A Case for Silicon Fertilization to Improve Crop Yields in Tropical Soils

Harnessing silicon nanoparticles and various forms of silicon for enhanced plant growth performance under salinity stress: application and mechanism

Agricultural production faces significant losses due to salinity, drought, pests, insects, and weeds, particularly in nutrient- and fertilizer-deficient soils. This review focuses on enhancing the productivity of crops grown in dry and saline environments. Silicon nanoparticles (Si NPs) and silicon compounds (SiO₂/SiO₃2⁻) have shown potential to improve crop yields while mitigating the effects of biotic and abiotic stresses. As an eco-friendly alternative to chemical fertilizers, herbicides, and pesticides, Si NPs stimulate germination, plant growth, biomass accumulation, and nutrient absorption due to their small size, large surface area, and ease of cellular penetration. These nanoparticles reduce salinity stress by modulating gene expression, leading to the activation of antioxidant enzymes such as SOD, CAT, and APX, which help combat reactive oxygen species (ROS). Treatment with low concentrations of nano-silica (100-300 mg/L) significantly enhances plants' tolerance to salinity. Si NPs, when combined with soluble polymeric materials and rhizobacteria, provide a sustainable impact due to their slow-release properties, offering prolonged protection against bacterial and viral infections under saline stress conditions.

Silicon-induced mitigation of salt stress in GF677 and GN15 rootstocks: insights into physiological, biochemical, and molecular mechanisms

Salinity is a common environmental stress that disrupts physiological and biochemical processes in plants, inhibiting growth. Silicon is a key element that enhances plant tolerance to such abiotic stresses. This study examined the effects of silicon supplementation on physiological, biochemical, and molecular responses of GF677 and GN15 rootstocks under NaCl-induced salinity stress. The experiment was conducted in a greenhouse using a factorial design with two rootstocks, three NaCl concentrations (0, 50, and 100 mM), and three silicon levels (0, 1, and 2 mM) in a randomized complete block design with three replicates. Salinity significantly reduced growth parameters, including shoot and root fresh and dry weights, RWC, and photosynthetic activity, with GN15 being more sensitive to salt stress than GF677. Silicon supplementation, especially at 2 mM, alleviated NaCl-induced damage, enhancing biomass retention and RWC under moderate and high NaCl levels. Additionally, silicon reduced electrolyte leakage, lipid peroxidation, and hydrogen peroxide accumulation, suggesting a protective role against oxidative stress. Biochemical analyses showed that silicon increased the accumulation of osmolytes such as proline, soluble sugars, glycine betaine, and total soluble protein, particularly in GF677. Silicon also boosted antioxidant enzyme activities, mitigating oxidative damage. In terms of mineral nutrition, silicon reduced Na+ and Cl- accumulation in leaves and roots, with the greatest reduction observed at 2 mM Si. Gene expression analysis indicated that NaCl stress upregulated key salt tolerance genes, including HKT1, AVP1, NHX1, and SOS1, with silicon application further enhancing their expression, particularly in GF677. The highest levels of gene expression were found in plants treated with both NaCl and 2 mM Si, suggesting that silicon improves salt tolerance by modulating gene expression. In conclusion, this study demonstrates the potential of silicon as an effective mitigator of NaCl stress in GF677 and GN15 rootstocks, particularly under moderate to high salinity conditions. Silicon supplementation enhances plant growth, osmotic regulation, reduces oxidative damage, and modulates gene expression for salt tolerance. Further research is needed to assess silicon's effectiveness under soil-based conditions and its applicability to other rootstocks and orchard environments. This study is the first to concurrently evaluate the physiological, biochemical, and molecular responses of GF677 and GN15 rootstocks to silicon application under salt stress conditions.

Unveiling a Hidden Synergy: Empowering Biofertilizers for Enhanced Plant Growth With Silicon in Stressed Agriculture

Food security is increasingly threatened by climate change and environmental pressures that hinder plant growth and development. Harnessing soil microorganisms, such as mycorrhizal fungi and plant growth-promoting bacteria, offers a promising approach to boost crop production. However, existing screening methods for these microorganisms often prove ineffective in real-world, stress-prone environments, limiting the efficacy of microbial biofertilizers. To address this challenge, this review proposes the integration of silicon-renowned for its stress-mitigating properties in plants-with biofertilizers. Silicon has been shown to work synergistically with plant growth-promoting microorganisms, enhancing plant resilience to environmental stress while improving colonization efficiency and plant-microbe interactions in stressful conditions. By combining silicon with biofertilizers to create silicon-enriched biofertilizers, this strategy has the potential to optimize microbial performance and fortify food security against global challenges. The review advocates for the co-application of silicon and microbial biofertilizers as a sustainable solution to boost plant resilience against environmental stressors, thereby contributing to agricultural sustainability.

The potential of Paraburkholderia species to enhance crop growth

Agrochemicals are the primary alternative for maintaining the high yields necessary to produce sufficient plant-based foods to supply the world population. In recent decades, one of the most extensively explored alternatives to replace agrochemicals and reduce their environmental impact has been the use of microorganism-based products to boost crop yields with less environmental impact. This review focuses on the results of studies that have demonstrated the potential of the genus Paraburkholderia to increase crop yields and be utilized in biofertilizers and biocontrol products. A literature search was performed electronically considering articles and books published until August 19, 2024. We identified 24 species of Paraburkholderia with the ability to improve crop yields after their inoculation by different methods on seeds, seedlings, plantlets, adult crops, or fruits. The effects of these bacteria have been tested under laboratory, greenhouse, or field conditions. These Paraburkholderia species mediate their positive impact on crop growth by direct and indirect plant growth-promoting mechanisms, which include improving nutrient uptake, stimulating growth by phytohormone production, regulation and stimulation of metabolic pathways, induction of abiotic stress tolerance, and disease control by direct pathogen inhibition or induction of systemic resistance in plants. The literature reviewed here supports the use of Paraburkholderia in bio-inputs under the actual panorama of climate change and the necessity to increase sustainable agriculture worldwide.

Fire effects on phytolith carbon sequestration

Phytolith have been recognized as an important soil bioavailable Si source for plants, as well as a sink of C and heavy metals in soils. Though the impacts of fire and heat on phytolith sequestration of some nutrients (phosphorus, potassium) and heavy metals have been addressed, little attention has been paid to fire's effects on phytolith carbon sequestration. In this study, the carbon and dissolved Si content of phytoliths extracted from 6 common grass species and their burned ashes, as well as phytoliths collected from different areas (burned, transitional, and unburned) of a pine forest, were compared to characterize the effects of open fire on phytolith carbon content, solubility, and carbon sequestration. The carbon content and Si dissolution of ashed phytoliths varied between plant species, and differed with phytoliths from modern plants. The topsoil phytoliths had increased carbon content, and generally decreased solubility across the gradient of unburned, transitional, and burned pine forest. We therefore conclude that open fire can cause changes in phytolith related carbon content and solubility, as well as its preservation in soils. This study provides new perspective on the effects of open fire on phytolith carbon sequestration and its estimation.

Enhancing crop disease management through integrating biocontrol bacteria and silicon fertilizers: Challenges and opportunities

To achieve sustainable disease management in agriculture, there's a growing interest in using beneficial microorganisms as alternatives to chemical pesticides. Bacteria, in particular, have been extensively studied as biological control agents, but their inconsistent performance and limited availability hinder broader adoption. Research continues to explore innovative biocontrol technologies, which can be enhanced by combining silicon (Si) with biocontrol plant growth-promoting rhizobacteria (PGPR). Both biocontrol PGPR and Si demonstrate effectiveness in reducing plant disease under stress conditions, potentially leading to synergistic effects when used together. This review examines the individual mechanisms by which biocontrol PGPR and Si fertilizers manage plant diseases, emphasizing their roles in enhancing plant defense and decreasing disease incidence. Various Si fertilizer sources allow for flexible application methods, suitable for different target diseases and plant species. However, challenges exist, such as inconsistent soil Si data, lack of standardized soil tests, and limited availability of Si fertilizers. Addressing these issues necessitates collaborative efforts to develop improved Si fertilizers and tailored application strategies for specific cropping systems. Additionally, exploring silicate-solubilizing biocontrol bacteria to enhance Si availability in soils introduces intriguing research avenues. Investigating these bacteria's diversity and mechanisms can optimize Si access for plants and bolster disease resistance. Overall, combining biocontrol PGPR and Si fertilizers or silicate-solubilizing biocontrol bacteria shows promise for sustainable agriculture, enhancing crop productivity while reducing reliance on chemical inputs and promoting environmental sustainability.

Photovoltaic cell-derived silicon fertilizer and its combined effect with silicate-dissolving bacteria Bacillus aryahattai on rice growing during the tillering stage

The widespread retirement of crystalline silicon solar cells in coming years poses a significant obstacle to sustainable development. Arable soils have experienced a gradual decline in available silicon levels due to intensive agricultural production. Therefore, it is feasible to repurpose recovered waste crystalline silicon cells below cell-reuse benchmark into agriculturally usable resources. This study investigates the impact of photovoltaic crystalline silicon-derived fertilizer (Si group), external silicate-dissolving bacteria (Bac group), and their combination (All group) on early rice nutrient uptake, growth development, and soil physical and chemical properties through a 45-day potting experiment. The combined addition of silicon fertilizer and bacteria significantly improved soil nitrification process (nitrate nitrogen NO3-N increased by 73.5%) and soil organic matter content by 16.2%. The increases in soil-available silicon (by 14.9%) and total potassium (by 19%) in the All and Si were significant. For rice growth, the addition of silicon fertilizer did not have a positive effect on dry matter accumulation and plant height possibly due to the Si threshold effect or K stress. However, the chlorophyll content of the Bac and All treatment groups was enhanced by 25% and 29%, respectively, suggesting the positive effect of bacteria on soil nitrogen utilization. The absorption of potassium by the plants was positively correlated with silicon, and the accumulation of silicon reduced the carbon content of the rice's aboveground parts by 7.3% to 9.0%. The study provides a feasible solution of recycling and reusing waste crystalline silicon in agricultural applications, and the results also have indicative significance for the sustainable rice production under non-stress environmental conditions.

Nano silica's role in regulating heavy metal uptake in Calendula officinalis

BACKGROUND

Soil contamination with heavy metals poses a significant threat to plant health and human well-being. This study explores the potential of nano silica as a solution for mitigating heavy metal uptake in Calendula officinalis.

RESULTS

Greenhouse experiments demonstrated, 1000 mg•kg- 1 nano silica caused a 6% increase in soil pH compared to the control treatment. Also in 1000 mg. kg- 1 nano silica, the concentrations of available Pb (lead), Zn (zinc), Cu (copper), Ni (nickel), and Cr (chromium) in soil decreased by 12%, 11%, 11.6%, 10%, and 9.5%, respectively, compared to the control. Nano silica application significantly reduces heavy metal accumulation in C. officinalis exposed to contaminated soil except Zn. In 1000 mg.kg- 1 nano silica shoots Zn 13.28% increased and roots Zn increased 13% compared to the control treatment. Applying nano silica leads to increase the amount of phosphorus (P) 25%, potassium (K) 26% uptake by plant, In 1000 mg.kg - 1 treatment the highest amount of urease enzyme activity was 2.5%, dehydrogenase enzyme activity, 23.6% and the highest level of alkaline phosphatase enzyme activity was 13.5% higher than the control treatment.

CONCLUSION

Nano silica, particularly at a concentration of 1000 mg.kg - 1, enhanced roots and shoots length, dry weight, and soil enzyme activity Moreover, it increased P and K concentrations in plant tissues while decreasing heavy metals uptake by plant.

Application of Silicon Influencing Grain Yield and Some Grain Quality Features in Thai Fragrant Rice

Silicon (Si) is a beneficial nutrient that has been shown to increase rice productivity and grain quality. Fragrant rice occupies the high end of the rice market with prices at twice to more than three times those of non-fragrant rice. Thus, this study evaluated the effects of increasing Si on the yield and quality of fragrant rice. Also measured were the content of proline and the expression of the genes associated with 2AP synthesis and Si transport. The fragrant rice varieties were found to differ markedly in the effect of Si on their quality, as measured by the grain 2AP concentration, while there were only slight differences in their yield response to Si. The varieties with low 2AP when the Si supply is limited are represented by either PTT1 or BNM4 with only slight increases in 2AP when Si was increased. Si affects the gene expression levels of the genes associated with 2AP synthesis, and the accumulation of 2AP in fragrant rice mainly occurred through the upregulation of Badh2, DAO, OAT, ProDH, and P5CS genes. The findings suggest that Si is a potential micronutrient that can be utilized for improving 2AP and grain yield in further aromatic rice breeding programs.

Yield, lodging, and water use efficiency of Tef [Eragrostis tef (zucc) Trotter] in response to carbonized rice husk application under variable moisture condition

Terminal drought and lodging are among the major yield-limiting factors for tef cultivation in the highly weathered soils of the Ethiopian highlands. Therefore, a study was conducted to assess the yield and lodging responses of tef to varying moisture depletion levels (MDL) and the application of carbonized rice husk (CRH). A two-year 4×4 factorial experiment with 20, 35, 55, and 75% MDL and 0, 291, 582, and 873 kg ha-1 of CRH was laid out in a split-plot design, with each treatment replicated four times. The pooled mean ANOVA showed leaf area index (LAI) and lodging index (LI) were not significantly influenced by the main and interaction effects of MDL and CRH (p > 0.05); however, individual year ANOVA showed that both LI and LAI were influenced by the interaction of MDL and CRH (p<0.05) in 2021 and 2022, respectively. The lowest LI (19.7%) was obtained from the application of 873 kg CRH ha-1, followed by 20.6% from 582 kg CRH ha-1 in 2022. A 20.7% LI reduction was recorded in 2022 compared to 2021. Tef plant height and number of tillers per plant were significantly affected by MDL at p<0.05 and p<0.01, respectively, but not by CRH and its interaction with MDL. The effect of MDL was significant on tef HI (p<0.01) but not on traits including grain yield, straw yield, and water use efficiency. In conclusion, the pooled mean analysis result showed that, though there was no significant difference in yield, tef irrigated at 55% MDL provided a maximum HI of 33.8%, which was 6.21% more than the control, and increased the level of lodging resistance with a LI of 31.9%, which was next to 75% MDL with 582 kg ha-1 CRH. The authors suggested that the research should further be verified across locations for wide application.

Exploring the potential: Can arsenic (As) resistant silicate-solubilizing bacteria manage the dual effects of silicon on As accumulation in rice?

Rice (Oryza sativa L.) cultivation in regions marked by elevated arsenic (As) concentrations poses significant health concerns due to As uptake by the plant and its subsequent entry into the human food chain. With rice serving as a staple crop for a substantial share of the global population, addressing this issue is critical for food security. In flooded paddy soils, where As availability is pronounced, innovative strategies to reduce As uptake and enhance agricultural sustainability are mandatory. Silicon (Si) and Si nanoparticles have emerged as potential candidates to mitigate As accumulation in rice. However, their effects on As uptake exhibit complexity, influenced by initial Si levels in the soil and the amount of Si introduced through fertilization. While low Si additions may inadvertently increase As uptake, higher Si concentrations may alleviate As uptake and toxicity. The interplay among existing Si and As availability, Si supplementation, and soil biogeochemistry collectively shapes the outcome. Adding water-soluble Si fertilizers (e.g., Na2SiO3 and K2SiO3) has demonstrated efficacy in mitigating As toxicity stress in rice. Nonetheless, the expense associated with these fertilizers underscores the necessity for low cost innovative solutions. Silicate-solubilizing bacteria (SSB) resilient to As hold promise by enhancing Si availability by accelerating mineral dissolution within the rhizosphere, thereby regulating the Si biogeochemical cycle in paddy soils. Promoting SSB could make cost-effective Si sources more soluble and, consequently, managing the intricate interplay of Si's dual effects on As accumulation in rice. This review paper offers a comprehensive exploration of Si's nuanced role in modulating As uptake by rice, emphasizing the potential synergy between As-resistant SSB and Si availability enhancement. By shedding light on this interplay, we aspire to shed light on an innovative attempt for reducing As accumulation in rice while advancing agricultural sustainability.

Silicon supply promotes differences in growth and C:N:P stoichiometry between bamboo and tree saplings

BACKGROUND

Si can be important for the growth, functioning, and stoichiometric regulation of nutrients for high-Si-accumulating bamboo. However, other trees do not actively take up dissolved silicic acid [Si(OH)4] from the soil, likely because they have fewer or no specific Si transporters in their roots. It is unclear what causes differential growth and C:N:P stoichiometry between bamboo and other trees across levels of Si supply.

RESULTS

Si supply increased the relative growth rate of height and basal diameter of bamboo saplings, likely by increasing its net photosynthetic rate and ratios of N:P. Moreover, a high concentration of Si supply decreased the ratio of C:Si in bamboo leaves due to a partial substitution of C with Si in organic compounds. We also found that there was a positive correlation between leaf Si concentration and its transpiration rate in tree saplings.

CONCLUSIONS

We demonstrated that Si supply can decrease the ratio of C:Si in bamboo leaves and increase the ratio of N:P without altering nutrient status or the N:P ratio of tree saplings. Our findings provide experimental data to assess the different responses between bamboo and other trees in terms of growth, photosynthesis, and C:N:P stoichiometry. These results have implications for assessing the growth and competition between high-Si-accumulating bamboo and other plants when Si availability is altered in ecosystems during bamboo expansion.

Chemopriming for induction of disease resistance against pathogens in rice

Rice is an important grain crop of Asian population. Different fungal, bacterial and viral pathogens cause large reduction in rice grain production. Use of chemical pesticides, to provide protection against pathogens, has become incomplete due to pathogens resistance and is cause of environmental concerns. Therefore, induction of resistance in rice against pathogens via biopriming and chemopriming with safe and novel agents has emerged on a global level as ecofriendly alternatives that provide protection against broad spectrum of rice pathogens without any significant yield penalty. In the past three decades, a number of chemicals such as silicon, salicylic acid, vitamins, plant extract, phytohormones, nutrients etc. have been used to induce defense against bacterial, fungal and viral rice pathogens. From the detailed analysis of abiotic agents used, it has been observed that silicon and salicylic acid are two potential chemicals for inducing resistance against fungal and bacterial diseases in rice, respectively. However, an inclusive evaluation of the potential of different abiotic agents to induce resistance against rice pathogens is lacking due to which the studies on induction of defense against rice pathogens via chemopriming has become disproportionate and discontinuous. The present review deals with a comprehensive analysis of different abiotic agents used to induce defense against rice pathogens, their mode of application, mechanism of defense induction and the effect of defense induction on grain yield. It also provides an account of unexplored areas, which might be taken into attention to efficiently manage rice diseases. DATA AVAILABILITY STATEMENT: Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

Silicate solubilizing and plant growth promoting bacteria interact with biogenic silica to impart heat stress tolerance in rice by modulating physiology and gene expression

Heat stress caused due to increasing warming climate has become a severe threat to global food production including rice. Silicon plays a major role in improving growth and productivity of rice by aiding in alleviating heat stress in rice. Soil silicon is only sparingly available to the crops can be made available by silicate solubilizing and plant-growth-promoting bacteria that possess the capacity to solubilize insoluble silicates can increase the availability of soluble silicates in the soil. In addition, plant growth promoting bacteria are known to enhance the tolerance to abiotic stresses of plants, by affecting the biochemical and physiological characteristics of plants. The present study is intended to understand the role of beneficial bacteria viz. Rhizobium sp. IIRR N1 a silicate solublizer and Gluconacetobacter diazotrophicus, a plant growth promoting bacteria and their interaction with insoluble silicate sources on morpho-physiological and molecular attributes of rice (Oryza sativa L.) seedlings after exposure to heat stress in a controlled hydroponic system. Joint inoculation of silicates and both the bacteria increased silicon content in rice tissue, root and shoot biomass, significantly increased the antioxidant enzyme activities (viz. superoxidase dismutase, catalase and ascorbate peroxidase) compared to other treatments with sole application of either silicon or bacteria. The physiological traits (viz. chlorophyll content, relative water content) were also found to be significantly enhanced in presence of silicates and both the bacteria after exposure to heat stress conditions. Expression profiling of shoot and root tissues of rice seedlings revealed that seedlings grown in the presence of silicates and both the bacteria exhibited higher expression of heat shock proteins (HSPs viz., OsHsp90, OsHsp100 and 60 kDa chaperonin), hormone-related genes (OsIAA6) and silicon transporters (OsLsi1 and OsLsi2) as compared to seedlings treated with either silicates or with the bacteria alone. The results thus reveal the interactive effect of combined application of silicates along with bacteria Rhizobium sp. IIRR N1, G. diazotrophicus inoculation not only led to augmented silicon uptake by rice seedlings but also influenced the plant biomass and elicited higher expression of HSPs, hormone-related and silicon transporter genes leading to improved tolerance of seedling to heat stress.

Silicon Enhances Brassica napus Tolerance to Boron Deficiency by the Remobilisation of Boron and by Changing the Expression of Boron Transporters

Boron (B) is an essential micronutrient for plants, and its deficiency is a widespread nutritional disorder, particularly in high-demanding crops like Brassica napus. Over the past few decades, silicon (Si) has been shown to mitigate plant nutrient deficiencies of different macro- and micro-nutrients. However, the work on B and Si cross-talk has mostly been focused on the alleviation of B toxicity by Si application. In the present study, we investigated the effect of Si application on rapeseed plants grown hydroponically under long-term B deficiency (20 days at 0.1 µM B). In addition, a B-uptake labelling experiment was conducted, and the expression of the genes involved in B uptake were monitored between 2 and 15 days of B shortage. The results showed that Si significantly improved rapeseed plant growth under B deficiency by 34% and 49% in shoots and roots, respectively. It also increased the expression level of BnaNIP5;1 and BOR1;2c in both young leaves and roots. The uptake labelling experiment showed the remobilization of previously fixed ¹¹B from old leaves to new tissues. This study provides additional evidence of the beneficial effects of Si under conditions lacking B by changing the expression of the BnaNIP5;1 gene and by remobilizing ¹¹B to young tissues.

Silicon in Plants: Alleviation of Metal(loid) Toxicity and Consequential Perspectives for Phytoremediation

For the majority of higher plants, silicon (Si) is considered a beneficial element because of the various favorable effects of Si accumulation in plants that have been revealed, including the alleviation of metal(loid) toxicity. The accumulation of non-degradable metal(loid)s in the environment strongly increased in the last decades by intensified industrial and agricultural production with negative consequences for the environment and human health. Phytoremediation, i.e., the use of plants to extract and remove elemental pollutants from contaminated soils, has been commonly used for the restoration of metal(loid)-contaminated sites. In our viewpoint article, we briefly summarize the current knowledge of Si-mediated alleviation of metal(loid) toxicity in plants and the potential role of Si in the phytoremediation of soils contaminated with metal(loid)s. In this context, a special focus is on metal(loid) accumulation in (soil) phytoliths, i.e., relatively stable silica structures formed in plants. The accumulation of metal(loid)s in phytoliths might offer a promising pathway for the long-term sequestration of metal(loid)s in soils. As specific phytoliths might also represent an important carbon sink in soils, phytoliths might be a silver bullet in the mitigation of global change. Thus, the time is now to combine Si/phytolith and phytoremediation research. This will help us to merge the positive effects of Si accumulation in plants with the advantages of phytoremediation, which represents an economically feasible and environmentally friendly way to restore metal(loid)-contaminated sites.

Evapotranspiration-linked silica deposition in a basal tracheophyte plant (Lycopodiaceae: Lycopodiella alopecuroides): implications for the evolutionary origins of phytoliths

Phytoliths, microscopic deposits of hydrated silica within plants, play a myriad of functional roles in extant tracheophytes - yet their evolutionary origins and the original selective pressures leading to their deposition remain poorly understood. To gain new insights into the ancestral condition of tracheophyte phytolith production and function, phytolith content was intensively assayed in a basal, morphologically conserved tracheophyte: the foxtail clubmoss Lycopodiella alopecuroides. Wet ashing was employed to perform phytolith extractions from every major anatomical region of L. alopecuroides. Phytolith occurrence was recorded, alongside abundance, morphometric information, and morphological descriptions. Phytoliths were recovered exclusively from the microphylls, which were apicodistally silicified into multiphytolith aggregates. Phytolith aggregates were larger and more numerous in anatomical regions engaging in greater evapotranspirational activity. The tissue distribution of L. alopecuroides phytoliths is inconsistent with the expectations of proposed adaptive hypotheses of phytolith evolutionary origin. Instead, it is hypothesized that phytoliths may have arisen incidentally in the L. alopecuroides-like ancestral plant, polymerizing from intraplant silicon accumulations arising via bulk flow and 'leaky' cellular micronutrient channels. This basal, nonadaptive phytolith formation model would provide the evolutionary 'raw material' for later modification into the useful, adaptative, phytolith deposits seen in later-diverging plant clades.

Evaluating the Effectiveness of Calcium Silicate in Enhancing Soybean Growth and Yield

The application of silicon (Si) fertilizer positively impacts crop health, yield, and seed quality worldwide. Si is a "quasi-essential" element that is crucial for plant nutrition and stress response but is less associated with growth. This study aimed to investigate the effect of Si on the yield of cultivated soybean (Glycine max L). Two locations, Gyeongsan and Gunwi, in the Republic of Korea were selected, and a land suitability analysis was performed using QGIS version 3.28.1. The experiments at both locations consisted of three treatments: the control, Si fertilizer application at 2.3 kg per plot (9 m × 9 m) (T1), and Si fertilizer application at 4.6 kg per plot (9 m × 9 m) (T2). The agronomic, root, and yield traits, as well as vegetative indices, were analyzed to evaluate the overall impact of Si. The results demonstrated that Si had consistently significant effects on most root and shoot parameters in the two experimental fields, which led to significantly increased crop yield when compared with the control, with T2 (22.8% and 25.6%, representing an output of 2.19 and 2.24 t ha^-1 at Gyeongsan and Gunwi, respectively) showing a higher yield than T1 (11% and 14.2%, representing 1.98 and 2.04 t ha^-1 at Gyeongsan and Gunwi, respectively). These results demonstrate the positive impact of exogenous Si application on the overall growth, morphological and physiological traits, and yield output of soybeans. However, the application of the optimal concentration of Si according to the crop requirement, soil status, and environmental conditions requires further studies.

Nano-biofertilizers as bio-emerging strategies for sustainable agriculture development: Potentiality and their limitations

Nanotechnology is a burgeoning revolutionary technology in the 21st century. Climate emergencies caused by natural or anthropogenic activities have tragically consequential repercussions on agricultural output worldwide. Modern cropping systems profoundly rely on synthetic fertilizers to deliver necessary nutrients, yet their prolonged and persistent administration is hazardous to the environment, soil fertility, and nutritional dynamics of the rhizospheric microbiome. By addressing the drawback of physico-chemically synthesized nano-dimensioned fertilizer, this review emphasizes on integrating nanoparticles and biofertilizers conjointly as nano-biofertilizers (NBF) which can safeguard global food security, in light of the population surge. Inoculation with nanoparticles and biofertilizers strengthens plant growth and stress tolerance. However, combined together (NBF), they have emerged as a more economically and environmentally sustainable, highly versatile, and long-lasting agriculture tool. Microbe-based green synthesis using the encapsulation of inorganic nanoparticles of Si, Zn, Cu, Fe, Ni, Ti, and Ag as well as organic materials, including chitosan, cellulose, and starch, to formulate NBFs can eliminate the constraints of conventional fertilizer contamination. The application of NBFs is in its infancy in agriculture, yet it has promising potential for transforming traditional farming techniques into smart agriculture, compared to any of the existing strategies. From this perspective, this review is an attempt to provide a comprehensive understanding of the formulations, fabrication, and characterization of NBFs while unraveling the underlying mechanisms of plant-NBF interactions along with their contribution to climate change-induced biotic and abiotic stress tolerance. We substantially summarize the latest advancements of field applications of NBFs for precision farming. Moreover, we critically revised their applications in agro-ecosystems according to the current literature, while also discussing the bottlenecks and future trends for developing potent NBFs.

The changes in the physicochemical properties of calcareous soils and the factors of arsenic (As) uptake by wheat were investigated after the cessation of effluent irrigation for nearly 20 years

It is not known what the buffering capacity of soils and arsenic (As) enrichment by crops is for calcareous agricultural soils after the end of long-term effluent irrigation. In this study, changes in soil physicochemical properties and factors of influencing As uptake by wheat were investigated in agricultural soils where sewage irrigation had been ceased for nearly 20 years. The results showed that the content of CaCO₃ and pH in soil increased compared to the period before the cessation of sewage irrigation, but remained below the soil background value. Furthermore, CaCO₃ is by far the main buffering substance in agricultural soils and indirectly contributes to the increase in pH. The As concentration in the soil was 36.4 ± 34.8 mg/kg, which was 0.56-10.28 times and 0.28-5.18 times higher than the soil background and risk screening values, respectively, but showed a decreasing trend. pH and Fe dissolution were the main reasons for the lower As concentration in the soil. Total As in soil was a better predictor of As in wheat, and soil electrical conductivity (EC) and soil organic matter (SOM) promoted As uptake by wheat. The competitive uptake of As by dissolved Si was an important reason for the mismatch between As concentrations in soil and wheat. This study highlighted the key issues of As transport transformation in soil-wheat systems after cessation of effluent irrigation, using agricultural soils, and provided a reference for soil risk management in agricultural soils in mining areas.

Impact of Silicon on Plant Nutrition and Significance of Silicon Mobilizing Bacteria in Agronomic Practices

Globally, rejuvenation of soil health is a major concern due to the continuous loss of soil fertility and productivity. Soil degradation decreases crop yields and threatens global food security. Improper use of chemical fertilizers coupled with intensive cultivation further reduces both soil health and crop yields. Plants require several nutrients in varying ratios that are essential for the plant to complete a healthy growth and development cycle. Soil, water, and air are the sources of these essential macro- and micro-nutrients needed to complete plant vegetative and reproductive cycles. Among the essential macro-nutrients, nitrogen (N) plays a significant in non-legume species and without sufficient plant access to N lower yields result. While silicon (Si) is the 2nd most abundant element in the Earth’s crust and is the backbone of soil silicate minerals, it is an essential micro-nutrient for some plants. Silicon is just beginning to be recognized as an important micronutrient to some plant species and, while it is quite abundant, Si is often not readily available for plant uptake. The manufacturing cost of synthetic silica-based fertilizers is high, while absorption of silica is quite slow in soil for many plants. Rhizosphere biological weathering processes includes microbial solubilization processes that increase the dissolution of minerals and increases Si availability for plant uptake. Therefore, an important strategy to improve plant silicon uptake could be field application of Si-solubilizing bacteria. In this review, we evaluate the role of Si in seed germination, growth, and morphological development and crop yield under various biotic and abiotic stresses, different pools and fluxes of silicon (Si) in soil, and the bacterial genera of the silicon solubilizing microorganisms. We also elaborate on the detailed mechanisms of Si-solubilizing/mobilizing bacteria involved in silicate dissolution and uptake by a plant in soil. Last, we discuss the potential of silicon and silicon solubilizing/mobilizing to achieve environmentally friendly and sustainable crop production.

Exogenous nano-silicon application improves ion homeostasis, osmolyte accumulation and palliates oxidative stress in Lens culinaris under NaCl stress

Lentil is one of the highly nutritious legumes but is highly susceptible to salinity stress. Silicon has been known to reduce the effect of various environmental stresses including salinity. Moreover, silicon when applied in its nano-form is expected to augment the beneficial attributes of silicon. However, very little is known regarding the prospect of nano-silicon (nSi) application for alleviating the effect of salinity stress in non-silicified plants like lentil. In this study, the primary objective was to evaluate the efficacy of nSi in the alleviation of NaCl stress during germination and early vegetative stages. In this context, different concentrations of nSi (0, 1, 5, 10 g L-1) was applied along with four different concentrations of NaCl (0, 100, 200, 300 mM). The results indicated the uptake of nSi which was confirmed by the better accumulation of silica in the plant tissues. Most importantly, the enhanced accumulation of silica increased the K+/Na+ ratio of the NaCl-stressed seedlings. Moreover, nSi efficiently improved germination, growth, photosynthetic pigments, and osmotic balance. On the other hand, the relatively reduced activities of antioxidative enzymes were surmounted by the higher activity of non-enzymatic antioxidants which mainly scavenged the increased ROS. Reduced ROS accumulation in return ensured better membrane integrity and reduced electrolyte leakage up on nSi application. Therefore, it can be concluded that the application of nSi (more specifically at 10 g L-1) facilitated the uptake of silica and improved the K+/Na+ ratio to reclaim the growth and physiological status of NaCl-stressed seedlings.

Large-Scale Synthesis of Nanosilica from Silica Sand for Plant Stimulant Applications

Nanosilica is a versatile nanomaterial suitable as, e.g., drug carriers in medicine, fillers in polymers, and fertilizer/pesticide carriers and potentially a bioavailable source of silicon in agriculture. The enhanced biological activity of nanosilica over quartz sand has been noted before; it is directly related to the altered physicochemical properties of the nanoparticles compared to those of the bulk material. Therefore, it is feasible to use nanosilica as a form of plant stimulant. Nanosilica synthesis is a relatively cheap routine process on the laboratory scale; however, it is not easily scalable. Largely for this reason, studies of nanosilica fertilizers are scarce. This study will focus on industrial-scale silica nanoparticle production and the application of nanosilica as a plant stimulant in maize. A variant of the sol-gel method is used to successfully synthesize nanosilica particles starting from silica sand. The resulting particles are in the size range of 16-37 nm with great purity. The potential of nanosilica as a plant stimulant is demonstrated with the increased quantity and quality of maize crops.

Effects of silica soil amendment against Exserohilum rostratum, the fungal pathogen of rice brown spot disease in Peninsular Malaysia

Rice brown spot (BS) exerts devastating agronomic effects on grain quality and overall productivity. In Peninsular Malaysia, BS disease incidence is fairly prevalent and little is known about the diversity of BS pathogens in the local granaries. Fifteen isolates from BS symptomatic rice plants were identified at five different rice granaries across Peninsular Malaysia. Based on the morphological and molecular analyses, two isolates were confirmed as Bipolaris oryzae while the rest were identified as Exserohilum rostratum. Phylogenetic tree analysis revealed that BS incidence in rice granaries in Peninsular Malaysia is caused by a pair of closely related fungal pathogens, E. rostratum and B. oryzae, with the former being more predominant. Cultural characterization of E. rostratum isolate KT831962 showed the best growth and sporulation activity on corn meal agar plates incubated in complete darkness. The effects of calcium silicate (CaSiO₃) and rice husk ash (RHA) soil amendment against MR219 and MR253 rice varieties were evaluated during rice-E. rostratum interaction. Results showed that soil amelioration using CaSiO₃ and RHA singly and in combination with manganese (Mn) significantly reduced rice BS disease severity. The BS disease index was reduced significantly to less than 31.6% in the silicon-treated rice plants relative to the control plants at 41.2%. Likewise, the grain yield at the harvest stage showed significantly higher yield in the Si-treated rice plants in comparison to the control, non-Si treated rice plants. The findings highlight the potential of RHA agro-waste as Si fertilizer in a sustainable rice production system.

Silicon as a Smart Fertilizer for Sustainability and Crop Improvement

Silicon (Si), despite being abundant in nature, is still not considered a necessary element for plants. Si supplementation in plants has been extensively studied over the last two decades, and the role of Si in alleviating biotic and abiotic stress has been well documented. Owing to the noncorrosive nature and sustainability of elemental Si, Si fertilization in agricultural practices has gained more attention. In this review, we provide an overview of different smart fertilizer types, application of Si fertilizers in agriculture, availability of Si fertilizers, and experiments conducted in greenhouses, growth chambers, and open fields. We also discuss the prospects of promoting Si as a smart fertilizer among farmers and the research community for sustainable agriculture and yield improvement. Literature review and empirical studies have suggested that the application of Si-based fertilizers is expected to increase in the future. With the potential of nanotechnology, new nanoSi (NSi) fertilizer applications may further increase the use and efficiency of Si fertilizers. However, the general awareness and scientific investigation of NSi need to be thoughtfully considered. Thus, we believe this review can provide insight for further research into Si fertilizers as well as promote Si as a smart fertilizer for sustainability and crop improvement.

Mineral-Soil-Plant-Nutrient Synergisms of Enhanced Weathering for Agriculture: Short-Term Investigations Using Fast-Weathering Wollastonite Skarn

Enhanced weathering is a proposed carbon dioxide removal (CDR) strategy to accelerate natural carbon sequestration in soils via the amendment of silicate rocks to agricultural soils. Among the suitable silicates (such as basalt and olivine), the fast-weathering mineral wollastonite (CaSiO₃) stands out. Not only does the use of wollastonite lead to rapid pedogenic carbonate formation in soils, it can be readily detected for verification of carbon sequestration, but its weathering within weeks to months influences soil chemistry and plant growth within the same crop cycle of its application. This enables a variety of short-term experimental agronomic studies to be conducted to demonstrate in an accelerated manner what could take years to be observed with more abundant but slower weathering silicates. This study presents the results of three studies that were conducted to investigate three distinct aspects of wollastonite skarn weathering in soils in the context of both agricultural and horticultural plants. The first study investigated the effect of a wide range of wollastonite skarn dosages in soil (1.5-10 wt.%) on the growth of green beans. The second study provides insights on the role of silicon (Si) release during silicate weathering on plant growth (soybeans and lettuce). The third study investigated the effect of wollastonite skarn on the growth of spring rye when added to soil alongside a nitrogen-based coated fertilizer. The results of these three studies provide further evidence that amending soil with crushed silicate rocks leads to climate-smart farming, resulting in inorganic carbon sequestration, as well as better plant growth in agricultural (soybean and spring rye) and horticultural (green bean and lettuce) crops. They also demonstrate the value of working with wollastonite skarn as a fast-weathering silicate rock to accelerate our understanding of the mineral-soil-plant-nutrient synergism of enhanced weathering.

Reuse of poor-quality water for sustainable crop production in the changing scenario of climate

The availability of freshwater is limited for agriculture systems across the globe. A fast-growing population demands need to enhance the food grain production from a limited natural resources. Therefore, researchers and policymakers have been emphasized on the production potential of agricultural crops in a sustainable manner. On the challenging side, freshwater bodies are shrinking with the pace of time further limiting crop production. Poor-quality water may be a good alternative for fresh water in water scarce areas. It should not contain toxic pollutants beyond certain critical levels. Unfortunately, such critical limits for different pollutants as well as permissible quality parameters for different wastewater types are lacking or poorly addressed. Marginal quality water and industrial effluent used in crop production should be treated prior to application in crop field. Hence, safe reuse of wastewater for cultivation of food material is necessary to fulfil the demands of growing population across the globe in the changing scenario of climate.

The Multiple Role of Silicon Nutrition in Alleviating Environmental Stresses in Sustainable Crop Production

In addition to the application of macronutrients (N, P, K), there has been an increasing interest in studying the effects of different micronutrients on growth and development in plant populations under abiotic and biotic stresses. Experimental results have demonstrated the role of silicon in mitigating environmental stresses on plants (especially in silicon accumulating plant species). Furthermore, as the silicon content of soils available to plants can vary greatly depending on soil type, the many positive results have led to increased interest in silicon as a nutrient in sustainable agriculture over the last decade. The grouping of plant species according to silicon accumulation is constantly changing as a result of new findings. There are also many new research results on the formation of phytoliths and their role in the plants. The use of silicon as a nutrient is becoming more widespread in crop production practices based on research results reporting beneficial effects. Controversial results have also been obtained on the use of different Si-containing materials as fertilizers. Many questions remain to be clarified about the uptake, transport, and role of silicon in plant life processes, such as stress management. Future research is needed to address these issues. This review discusses the role and beneficial effects of silicon in plants as a valuable tool for regulating biological and abiotic stresses. Our aim was to provide an overview of recent research on the role and importance of silicon in sustainable crop production and to highlight possible directions for further research.

Effect of silicon application with mycorrhizal inoculation on Brassica juncea cultivated under water stress

Brassica juncea L. is a significant member of the Brassicaceae family, also known as Indian mustard. Water is a limiting factor in the successful production of this crop. Here, we tested the effect of water shortage in B. juncea plants supplemented with or without the application of silicon and arbuscular mycorrhizal fungi in total 8 different treatments compared under open filed conditions using a randomised complete block design (RCBD). The treatments under control conditions were control (C, T1); C+Silicon (Si, T2); C+My (Mycorrhiza; T3); and C+Si+My (T4). In contrast, treatments under stress conditions were S (Stress; T5); S+Si (T6); S+My (T7) and S+Si+My (T8), respectively. In total, we evaluated 16 traits, including plant response to stress by evaluating peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity. The fresh weight (g) increased only 7.47 percent with mycorrhiza (C+My) and 22.39 percent with silicon (C+Si) but increased 291.08 percent with both mycorrhiza and silicon (C+Si+My). Using mycorrhiza (S+My) or silicon (S+Si) alone produced a significant increase of 53.16 percent and 55.84 percent in fresh weight, respectively, while using both mycorrhiza and silicon (S+Si+My) together produced a dramatic increase of 380.71 percent under stress conditions. Superoxidase dismutase concentration (Ug⁻¹ FW) was found to be increased by 29.48 percent, 6.71 percent, and 22.63 percent after applying C+My, C+Si and C+Si+My, but treatment under stress revealed some contrasting trends, with an increase of 11.21 percent and 19.77 percent for S+My, S+Si+My, but a decrease of 13.15 percent for S+Si. Finally, in the presence of stress, carotenoid content (mg/g FW) increased by 58.06 percent, 54.83 percent, 183.87 percent with C+My, and 23.81 percent with S+My and S+Si+My, but decreased by 22.22 percent with S+Si. Silicon application proved to be more effective than AMF treatment with Rhizophagus irregularis, and the best results were obtained with the combination of Si and AMF. This work will help to suggest the measures to overcome the water stress in B. juncea.

Diversification Options in Sugarcane-Based Cropping Systems for Doubling Farmers' Income in Subtropical India

Crop diversification provides an opportunity for farmers to maximize their profits, fulfilling multiple needs, avoid monsoon threats, and make the crop production system sustainable. Inclusion of various pulse/oilseed/vegetables/cereals/medicinal/aromatic crops with sugarcane brings forth cultivation of these crops in irrigated agro-system and improves the yields of component crops. Besides, the component crops improve soil fertility and create a favorable environment for the further growth of sugarcane crops. Sprouting in winter-initiated sugarcane ratoon could be enhanced by adopting fodder legumes such as Indian clover and Egyptian clover. Intercropping vegetables provides an ample opportunity for mid-season income generation and improves profitability. Besides, high-value medicinal and aromatic crops such as tulsi (holy basil), mentha could also be included in the sugarcane-based system. Crop residue management has been recognized as a critical issue in managing the crops in the various cropping systems. Including multiple bio-agents for fast decomposition of crop residues provides scope for managing soil organic carbon through crop residue recycling in the system. Resource use efficiencies, nutrient use, water use, and weed control could be increased by adopting suitable crops in intercropping systems. An integrated farming system involving crop, livestock, and fisheries options could improve farmers' profit besides employment generation in rural India. Recycling of bye products and co-products of other enterprises influences the viability and farmer's profitability of the system. Trash, press mud cake, vinasse, composted bagasse, rhizodeposition of stubble play a significant role in sustaining soil fertility and increasing crop productivity. New emerging crop diversification options, viz., intercropping of rajmash, winter maize, and garlic in autumn cane generate mid-season income and enhance the system's profitability for small and marginal cane growers. Dual-purpose legumes, viz., cowpea, and green gram as intercrops with spring-planted cane increase the pool of soil microbial biomass nitrogen capitalize allelopathic effects and sustain soil health. In the present paper, these issues have been discussed. Due to the adoption of location-specific and farmers-centric systems, farmers' profitability could be increased, providing sustainability to the sugarcane-based systems.

Improvement of Selected Morphological, Physiological, and Biochemical Parameters of Roselle (Hibiscus sabdariffa L.) Grown under Different Salinity Levels Using Potassium Silicate and Aloe saponaria Extract

Two successive field trials were carried out at the experimental farm of the Agriculture Department of Fayoum University, Fayoum, Egypt, to investigate the sole or dual interaction effect of applying a foliar spray of Aloe saponaria extract (Ae) or potassium silicate (KSi) on reducing the stressful salinity impacts on the development, yield, and features of roselle (Hibiscus sabdariffa L.) plants. Both Ae or KSi were used at three rates: 0% (0 cm3 L-1), 0.5% (5 cm3 L-1), and 1% (10 cm3 L-1) and 0, 30, and 60 g L-1, respectively. Three rates of salinity, measured by the electrical conductivity of a saturated soil extract (ECe), were also used: normal soil (ECe < 4 dS/m) (S1); moderately-saline soil (ECe: 4-8 dS/m) (S2); and highly-saline soil (ECe: 8-16 dS/m) (S3). The lowest level of salinity yielded the highest levels of all traits except for pH, chloride, and sodium. Ae at 0.5% increased the values of total soluble sugars, total free amino acids, potassium, anthocyanin, a single-photon avalanche diode, stem diameter, fruit number, and fresh weight, whereas 1% of Ae resulted in the highest plant height, chlorophyll fluorescence (Fv/Fm), performance index, relative water content, membrane stability index, proline, total soluble sugars, and acidity. KSi either at 30 or 60 g L-1 greatly increased these abovementioned attributes. Fruit number and fruit fresh weight per plant also increased significantly with the combination of Ae at 1% and KSi at 30 g L-1 under normal soil conditions.

Impact of Silica Ions and Nano Silica on Growth and Productivity of Pea Plants under Salinity Stress

The present study was conducted to evaluate the effects of silicon (Si) and nano-silicon (NSi) on growth, yield, ions content, and antioxidant defense systems, including transcript levels of enzyme-encoding genes in Pisum sativum plants grown under salinity stress. Both Si and NSi were applied at the 3 mM level and NaCl was applied at 4 concentrations (100, 150, 200 and 250 mM). Vegetative growth, including plant height, leaf area, fresh and dry weights, and yield attributes were determined. Gene expression of antioxidant enzymes was analyzed, and their activities were determined. The results showed that salinity had deleterious effects on plant growth and yield. Salt-stressed plant leaves exhibited a greater activity of superoxide dismutase (SOD), peroxidase (POD), but a lower activity of catalase (CAT) when compared to the control. Na⁺ ions accumulated in roots and shoots of salinized plants. The application of Si and NSi significantly enhanced vegetative growth and relative water content (RWC), and caused significant increases in plant height, fresh and dry weight, total yield, and antioxidant defense systems. Si and NSi enhanced K⁺ content in roots and shoots under salinity treatment and decreased Na⁺ content in the studied tissues. It was concluded that the application of NSi was beneficial in improving the salt tolerance of Pisum sativum plants more than Si alone.

Remineralizing soils? The agricultural usage of silicate rock powders: A review

Soil nutrient depletion threatens global food security and has been seriously underestimated for potassium (K) and several micronutrients. This is particularly the case for highly weathered soils in tropical countries, where classical soluble fertilizers are often not affordable or not accessible. One way to replenish macro- and micronutrients are ground silicate rock powders (SRPs). Rock forming silicate minerals contain most nutrients essential for higher plants, yet slow and inconsistent weathering rates have restricted their use in the past. Recent findings, however, challenge past agronomic objections which insufficiently addressed the factorial complexity of the weathering process. This review therefore first presents a framework with the most relevant factors for the weathering of SRPs through which several outcomes of prior studies can be explained. A subsequent analysis of 48 crop trials reveals the potential as alternative K source and multi-nutrient soil amendment for tropical soils, whereas the benefits for temperate soils are currently inconclusive. Beneficial results prevail for mafic and ultramafic rocks like basalts and rocks containing nepheline or glauconite. Several rock modifications are highly efficient in increasing the agronomic effectiveness of SRPs. Enhanced weathering of SRPs could additionally sequester substantial amounts of CO₂ from the atmosphere and silicon (Si) supply can induce a broad spectrum of plant biotic and abiotic stress resistance. Recycling massive amounts of rock residues from domestic mining industries could furthermore resolve serious disposal challenges and improve fertilizer self-sufficiency. In conclusion, under the right circumstances, SRPs could not only advance low-cost and regional soil sustaining crop production but contribute to various sustainable development goals.

Mitigating the Negative Effect of Drought Stress in Oat (Avena sativa L.) with Silicon and Sulphur Foliar Fertilization

A field experiment was carried out in the 2020-2021 growing season, aiming at investigating the abiotic stress tolerance of oat (Avena sativa L.) with silicon and sulphur foliar fertilization treatments and monitoring the effect of treatments on the physiology, production and stress tolerance of winter oat varieties. In the Hungarian national list of varieties, six winter oat varieties were registered in 2020, and all of the registered varieties were sown in a small plot field experiment in Debrecen, Hungary. The drought tolerance of the oat could be tested, because June was very dry in 2021; the rainfall that month totaled 6 mm only despite a 30-year average of 66.5 mm, and the average temperature for the month was 3.2 °C higher than the 30-year average. Foliar application of silicon and sulphur fertilizers caused differences in the photosynthesis rate, total conductance to CO₂, transpiration, water use efficiency, leaf area, chlorophyll content, carotenoid content, thousand kernel weight (TKW) and yield of winter oat. The application of silicon significantly increased the photosynthesis rate (16.8-149.3%), transpiration (5.4-5.6%), air-leaf temperature difference (16.2-43.2%), chlorophyll (1.0%) and carotenoid (2.5%) content. The yield increased by 10.2% (Si) and 8.0% (Si plus S), and the TKW by 3.3% (Si) and 5.0% (Si plus S), compared to the control plots. The plants in the control plots assimilated less CO₂ while transpiring 1 m³ water more than in the Si, S or Si plus S fertilized plots. The effect of the silicon varied from 9.0 to 195.4% in water use efficiency (WUE) in the three development stages (BBCH52, BBCH65 and BBCH77). A lower leaf area index was measured in the foliar fertilized plots; even so, the yield was higher, compared to that from the control plots. Great variation was found in response to the foliar Si and S fertilization among winter oat varieties-in WUE, 2.0-43.1%; in total conductance to CO₂, 4.9-37.3%; in leaf area, 1.6-34.1%. Despite the droughty weather of June, the winter oat varieties produced a high yield. The highest yield was in 'GK Arany' (7015.7 kg ha^-1), which was 23.8% more than the lowest yield ('Mv Kincsem', 5665.6 kg ha ^-1). In the average of the treatments, the TKW increased from 23.9 to 33.9 g (41.8%). 'Mv Hópehely' had the highest TKW. Our results provide information about the abiotic stress tolerance of winter oat, which, besides being a good model plant because of its drought resistance, is an important human food and animal feed.

Multifaceted roles of silicon in mitigating environmental stresses in plants

Food security relies on plant productivity and plant's resilience to climate change driven environmental stresses. Plants employ diverse adaptive mechanisms of stress-signalling pathways, antioxidant defense, osmotic adjustment, nutrient homeostasis and phytohormones. Over the last few decades, silicon has emerged as a beneficial element for enhancing plant growth productivity. Silicon ameliorates biotic and abiotic stress conditions by regulating the physiological, biochemical and molecular responses. Si-uptake and transport are facilitated by specialized Si-transporters (Lsi1, Lsi2, Lsi3, and Lsi6) and, the differential root anatomy has been shown to reflect in the varying Si-uptake in monocot and dicot plants. Silicon mediates a number of plant processes including osmotic, ionic stress responses, metabolic processes, stomatal physiology, phytohormones, nutrients and source-sink relationship. Further studies on the transcriptional and post-transcriptional regulation of the Si transporter genes are required for better uptake and transport in spatial mode and under different stress conditions. In this article, we present an account of the availability, uptake, Si transporters and, the role of Silicon to alleviate environmental stress and improve plant productivity.

The mechanisms of silicon on maintaining water balance under water deficit stress

Water deficit stress severely threatens crop yield and numerous reports have shown silicon could enhance plants resistance to water deficit. One of the most important mechanisms is that silicon maintains the water balance. In this review, we summarized advanced research to elucidate the effect of silicon on plant water transport processes, including leaf water loss, vessel water transport, and root water uptake. In leaves, the deposition of silica phytolith on cuticle and stomata decreases transpirational water loss under water deficit stress. However, accumulating evidence suggest that silicon maintaining leaf water content is not through reducing water loss, but through osmotic adjustments, enhancing water transport and uptake. Enhancement of stem water transport efficiency by silicon is due to silica phytolith depositing in the cell wall of vessel tubes and pits, which support it avoiding to collapse and embolism, respectively. The improvement of root water uptake capacity by silicon acts as a key role in maintaining water balance. The underlying mechanisms include (i) enlargement of the root water uptake area, (ii) improvement of the water driving force, (iii) the prevention of water loss from root to soil, and (iv) the up-regulation of aquaporin activity. This review provides three simple models to understand the mechanism of silicon on water balance and highlights the future research area.

Arbuscular mycorrhizae and silicon alleviate arsenic toxicity by enhancing soil nutrient availability, starch degradation and productivity in Cajanus cajan (L.) Millsp

Arsenic (As) pollution of soil reduces the growth and reproductive potential of plants. Silicon (Si) and arbuscular mycorrhizal (AM) fungi play significant roles in alleviating adverse effects of As stress. However, studies are scant regarding alleviative effects of Si in pigeonpea (Cajanus cajan L. Millsp.) because legumes are considered low Si-accumulators. We investigated the individual as well as synergistic potential of Si with two AM species (M1-Claroideoglomus etunicatum and M2-Rhizoglomus intraradices) in modulating soil properties, thereby improving growth and productivity of pigeonpea genotype Pusa 2001 grown in AsV and AsIII challenged soils. Both As species hampered the establishment of AM symbiosis, thus, reducing nutrient uptake, growth and yield, with AsIII more toxic than AsV. Exogenously applied Si and AM species enhanced soil glomalin and phosphatases activity, hence decreased metal bioavailability in soil, increased plant nutrient acquisition, biomass and chlorophylls; with maximum benefits provided by M2, closely followed by Si and least by M1. These amendments boosted the activities of starch hydrolytic enzymes (α-, β-amylase, starch phosphorylase) in plants, along with a simultaneous increase in total soluble sugars (TSS). This enhanced sugar accumulation directly led to improved reproductive attributes, more efficiently by M2 and Si than by M1. Moreover, there was a substantial increase in proline biosynthesis due to significantly enhanced activities of its biosynthetic enzymes. Additionally, combined applications of Si and AM, especially +Si+M2, complemented each other where AM enhanced Si uptake, while Si induced mycorrhization, suggesting their mutual and beneficial roles in ameliorating metal(loid) toxicity and achieving sustainability in pigeonpea production under As stress.

Influence of Silicon on Biocontrol Strategies to Manage Biotic Stress for Crop Protection, Performance, and Improvement

Silicon (Si) has never been acknowledged as a vital nutrient though it confers a crucial role in a variety of plants. Si may usually be expressed more clearly in Si-accumulating plants subjected to biotic stress. It safeguards several plant species from disease. It is considered as a common element in the lithosphere of up to 30% of soils, with most minerals and rocks containing silicon, and is classified as a "significant non-essential" element for plants. Plant roots absorb Si, which is subsequently transferred to the aboveground parts through transpiration stream. The soluble Si in cytosol activates metabolic processes that create jasmonic acid and herbivore-induced organic compounds in plants to extend their defense against biotic stressors. The soluble Si in the plant tissues also attracts natural predators and parasitoids during pest infestation to boost biological control, and it acts as a natural insect repellent. However, so far scientists, policymakers, and farmers have paid little attention to its usage as a pesticide. The recent developments in the era of genomics and metabolomics have opened a new window of knowledge in designing molecular strategies integrated with the role of Si in stress mitigation in plants. Accordingly, the present review summarizes the current status of Si-mediated plant defense against insect, fungal, and bacterial attacks. It was noted that the Si-application quenches biotic stress on a long-term basis, which could be beneficial for ecologically integrated strategy instead of using pesticides in the near future for crop improvement and to enhance productivity.

Role of silicon in elevating resistance against sheath blight and blast diseases in rice (Oryza sativa L.)

Rice blast caused by Magnaporthe oryzae and sheath blight caused by Rhizoctonia solani, are the two major diseases of rice that cause enormous losses in rice production worldwide. Identification and utilization of broad-spectrum resistance resources have been considered sustainable and effective strategies. However, the majority of the resistance genes and QTLs identified have often been found to be race-specific, and their resistance is frequently broken down due to continuous exposure to the pathogen. Therefore, integrated approaches to improve plant resistance against such devastating pathogen have great importance. Silicon (Si), a beneficial element for plant growth, has shown to provide a prophylactic effect against many pathogens. The application of Si helps the plants to combat the disease-causing pathogens, either through its deposition in different parts of the plant or through modulation/induction of specific defense genes by yet an unknown mechanism. Some reports have shown that Si imparts resistance to rice blast and sheath blight. The present review summarizes the mechanism of Si transport and deposition and its effect on rice growth and development. A special emphasis has been given to explore the existing evidence showing Si mediated blast and sheath blight resistance and the mechanism involved in resistance. This review will help to understand the prophylactic effects of Si against sheath blight and blast disease at the mechanical, physiological, and genetic levels. The information provided here will help develop a strategy to explore Si derived benefits for sustainable rice production.

Silicon enhancement for endorsement of Xanthomonas albilineans infection in sugarcane

Silicon (Si) is considered to be a plant growth and development regulator element as well as provide the regulatory response against various biotic stressors. However, the potential mechanism of Si enhancement to regulate plant disease resistance remains to be studied. Therefore, the current study evaluated the effects of Si application on the performance of sugarcane against Xanthomonas albilineans (Xa) infection. Si was applied exogenously (0, 3.85 and 7.70 g Si/kg soil) and the results show that plant height, stem circumference and leaf width of siliconized sugarcane have been improved, which effectively reduced the disease index (0.17-0.21) and incidence (58.2%-69.1%) after Xa infection. Lowest values of MDA (348.5 nmol g^-1 FW) and H₂O₂ (3539.4 mmol/L) were observed in 7.70 g Si/kg soil followed by in 3.85 g Si/kg soil (MDA: 392.6 nmol g^-1 FW and H₂O₂: 3134.6 mmol/L) than that of the control. Whereas, PAL enzyme activity (50.8 mmol/L), JA (230.2 mmol/L) and SA (2.7 ug mL^-1) contents were significantly higher in 7.70 g Si/kg soil followed by in 3.85 g Si/kg soil (PAL: 46.3 mmol/L, JA: 182.7 mmol/L and SA: 2.4 ug mL^-1) as compared to control. The lower MDA, H₂O₂ level and higher enzymatic activities were associated with the highest expression levels of their metabolic pathway associated genes i.e., ShMAPK1, ShLOX, ShPAL, ShAOS, ShAOC, ShC4H, ShCAT, Sh4CL and ShNPR1 (22.08, 15.56, 10.42, 3.35, 2.54, 2.14, 1.82, 1.67 and 1.22 folds, respectively) in 7.70 g Si/kg soil as compared to other experimental units and control. Overall, the results of current study indicates that siliconized sugarcane more actively regulates disease resistance through modulation of growth and MDA, H₂O₂, SA and JA associated metabolic pathways.

Exploration of silicate solubilizing bacteria for sustainable agriculture and silicon biogeochemical cycle

Silicon (Si), a quasi-essential element for plants, is abundant in the soil typically as insoluble silicate forms. However, plants can uptake Si only in the soluble form of monosilicic acid. Production of monosilicic acid by rock-weathering mostly depends on temperature, pH, redox-potential, water-content, and microbial activities. In the present review, approaches involved in the efficient exploration of silicate solubilizing bacteria (SSB), its potential applications, and available technological advances are discussed. Present understanding of Si uptake, deposition, and subsequent benefits to plants has also been discussed. In agricultural soils, pH is found to be one of the most critical factors deciding silicate solubilization and the formation of different Si compounds. Numerous studies have predicted the role of Indole-3-Acetic Acid (IAA) and organic acids produced by SSB in silicate solubilization. In this regard, approaches for the isolation and characterization of SSB, quantification of IAA, and subsequent Si solubilization mechanisms are addressed. Phylogenetic evaluation of previously reported SSB showed a highly diverse origin which provides an opportunity to study different mechanisms involved in Si solubilization. Soil biochemistry in concern of silicon availability, microbial activity and silicon mediated changes in plant physiology are addressed. In addition, SSB's role in Si-biogeochemical cycling is summarized. The information presented here will be helpful to explore the potential of SSB more efficiently to promote sustainable agriculture.

Influence of Nano Silicon and Nano Selenium on Root Characters, Growth, Ion Selectivity, Yield, and Yield Components of Rice (Oryza sativa L.) under Salinity Conditions

Rice production under salinity stress is a critical challenge facing many countries, particularly those in arid and semi-arid regions. This challenge could be handled by applying novel approaches to overcome yield limiting factors and improve resource use efficiency. The usage of nanoparticles (NPs) could be a beneficial approach to managing the growing problem of soil salinity. The aim of our study was to investigate the advantageous effects of soaking and foliar application of silicon (Si) and selenium (Se), (NPs-Si at 12.5 mg L^-1 and NPs-Se at 6.25 mg L^-1) on root characteristics, moropho-physiological traits, and yields of two rice varieties (i.e., Giza 177 as a salt sensitive and Giza 178 as a salt tolerant) grown in saline soil compared to untreated plants (control treatment). Results showed that soaking NPs-Se resulted in the highest value of root thickness for Giza 178 (0.90 mm, 0.95 mm) and root volume (153.30 cm³, 154.30 cm³), while Giza 177 recorded 0.83 mm, 0.81 mm for root thickness and 143.30 cm³, 141.30 cm³ for root volume in the 2018 and 2019 seasons, respectively. Soaking NPs-Se, NPs-Si and foliar application of NPs-Se at BT resulted in the highest relative water content and dry matter, while foliar application of NPs-Si at BT gave the highest leaf area index of rice plants compared to the other treatments. Giza 178 (i.e., salt tolerant variety) significantly surpassed Giza 177 (i.e., salt sensitive variety) in the main yield components such as panicle number and filled grains/ panicle, while Giza 177 significantly exceeded Giza 178 in the panicle weight, 1000-grain weight, and unfilled grains number/ panicle. Soaking NPs-Se and foliar application of NPs-Si at BT resulted in the highest grain yield of 5.41 and 5.34 t ha^-1 during 2018 and 5.00 and 4.91 t ha^-1 during 2019, respectively. The salt sensitive variety (Giza 177) had the highest Na⁺ leaf content and Na⁺/K⁺ ratio as well as the lowest K+ leaf content during both seasons. Applying nano nutrients such as NPs-Si and NPs-Se improved the yield components of the salt sensitive variety (Giza 177) by enhancing its ion selectivity. Both NPs-Si and NPs-Se had almost the same mode of action to mitigate the harmful salinity and enhance plant growth, and subsequently improved the grain yield. In summary, the application of NPs-Si and NPs-Se is recommended as a result of their positive influence on rice growth and yield as well as minimizing the negative effects of salt stress.

Evaluation on soil fertility quality under biochar combined with nitrogen reduction

A two-year consecutive field experiment was conducted in purple soil in southwest China, to clarify the effects of biochar (0, 10, 20 and 40 t ha⁻¹, namely, B0, B10, B20 and B40) combined with nitrogen reduction (100%, 80% and 60% of conventional nitrogen application rate, namely, N100, N80 and N60) on soil fertility. The performance of thirty-four indices related to soil chemical, physical and biological properties was evaluated by gray correlation analysis, principal component analysis and cluster analysis to determine the most appropriate mode for soil fertilization, and to identify the main soil environmental factors affecting rapeseed yield under the biochar combined with nitrogen reduction. The results indicated that available phosphorus, geometric mean diameter of water stability, fungi number, and the utilization of sugars, amino acids, polymers and carboxylic acids by microorganisms could be used as the main soil factors affecting rapeseed yield. The highest score of soil quality was observed in N100B10 treatment, followed by N80B10 and N100B20 treatments, which were almost in line with the results of rapeseed yields. Cluster analysis classified 12 treatments into 5 main groups on the basis of the measured parameters, which was mostly consistent with the result of soil quality scores. Considering both economic and environmental benefits, 10 t ha⁻¹ biochar combined with 144 kg ha⁻¹ nitrogen was the best combination to restore crop productivity and soil quality, and to achieve nitrogen decreasing and benefit increasing. This study provided scientific basis for the rational fertilization and scientific management of biochar combined with nitrogen fertilizer in purple soil area of southwest China.

Contribution of Arbuscular Mycorrhizal Fungi, Phosphate-Solubilizing Bacteria, and Silicon to P Uptake by Plant

Phosphorus (P) availability is usually low in soils around the globe. Most soils have a deficiency of available P; if they are not fertilized, they will not be able to satisfy the P requirement of plants. P fertilization is generally recommended to manage soil P deficiency; however, the low efficacy of P fertilizers in acidic and in calcareous soils restricts P availability. Moreover, the overuse of P fertilizers is a cause of significant environmental concerns. However, the use of arbuscular mycorrhizal fungi (AMF), phosphate-solubilizing bacteria (PSB), and the addition of silicon (Si) are effective and economical ways to improve the availability and efficacy of P. In this review the contributions of Si, PSB, and AMF in improving the P availability is discussed. Based on what is known about them, the combined strategy of using Si along with AMF and PSB may be highly useful in improving the P availability and as a result, its uptake by plants compared to using either of them alone. A better understanding how the two microorganism groups and Si interact is crucial to preserving soil fertility and improving the economic and environmental sustainability of crop production in P deficient soils. This review summarizes and discusses the current knowledge concerning the interactions among AMF, PSB, and Si in enhancing P availability and its uptake by plants in sustainable agriculture.

Silicon Amendment Enhances Agronomic Efficiency of Nitrogen Fertilization in Maize and Wheat Crops under Tropical Conditions

Sustainable management strategies are needed to improve agronomic efficiency and cereal yield production under harsh abiotic climatic conditions such as in tropical Savannah. Under these environments, field-grown crops are usually exposed to drought and high temperature conditions. Silicon (Si) application could be a useful and sustainable strategy to enhance agronomic N use efficiency, leading to better cereal development. This study was developed to explore the effect of Si application as a soil amendment source (Ca and Mg silicate) associated with N levels applied in a side-dressing (control, low, medium and high N levels) on maize and wheat development, N uptake, agronomic efficiency and grain yield. The field experiments were carried out during four cropping seasons, using two soil amendment sources (Ca and Mg silicate and dolomitic limestone) and four N levels (0, 50, 100 and 200 kg N ha-1). The following evaluations were performed in maize and wheat crops: the shoots and roots biomass, total N, N-NO3-, N-NH4+ and Si accumulation in the shoots, roots and grain tissue, leaf chlorophyll index, grain yield and agronomic efficiency. The silicon amendment application enhanced leaf chlorophyll index, agronomic efficiency and N-uptake in maize and wheat plants, benefiting shoots and roots development and leading to a higher grain yield (an increase of 5.2 and 7.6%, respectively). It would be possible to reduce N fertilization in maize from 185-180 to 100 kg N ha-1 while maintaining similar grain yield with Si application. Additionally, Si application would reduce N fertilization in wheat from 195-200 to 100 kg N ha-1. Silicon application could be a key technology for improving plant-soil N-management, especially in Si accumulator crops, leading to a more sustainable cereal production under tropical conditions.

Synergistic effects of bast fiber seedling film and nano-silicon fertilizer to increase the lodging resistance and yield of rice

The use of bast fiber film can improve rice seedling quality, and nano-silicon fertilizer can increase rice yields. This study aimed to compare the effects of using bast fiber film, nano-silicon fertilizer, and both treatments on rice yield and lodging resistance. A 2-year field experiment was conducted in 2017 and 2018, in Liaoning, China. The experiment comprised a control (no-bast fiber film, no nano-silicon fertilizer; CK), and three treatments: seedlings cultivated with bast film (FM), single nano-silicon fertilization (SF), and bast fiber film seedlings + nano-silicon fertilization (FM + SF). The japonica rice (Oryza sativa L.) cultivar Liaojing 371 was used. Compared with the plants in CK, those in the FM treatment showed greater average root diameter, root volume and root dry weight. The SF treatment increased the single stem flexural strength, increased the contents of silicon, lignin, and cellulose in the rice plant stalk, and reduced the lodging index, thereby increasing lodging resistance. The SF treatment resulted in increased leaf chlorophyll content at late growth stage and a higher net photosynthetic rate, which increased plant dry matter accumulation. In the FM + SF treatment, plant growth was enhanced during the whole growth period, which resulted in an increased number of effective panicles and an increased grain yield. The results show that the combination of FM and SF synergistically improves rice lodging resistance and grain yield. This low-cost, high-efficiency system is of great significance for improving the stability and lodging resistance of rice plants, thereby increasing yields.

Effects of CO2 and temperature on phytolith dissolution

Phytoliths, silica structures derived from plant residues in silicon (Si)-accumulating plant species, have recently been recognized as a sink and source of nutrients and a hosting phase for carbon sequestration in soil. While the solubility of phytoliths in relation to their respective nature and solution chemistry has been intensively studied, the combined effects of CO₂ and temperature, two highly variable parameters in soil, have not been fully understood. We hypothesized that changes in CO₂ and temperature may affect the dissolution rate, thereby resizing the soil phytolith pool. Rice straw phytoliths were obtained from either open burning or controlled heating of straw from 300 to 900 °C and used to determine their batch incubation kinetics in a closed chamber at CO₂ concentrations of 0 to 15% vol. and a temperature range of 20 to 50 °C for six days. The results revealed a contrasting effect in which temperature and CO₂ were correspondingly found to accelerate or decelerate the dissolution rate of phytoliths. Under the most dissimilar conditions, i.e., 0% vol. CO₂ and 50 °C and 15% vol. CO₂ and 20 °C, the discrepancy in solubility was approximately six-fold, indicating a high vulnerability of phytoliths to CO₂ and temperature changes. This finding also suggests that the soil phytolith pool can be diminished in the case of either increasing soil temperature or decreasing CO₂ flux. Calculations based on these data revealed that the dissolution rate of phytoliths could be increased by an average of 4.5 to 7.3% for each 1 °C increase in temperature. This finding suggests a possible impact of current global warming on the global biogenic silica pool, and more insight into the relationship between this pool and climate change is, therefore, necessary to maintain the function of the phytolith phase in soil.