperature. In addition, the enhancement of biochar by treatment with alkali has been proposed to produce a Si source that can be used for environmentally friendly plant disease control. In this study, biochars from rice straw and rice husk pretreated with KOH, CaO and K2CO3 and then pyrolyzed at 350, 450 and 550 °C were prepared to evaluate the effects of pyrolysis temperature on Si release and plant uptake from alkali-enhanced Si-rich biochar. Extractable Si and dissolution Si from the prepared biochars were assessed by different short-term chemical methods and long-term (30-day) release in dilute acid and neutral salt solutions, respectively, along with a rice potting experiment in greenhouse. For both rice straw- and husk-derived alkali-enhanced biochars (RS-10KB and HS-10K2B, respectively), increasing the pyrolysis temperature from 350 to 550 °C generally had the highest extractable Si and increased Si content extracted by 5-day sodium carbonate and ammonium nitrate (5dSCAN) designated for fertilizer Si by 61–142%, whereas non-enhanced biochars had more extractable Si at 350 °C. The alkali-enhanced biochars produced at 550 °C pyrolysis temperature also released 82–172% and 27–79% more Si than that of 350 °C produced biochar in unbuffered weak acid and neutral salt solutions, respectively, over 30 days. In addition, alkali-enhanced biochars, especially that derived from rice husk at 550 °C facilitated 6–21% greater Si uptake by rice and 44–101% higher rice grain yields than lower temperature biochars, non-enhanced biochars, or conventional Si fertilizers (wollastonite and silicate calcium slag). Overall, this study demonstrated that 550 °C is more efficient than lower pyrolysis temperature for preparing alkali-enhanced biochar to improve Si release for plant growth.

Thermal Preparation and Application of a Novel Silicon Fertilizer Using Talc and Calcium Carbonate as Starting Materials

The deficiency of available silicon (Si) incurred by year-round agricultural and horticultural practices highlights the significance of Si fertilization for soil replenishment. This study focuses on a novel and economical route for the synthesis of Si fertilizer via the calcination method using talc and calcium carbonate (CaCO3) as starting materials. The molar ratio of talc to CaCO3 of 1:2.0, calcination temperature of 1150 °C and calcination time of 120 min were identified as the optimal conditions to maximize the available Si content of the prepared Si fertilizer. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) characterizations elucidate the principles of the calcination temperature-dependent microstructure evolution of Si fertilizers, and the akermanite Ca2Mg(Si2O7) and merwinite Ca3Mg(SiO4)2 were identified as the primary silicates products. The results of release and solubility experiments suggest the content of available metallic element and slow-release property of the Si fertilizer obtained at the optimum preparation condition (Si-OPC). The surface morphology and properties of Si-OPC were illuminated by the results of scanning electron microscope (SEM), surface area and nitrogen adsorption analysis. The acceleration action of CaCO3 in the decomposition process of talc was demonstrated by the thermogravimetry-differential scanning calorimetry (TG-DSC) test. The pot experiment corroborates that 5 g kg−1 soil Si-OPC application sufficed to facilitate the pakchoi growth by providing nutrient elements. This evidence indicates the prepared Si fertilizer as a promising candidate for Si-deficient soil replenishment.

Silicon fertilization increases gas-exchange and biomass by silicophytolith deposition in the leaves of contrasting drought-tolerant sugarcane cultivars under well-watered conditions

PurposeSilicon (Si) fertilization provides benefits to sugarcane. However, information remain scarce about the relationship between Si fertilization, gas exchange responses, biomass and silicophytolith accumulation in contrasting drought tolerant sugarcane cultivars under well-watered conditionsMethodsSugarcane cultivars (drought-tolerant and drought-sensitive) were grown in pots containing soil with low available Si and were treated (at rates equivalent to 0, 250, 500, 750, and 1000 kg ha−1 Si) with Si as silicate. The silicophytolith contents, morphotype descriptions, Si concentrations and gas exchange were evaluated in the top visible dewlap leaves. Stalk length and stalk biomass were also evaluated.ResultsThe silicophytolith, Si contents, net CO2 assimilation rate (A), plant transpiration (E), stomatal conductance (gs) and electron transport rate (ETR) of leaves and fresh biomass and length of stalks increased linearly as functions of the Si application rate, independent of cultivar. RB86-7515 showed the highest stalk length, fresh stalk and green leaf biomass, relative water content, and water potential, while RB85-5536 showed superior values for A, E, gs, and ETR.ConclusionsSi fertilization improved photosynthesis, transpiration, stalk length, and stalk biomass production in sugarcane. The highest silicophytolith content was reflected in a diversity of silicified cells, which may favor a higher photosynthesis and biomass. The increase of silicification in stomata complexes and trichomes with Si may be associated to a higher Si availability and transpiration. Contrasting drought-tolerant cultivars showed similar silicification and gas exchange responses with Si. Considering these benefits, Si should be included in the fertilization program of sugarcane.

Methane fluxes but not respiratory carbon dioxide fluxes altered under Si amendment during drying – rewetting cycles in fen peat mesocosms

Peatlands are globally important sinks and sources for greenhouse gasses. Their carbon (C) balances are dependent on input of biomass, its quality and decomposition. Silicon (Si) is known to influence the C quality, especially of graminoids, and it influences decomposition under oxic conditions. Drying – rewetting events (D/W), which may influence C mineralization and change nutrient availability, have been predicted to increase in frequency. This raises the question if effects of Si on decomposition are modified by such D/W events.To elucidate this question, we conducted a study with mesocosms extracted from a fen peatland.We hypothesized, that (I, II) there would be higher gas and solute concentrations after Si addition compared to the control after D/W. Further we expected (III) that higher respiratory fluxes of CO2 and CH4 would occur after Si addition and D/W and that (IV) there would be a higher gross primary production (GPP) under Si addition due to more viable biomass that is less prone to drought effects. Finally we hypothesized that (V) the chemical composition of Carex rostrata Stokes leaves grown under Si fertilization after a D/W cycle would be less recalcitrant compared to of C. rostrata leaves from the controls. To test these hypotheses, a control and a Si treatment group of mesocosms were subjected to a controlled D/W cycle. We measured soil gas (DIC and CH4), and solute concentrations (P, Si, Fe and TOC) and gas fluxes of CO2 and CH4. Furthermore, we characterized the graminoid biomass for major element contents and by infrared spectroscopy (FTIR) for organic matter quality.Higher CH4 fluxes were observed in the Si fertilized mesocosms. There was no difference between the treatments in the ER CO2 fluxes, whereas the NEE and GPP fluxes indicated higher CO2 uptake in the Si treated mesocosms. Solute concentrations showed no differences, neither for dissolved gasses , nor for solutes. C. rostrata leaves had lower shares of lignin, waxes, fats, and phenols in plants from the Si fertilized mesocosms.We concluded, that during D/W, plants from Si fertilized mesocosms accumulated more Si than plants from the control mesocosms. These plants were more viable, produced potentially more exudates and had more readily decomposable litter than controls, due to their lower share in recalcitrant moieties. This may have stimulated CH4 production and emission of CH4 from the soil into the atmosphere through abundant aerenchyma roots, bypassing oxic, methanotrophic peat layers.

Responses of microbial community and soil enzyme to heavy metal passivators in cadmium contaminated paddy soils: An in situ field experiment

Heavy metal passivators could reduce the transfer of heavy metal ions from soil to crops and exhibit great potential in safe cropping in heavy metal contaminated agricultural soils. However, the effects of heavy metal passivators on microbial diversity and microorganisms-based biogeochemical processes in agricultural soil are poorly explored. In this study, the effects of three heavy metal passivators, viz. lime, silicon (Si) fertilizer, and gypsum, on the structure and function of microorganisms in cadmium (Cd) contaminated paddy soils were investigated through activity of soil enzyme, microbial abundance and community structure by an in situ paddy field plot experiment. Our results showed that lime application changed the activity of phosphatase and urease through increasing bio-available phosphorus (AP) content in soil and soil pH, respectively. Lime application increased abundance and richness of the prokaryotic microbes in paddy soil, while gypsum application increased evenness of the eukaryotic microbes. Si fertilizer application resulted in the increase of evenness of both prokaryotic and eukaryotic microbes. The results presented in this study suggest that application of heavy metal passivator lime, Si fertilizer, and gypsum could improve microbial diversity and function in Cd contaminated paddy soil.

How silicon fertilizer improves nitrogen and phosphorus nutrient availability in paddy soil?

In order to reveal the mechanism of silicon (Si) fertilizer in improving nitrogen (N) and phosphorus (P) nutrient availability in paddy soil, we designed a series of soil culture experiments by combining application of varying Si fertilizer concentrations with fixed N and P fertilizer concentrations. Following the recommendations of fertilizer manufacturers and local farmers, we applied Si in concentrations of 0, 5.2, 10.4, 15.6, and 20.8 μg/kg. At each concentration of added Si, the availability of soil N and P nutrients, soil microbial activity, numbers of ammonia-oxidizing bacteria and P-decomposing bacteria which means that the organic P is decomposed into inorganic nutrients which can be absorbed and utilized by plants, and urease and phosphatase activity first increased, and then decreased, as Si was added to the soil. These indicators reached their highest levels with a Si application rate of 15.6 μg/kg, showing values respectively 19.78%, 105.09%, 8.34%, 73.12%, 130.36%, 28.12%, and 20.15% higher than those of the controls. Appropriate Si application (10.4 to 15.6 µg/kg) could significantly increase the richness of the soil microbial community involved in cycling of N and P nutrients in the soil. When the Si application rate was 15.6 μg/kg, parameters for characterizing microbial abundance such as sequence numbers, operational taxonomic unit (OTU) number, and correlation indices of microbial community richness such as Chao1 index, the adaptive coherence estimator (ACE) index, Shannon index, and Simpson index all reached maximum values, with amounts increased by 14.46%, 10.01%, 23.80%, 30.54%, 0.18%, and 2.64%, respectively, compared with the control group. There is also a good correlation between N and P mineralization and addition of Si fertilizer. The correlation coefficients between the ratio of available P/total P (AP/TP) and the number of ammonia-oxidizing bacteria, AP/TP and acid phosphatase activity (AcPA), AP/TP and the Shannon index, the ratio of available N/total amount of N (AN/TN) and the number of ammoniated bacteria, and AN/TN and AcPA were 0.9290, 0.9508, 0.9202, 0.9140, and 0.9366, respectively. In summary, these results revealed that enhancement of soil microbial community structure diversity and soil microbial activity by appropriate application of Si is the key ecological mechanism by which application of Si fertilizer improves N and P nutrient availability.

The Effect of Plant Growth Compensation by Adding Silicon-Containing Fertilizer under Light Stress Conditions.

The effects of different spectral compositions of light-emitting diode (LED) sources and fertilizer containing biologically active silicon (Si) in the nutrient solution on morphological and physiological plant response were studied. Qualitative indicators and the productivity of plants of a red-leaved and a green-leaved lettuce were estimated. Lettuce was grown applying low-volume hydroponics in closed artificial agroecosystems. The positive effect of Si fertilizer used as a microadditive in the nutrient solution on the freshly harvested biomass was established on the thirtieth day of vegetation under LEDs. Increase in productivity of the red-leaved lettuce for freshly harvested biomass was 26.6%, while for the green-leaved lettuce no loss of dry matter was observed. However, being grown under sodium lamps, a negative impact of Si fertilizer on productivity of both types of plants was observed: the amount of harvested biomass decreased by 22.6% and 30.3% for the green- and red-leaved lettuces, respectively. The effect of using Si fertilizer dramatically changed during the total growing period: up to the fifteenth day of cultivation, a sharp inhibition of the growth of both types of lettuce was observed; then, by the thirtieth day of LED lighting, Si fertilizer showed a stress-protective effect and had a positive influence on the plants. However, by the period of ripening there was no effect of using the fertilizer. Therefore, we can conclude that the use of Si fertilizers is preferable only when LED irradiation is applied throughout the active plant growth period.

Silicate fertilization improves microbial functional potentials for stress tolerance in arsenic-enriched rice cropping systems

The host plant and its rhizosphere microbiome are similarly exposed to abiotic stresses under arsenic (As)-enriched cropping systems. Since silicon (Si) fertilization is effective in alleviating As-induced stresses in plants, and plant-microbe interactions are tightly coupled, we hypothesized that Si-fertilization would improve soil microbial functional potentials to environmental stress tolerance, which was not yet studied. With the help of high throughput metagenome, microarray and analyzing plant impacts on soil microbiome and the environment, we tested the hypothesis in two geographically different rice (i.e., Japonica and Indica) grown on As-enriched soils. Silicate fertilization in rice grown on As-enriched soils altered rhizosphere bacterial communities and increased several commensal microorganisms and their genetic potential to tolerate oxidative stress, osmotic stress, oxygen limitation, nitrogen and phosphate limitation, heat and cold shock, and radiation stress. The stress resistant microbial communities shifted with the changes in rhizosphere nutrient flows and cumulative plant impacts on the soil environment. The study highlights a thus-far unexplored behavior of Si-fertilization to improve microbial stress resilience under As-laden cropping systems and opens up a promising avenue to further study how commonalities in plant-microbe signaling in response to Si-fertilization alleviates As-induced stresses in agro-systems.

Elucidating the role of silicon in drought stress tolerance in plants

Predicted changes in climate, with more severe droughts and more extreme weather variability, are gaining considerable attention from stakeholders because of the already stressed and seriously challenging agricultural ecosystems of the contemporary world. One of the greatest challenges faced by these unique ecosystems due to climate change is drought stress, which affects plant growth, development and metabolic processes, thus reducing production, yield, and quality of crop plants. Plants counter this stress by employing complex mechanisms through a series of physiological, cellular, and molecular processes. Among the myriad of stress tolerance mechanisms, the positive effects of Si on water status of plants have been widely appreciated. Here, we review the potential of Si supplementation in alleviating drought stress and highlight the imported mechanisms involved in Si mediated reduction of drought stress in plants. Si fertilization not only enhances the photosynthetic pigments, growth, biomass, antioxidant enzymes, gene expression, osmolyte concentrations and nutrient uptake but also improves crop production, yield and grain quality during drought stress. In addition, it provides insights on important mechanisms involved in the modification of gas exchange attributes, gene modification, nutritional homeostasis, control synthesis of compatible solutes, osmotic adjustment and stimulation of phytohormone biosynthesis and antioxidant enzymes under drought stress. We also highlight knowledge gaps and future research prospects to understand Si mediated role in alleviating drought stress.

Efficiency and recovery index of silicon of a diatomaceous Earth-based fertilizer in two soil types grown with sugarcane and maize

Silicon (Si) plays an important role in crop yields and is known as a beneficial element for gramineous plants. Si sources used as fertilizers in Brazil are mainly industrial by-products and naturally occurring silica-rich minerals, such as calcium silicates. There is still relatively little information about Si fertilization in the country, especially in the potential of diatomaceous Earth (DE) as a Si fertilizer compared to other widely used sources. In this context, we aimed at assessing the efficiency of a DE-based fertilizer as Si supplier to plants of sugarcane and maize grown on two soil types. We used a calcium silicate source widely used in Brazil for comparison as a positive control. Results showed that the DE fertilizer application provided linear increase in the biomass of sugarcane and maize in the tested soils. The improvement in crop biomass correlated well with the Si accumulation in the shoots of the plants. Besides, DE fertilizer improved crop performance by increased N, P, K, and S concentrations in plants. When compared to the calcium silicate source, the DE fertilizer provided the same Si supplying potential for the tested plants and higher relative biomass yield.

Effect of organosilicone and mineral silicon fertilizers on chemical forms of cadmium and lead in soil and their accumulation in rice

Cadmium (Cd) and lead (Pb) pollution in soil and their accumulation in edible parts possess a worldwide eco-environmental and health risk, especially in developing countries. Recently, organosilicone fertilizer (OSiF) has been reported to reduce uptake of heavy metals, but the effectiveness has not been verified and its associated mechanisms are not fully understood. This work investigated whether and how OSiF and mineral silicon fertilizer (MSiF) affect mitigation of Cd and Pb stress in rice (Oryza sativa). Both soil incubation and pot experiments were conducted to assess the effect of OSiF and MSiF on bioavailability of Cd and Pb in soil and their accumulation in rice. Additionally, a hydroponic experiment was conducted to study whether Si in rice can alleviate Cd stress. We found that both Si fertilizers could increase soil pH, induce the transformation of the acid soluble and reducible fractions of Cd and Pb to the oxidizable and residual fractions in soil, decreasing their bioavailability and the uptake of Cd and Pb in rice. However, Si in OSiF was not phyto-available, but Si in MSiF was available since available Si in soil and Si in plant increased in MSiF treatments but not in OSiF treatments. Meanwhile, rice grain yields significantly increased and the Cd and Pb content of brown rice reduced in MSiF treatments but not in OSiF treatments. In addition, Si was found to be able to alleviate Cd stress by improving the antioxidant capacity of rice. These results suggested that the decreased Cd and Pb accumulation in OSiF-treated rice was due to Cd and Pb immobilization in soil simply with pH increase, but in MSiF-treated rice Cd and Pb immobilization in soil (ex planta effect) and Si-conferred inhibitory effect of root-to-shoot Cd and Pb transport (in planta effect) contribute to the lower accumulation in rice.

Effect of Silicic Acid Formulation (Silicon 0.8%) on Two Major Insect Pests of Tomato under Greenhouse Conditions

Tomato (Solanum lycopersicum L.) is an important vegetable crop in Iraq. This horticultural crop is attacked by several insect pest species. Among them, the whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and the tomato leaf miner Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) are the major threat of greenhouse tomatoes in Basrah province in southern Iraq. The management of these pests is heavily based on application of chemical pesticides. Vast application of pesticides caused harmful damage to the environment, human health and may increasing the risk of pest resistance on insect populations. One of the promising strategies which are compatible with organic farming is application of silicon for enhancing plant vigor and resistance to pest damage on various agricultural crops. Due to these facts, the experiments have been carried out at Basrah University to evaluate the effects of silicon (Si) fertilization on tomato plants for reducing damage of these two major pests. Treatments comprised two type of Si applications (Soil drench treatment and foliar spraying) with four Si concentrations (0, 0.5, 1 and 2%) of AB Yellow ® silicic acid formulation. The population density of B. tabaci and T. absoluta were studied weekly during the growth season. The results clearly demonstrated that Silicon applications significantly decreased the population of immature of both whiteflies and tomato leaf miner on tomato crop in the greenhouse; Si-Foliar spraying was more effective in reducing the population density of these key pests compared to Si- soil drench application.