Effect of silica nanoparticles on microbial biomass and silica availability in maize rhizosphere

Advances in silica nanoparticles for agricultural applications and biosynthesis

Nanotechnology has emerged as a revolutionary force in modern agriculture, opening new avenues for crop enhancement and sustainable farming practices. This review systematically evaluates the roles of silica nanoparticles (SiO2 NPs) in agricultural applications, with particular emphasis on their biosynthesis pathways and functional mechanisms. SiO2 NPs have demonstrated considerable potential to enhance crop resilience against both biotic (pathogens, pests) and abiotic (heavy metals, salinity, drought) stresses through phytohormonal regulation, defense gene activation, and metabolic modulation. As nanocarriers, these particles enhance pesticide and fertilizer delivery accuracy, reduce environmental contamination, and promote plant growth. Biosynthesis methods of SiO2 NPs range from conventional physical-chemical techniques to eco-friendly green approaches, including the utilization of biological cells/extracts, natural biomaterials, and peptide templates. Although green synthesis offers sustainability advantages, the agricultural adoption of SiO2 NPs faces critical challenges, such as insufficient understanding of their long-term environmental persistence and ecotoxicological impacts, high production costs related to green synthesis, and incomplete regulatory frameworks. Addressing these challenges is essential to enable their broader use in agriculture.

LPDE biodegradation promoted by a novel additive based on silica nanoparticles: Structural, microbial and ecotoxicological characterization

This study developed a biodegrading additive based on nanosilica and modified by cellulase enzyme in the presence of citric acid and sodium citrate. The additive was tested as a facilitator for biodegradation of the commercial low-density polyethylene (LDPE) in soil. Enzyme immobilization was confirmed by enzymatic assays. Moreover, additive and nanocomposites were characterized by spectroscopic and microscopic techniques. To assess the role of additive in biodegradation, CO2 production in soil was measured at 30 °C for 83 days. Biodegraded nanocomposites were cultivated to isolate possible LDPE-biodegrading microorganisms. Ecotoxicity of the studied materials was evaluated on cucumber (Cucumis sativus L.). CO2 production from LDPE/additive sample was similar to the starch (1055 ± 14 mg and 1078 ± 28 mg, respectively), and higher than pure LDPE (882 ± 34 mg) and LDPE/nanosilica (992 ± 30 mg). Although the presence of LDPE/nanosilica and LDPE/additive led to root length reduction of 24.3 ± 2.3% compared to the control (soil), the accumulation of root biomass was not affected. Furthermore, the nanocomposites did not cause harmful effects on seedling growth. Nine microbial isolates were recovered from biodegraded samples and identified by molecular techniques. It was demonstrated for the first time the LDPE biodegradation potential by four bacterial isolates (Bacillus safensis FO-36b, Lysinibacillus capsici, Bacillus albus N35-10-2 and Bacillus paranthracis Mn5) and two fungal isolates (Cladosporium halotolerans clone EF_526 and Cladosporium sp. MV-2018B isolate MLT-27). Our study sheds light on the biodegradation of commercial LDPE by soil microorganisms using a novel LDPE-biodegrading additive nanocomposite.

Facade eluates affect active and total soil microbiome

The application of biocides in building materials has become a prevalent practice to mitigate the growth of microorganisms such as algae, fungi, and bacteria on the façades. These can leach out from the material and reach the nearby soil environment. This study aimed to characterize the effect of façade eluates generated within different leaching experiments on total and metabolic active soil microbial community composition and functions. Façade eluates were produced by immersion testing DIN EN 16105 and a natural weathering experiment. Afterward, soil microcosms were treated with the respective façade eluate and incubated for 29 days. Subsequently, the active and total soil microbial community compositions were investigated. Fungal internal transcribed spacer region gene and bacterial 16S rRNA gene were sequenced for active (bromodeoxyuridine labeled DNA) microbial community and total community. Façade eluates reduced total bacterial and fungal gene copy numbers. Overall, active bacterial and fungal richness was reduced and altered in community composition in comparison to the total richness and composition, respectively. Façade eluates retrieved of façade samples without biocides did alter the soil microbial communities to the same extent as façade eluates with biocides. Additionally, members of the active microbiome that benefit from the presence of façade eluates and omitted ones could be identified. Our result demonstrated that façade eluates affect active and total soil microbial community composition and function regardless of the leaching procedure and biocides addition.

Enhancing Maize Yield and Quality with Metal-Based Nanoparticles without Translocation Risks: A Brief Field Study

Our previous studies have shown physiological and yield intensification of selected crops with the application of nanoparticles (NPs). However, the impact on the quantitative, qualitative, and yield parameters of maize (Zea mays L.) in field conditions remains highly debated. This study aimed to evaluate the effects of zinc oxide (ZnO-NPs), gold NPs anchored to meso-biosilica (Au-NP-bioSi), and titanium dioxide (TiO2-NPs) as biological stimulants under field conditions during the vegetation season of 2021 in the Central European region. The study assessed the effects on the number of plants, yield, yield components, and nutritional quality, including mineral nutrients, starch, and crude protein levels. The potential translocation of these chemically-physically stable NPs, which could pose a hazard, was also investigated. The results indicate that Au-NP-bioSi and ZnO-NPs-treatments were the most beneficial for yield and yield components at a statistically significant level. Mineral nutrient outcomes were varied, with the NP-free variant performing the best for phosphorus-levels, while Au-NP-bioSi and ZnO-NPs were optimal for crude protein. Starch content was comparable across the TiO2-NPs, Au-NP-bioSi, and control variants. Importantly, we observed no hazardous translocation of NPs or negative impacts on maize grain quality. This supports the hypothesis that NPs can serve as an effective tool for precise and sustainable agriculture.

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Nanoparticle applications in agriculture: overview and response of plant-associated microorganisms

Globally, food security has become a critical concern due to the rise in human population and the current climate change crisis. Usage of conventional agrochemicals to maximize crop yields has resulted in the degradation of fertile soil, environmental pollution as well as human and agroecosystem health risks. Nanotechnology in agriculture is a fast-emerging and new area of research explored to improve crop productivity and nutrient-use efficiency using nano-sized agrochemicals at lower doses than conventional agrochemicals. Nanoparticles in agriculture are applied as nanofertilizers and/or nanopesticides. Positive results have been observed in terms of plant growth when using nano-based agricultural amendments. However, their continuous application may have adverse effects on plant-associated rhizospheric and endospheric microorganisms which often play a crucial role in plant growth, nutrient uptake, and disease prevention. While research shows that the application of nanoparticles has the potential to improve plant growth and yield, their effect on the diversity and function of plant-associated microorganisms remains under-explored. This review provides an overview of plant-associated microorganisms and their functions. Additionally, it highlights the response of plant-associated microorganisms to nanoparticle application and provides insight into areas of research required to promote sustainable and precision agricultural practices that incorporate nanofertilizers and nanopesticides.

Amorphous silica nanoparticles and the human gut microbiota: a relationship with multiple implications

Amorphous silica nanoparticles (ASNP) are among the nanomaterials that are produced in large quantities. ASNP have been present for a long time in several fast-moving consumer products, several of which imply exposure of the gastrointestinal tract, such as toothpastes, food additives, drug excipients, and carriers. Consolidated use and experimental evidence have consistently pointed to the very low acute toxicity and limited absorption of ASNP. However, slow absorption implies prolonged exposure of the intestinal epithelium to ASNP, with documented effects on intestinal permeability and immune gut homeostasis. These effects could explain the hepatic toxicity observed after oral administration of ASNP in animals. More recently, the role of microbiota in these and other ASNP effects has attracted increasing interest in parallel with the recognition of the role of microbiota in a variety of conditions. Although evidence for nanomaterial effects on microbiota is particularly abundant for materials endowed with bactericidal activities, a growing body of recent experimental data indicates that ASNPs also modify microbiota. The implications of these effects are recounted in this contribution, along with a discussion of the more important open issues and recommendations for future research.

Unveiling the Potential of Bioinoculants and Nanoparticles in Sustainable Agriculture for Enhanced Plant Growth and Food Security

The increasing public concern over the negative impacts of chemical fertilizers and pesticides on food security and sustainability has led to exploring innovative methods that offer both environmental and agricultural benefits. One such innovative approach is using plant-growth-promoting bioinoculants that involve bacteria, fungi, and algae. These living microorganisms are applied to soil, seeds, or plant surfaces and can enhance plant development by increasing nutrient availability and defense against plant pathogens. However, the application of biofertilizers in the field faced many challenges and required conjunction with innovative delivering approaches. Nanotechnology has gained significant attention in recent years due to its numerous applications in various fields, such as medicine, drug development, catalysis, energy, and materials. Nanoparticles with small sizes and large surface areas (1-100 nm) have numerous potential functions. In sustainable agriculture, the development of nanochemicals has shown promise as agents for plant growth, fertilizers, and pesticides. The use of nanomaterials is being considered as a solution to control plant pests, including insects, fungi, and weeds. In the food industry, nanoparticles are used as antimicrobial agents in food packaging, with silver nanomaterials being particularly interesting. However, many nanoparticles (Ag, Fe, Cu, Si, Al, Zn, ZnO, TiO2, CeO2, Al2O3, and carbon nanotubes) have been reported to negatively affect plant growth. This review focuses on the effects of nanoparticles on beneficial plant bacteria and their ability to promote plant growth. Implementing novel sustainable strategies in agriculture, biofertilizers, and nanoparticles could be a promising solution to achieve sustainable food production while reducing the negative environmental impacts.

Effects of silicon nanoparticles and conventional Si amendments on growth and nutrient accumulation by maize (Zea mays L.) grown in saline-sodic soil

Salinity is one of the major abiotic stresses in arid and semiarid climates which threatens the food security of the world. Present study had been designed to assess the efficacy of different abiogenic sources of silicon (Si) to mitigate the salinity stress on maize crop grown on salt-affected soil. Abiogenic sources of Si including silicic acid (SA), sodium silicate (Na-Si), potassium silicate (K-Si), and nanoparticles of silicon (NPs-Si) were applied in saline-sodic soil. Two consecutive maize crops with different seasons were harvested to evaluate the growth response of maize under salinity stress. Post-harvest soil analysis showed a significant decrease in soil electrical conductivity of soil paste extract (EC_e) (-23.0%), sodium adsorption ratio (SAR) (-47.7%) and pH of soil saturated paste (pHs) (-9.5%) by comparing with salt-affected control. Results revealed that the maximum root dry weight was recorded in maize1 by the application of NPs-Si (149.3%) and maize2 (88.6%) over control. The maximum shoot dry weight was observed by the application of NPs-Si in maize1 (42.0%) and maize2 (7.4%) by comparing with control treatment. The physiological parameters like chlorophyll contents (52.5%), photosynthetic rate (84.6%), transpiration (100.2%), stomatal conductance (50.5%), and internal CO₂ concentration (61.6%) were increased by NPs-Si in the maize1 crop when compared with the control treatment. The application of an abiogenic source (NPs-Si) of Si significantly increased the concentration of phosphorus (P) in roots (223.4%), shoots (22.3%), and cobs (130.3%) of the first maize crop. The current study concluded that the application of NPs-Si and K-Si improved the plant growth by increasing the availability of nutrients like P and potassium (K), physiological attributes, and by reducing the salts stress and cationic ratios in maize after maize crop rotation..

Elicitation of Bacillus cereus-Amazcala (B.c-A) with SiO2 Nanoparticles Improves Its Role as a Plant Growth-Promoting Bacteria (PGPB) in Chili Pepper Plants

Agriculture needs to decrease the use of agrochemicals due to their high toxicity and adopt new strategies to achieve sustainable food production. Therefore, nanoparticles (NPs) and plant growth-promoting bacteria (PGPB) have been proposed as viable strategies to obtain better crop yields with less environmental impact. Here, we describe the effect of silica nanoparticles (SiO₂-NPs) on survival, antioxidant enzymatic activity, phosphate solubilization capacity, and gibberellin production of Bacillus cereus-Amazcala (B.c-A). Moreover, the effect of the co-application of SiO₂-NPs and B.c-A on seed germination, physiological characteristics, and antioxidant enzymatic activity of chili pepper plants was investigated under greenhouse conditions. The results indicated that SiO₂-NPs at 100 ppm enhanced the role of B.c-A as PGPB by increasing its phosphate solubilization capacity and the production of GA7. Moreover, B.c-A catalase (CAT) and superoxide dismutase (SOD) activities were increased with SiO₂-NPs 100 ppm treatment, indicating that SiO₂-NPs act as a eustressor, inducing defense-related responses. The co-application of SiO₂-NPs 100 ppm and B.c-A improved chili pepper growth. There was an increase in seed germination percentage, plant height, number of leaves, and number and yield of fruits. There was also an increase in CAT and PAL activities in chili pepper plants, indicating that bacteria-NP treatment induces plant immunity.

Recycling of silicon-rich agro-wastes by their combined application with phosphate solubilizing microbe to solubilize the native soil phosphorus in a sub-tropical Alfisol

It is imperative to find suitable strategies to utilize the native soil phosphorus (P), as natural rock phosphate deposits are at a verge of depletion. We explored two such cost-effective and eco-friendly strategies for native soil P solubilization: silicon (Si)-rich agro-wastes (as Si source) and phosphate solubilizing microorganism (PSM). An incubation study was conducted in a sub-tropical Alfisol for 90 days at 25 °C under field capacity moisture. A factorial completely randomized design with 3 factors, namely: Si sources (three levels: sugarcane bagasse ash, rice husk ash, and corn cob ash), PSM (two levels: without PSM, and with PSM); and Si doses [three levels: no Si (Si₀), 125 (Si₁₂₅) and 250 (Si₂₅₀) mg Si kg^-1 soil] was followed. The PSM increased solution P and soluble Si level by ∼22.2 and 1.88%, respectively, over no PSM; whereas, Si₁₂₅ and Si₂₅₀ increased solution P by ∼60.4 and 77.1%, as well as soluble Si by ∼41.5 and 55.5%, respectively, over Si₀. Also, interaction of PSM × Si doses was found significant (P<0.05). Activities of soil enzymes (dehydrogenase, acid phosphatase) and microbial biomass P also increased significantly both with PSM and Si application. Overall, PSM solubilized ∼4.18 mg kg^-1 of inorganic P and mineralized ∼5.92 mg kg^-1 of organic P; whereas, Si₁₂₅ and Si₂₅₀ solubilized ∼3.85 and 5.72 mg kg^-1 of inorganic P, and mineralized ∼4.15 and 5.37 mg kg^-1 of organic P, respectively. Path analysis revealed that inorganic P majorly contributed to total P solubilization; whereas, soluble and loosely bound, iron bound and aluminium bound P significantly influenced the inorganic P solubilization. Thus, utilization of such wastes as Si sources will not only complement the costly P fertilizers, but also address the waste disposal issue in a sustainable manner.

Application of Silica Nanoparticles in Combination with Two Bacterial Strains Improves the Growth, Antioxidant Capacity and Production of Barley Irrigated with Saline Water in Salt-Affected Soil

Exploitation of low-quality water or irrigation of field crops with saline water in salt-affected soil is a critical worldwide challenge that rigorously influences agricultural productivity and sustainability, especially in arid and semiarid zones with limited freshwater resources. Therefore, we investigated a synergistic amendment strategy for salt-affected soil using a singular and combined application of plant growth-promoting rhizobacteria (PGPR at 950 g ha⁻¹; Azotobacter chroococcum SARS 10 and Pseudomonas koreensis MG209738) and silica nanoparticles (SiNPs) at 500 mg L⁻¹ to mitigate the detrimental impacts of irrigation with saline water on the growth, physiology, and productivity of barley (Hordum vulgare L.), along with soil attributes and nutrient uptake during 2019/2020 and 2020/2021. Our field trials showed that the combined application of PGPR and SiNPs significantly improved the soil physicochemical properties, mainly by reducing the soil exchangeable sodium percentage. Additionally, it considerably enhanced the microbiological counts (i.e., bacteria, azotobacter, and bacillus) and soil enzyme activity (i.e., urease and dehydrogenase) in both growing seasons compared with the control. The combined application of PGPR and SiNPs alleviated the detrimental impacts of saline water on barley plants grown in salt-affected soil compared to the single application of PGPR or SiNPs. The marked improvement was due to the combined application of PGPR and SiNPs, which enhanced the physiological properties (e.g., relative chlorophyll content (SPAD), relative water content (RWC), stomatal conductance, and K/Na ratio), enzyme activity (superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX)), and yield and yield-related traits and nutrient uptake (N, P, and K) of barley plants. Moreover, the Na+ content, hydrogen peroxide (H₂O₂) content, lipid peroxidation (MDA), electrolyte leakage (EL), and proline content were reduced upon the application of PGPR + SiNPs. These results could be important information for cultivating barley and other cereal crops in salt-affected soil under irrigation with saline water.

Silica nanoparticles as novel sustainable approach for plant growth and crop protection

Agriculture crops encounter several biotic and abiotic stresses, including pests, diseases, nutritional deficits, and climate change, which necessitate the development of new agricultural technologies. By developing nano-based fertilizers, insecticides and herbicides, and early disease diagnostics, nanotechnology may help to increase agricultural crop quality and production. The application of silica nanoparticles (SiNPs) may be the solution for increasing the yield to combat the agriculture crisis in the near future. SiNPs have unique physiological properties, such as large surface area, aggregation, reactivity, penetrating ability, size, and structure, which enable them to penetrate plants and regulate their metabolic processes. Pesticide delivery, enhanced nutrition supply, disease management, and higher photosynthetic efficiency and germination rate are all attributed to SiNPs deposition on plant tissue surfaces. SiNPs have been demonstrated to be non-toxic in nature, making them suitable for usage in agriculture. In this regard, the current work provides the most important and contemporary applications of SiNPs in agriculture as well as biogenic and non-biogenic synthetic techniques. As a result, this review summarizes the literature on SiNPs and explores the use of SiNPs in a variety of agricultural disciplines.

Nanofertilizers for agricultural and environmental sustainability

Indiscriminate use of chemical fertilizers in the agricultural production systems to keep pace with the food and nutritional demand of the galloping population had an adverse impact on ecosystem services and environmental quality. Hence, an alternative mechanism is to be developed to enhance farm production and environmental sustainability. A nanohybrid construct like nanofertilizers (NFs) is an excellent alternative to overcome the negative impact of traditional chemical fertilizers. The NFs provide smart nutrient delivery to the plants and proves their efficacy in terms of crop productivity and environmental sustainability over bulky chemical fertilizers. Plants can absorb NFs by foliage or roots depending upon the application methods and properties of the particles. NFs enhance the biotic and abiotic stresses tolerance in plants. It reduces the production cost and mitigates the environmental footprint. Multitude benefits of the NFs open new vistas towards sustainable agriculture and climate change mitigation. Although supra-optimal doses of NFs have a detrimental effect on crop growth, soil health, and environmental outcomes. The extensive release of NFs into the environment and food chain may pose a risk to human health, hence, need careful assessment. Thus, a thorough review on the role of different NFs and their impact on crop growth, productivity, soil, and environmental quality is required, which would be helpful for the research of sustainable agriculture.

Effects of nanofertilizers on soil and plant-associated microbial communities: Emerging trends and perspectives

Modern agricultural practices are relying excessively upon the use of synthetic fertilizers to supply essential nutrients to promote crop productivity. Though useful in the short term, their prolonged and persistent applications are harmful to soil fertility and nutrient dynamics of the rhizospheric microbiome. The application of nanotechnology in form of nanofertilizer provides an innovative, efficient, and eco-friendly alternative to synthetic fertilizers. The nanofertilizers allow a slow and sustained release of nutrients that not only supports plant growth but also conserve the diversity of the beneficial microbiome. Such attributes may help the phytomicrobiome to efficiently mitigate both biotic and abiotic stress conditions. Unfortunately, despite, exceptional efficiency and ease of applications, certain limitations are also associated with the nanofertilizers such as their complicated production process, tenuous transport and dosage-sensitive efficiency. These bottlenecks are causing a delay in the large-scale applications of nanofertilizers in agriculture. This review aims to highlight the current trends and perspectives on the use of nanofertilizers for improving soil fertility with a special focus on their effects on beneficial phyromicrobiome.

The potential of nanomaterials associated with plant growth-promoting bacteria in agriculture

The impacts of chemical fertilizers and pesticides have raised public concerns regarding the sustainability and security of food supplies, prompting the investigation of alternative methods that have combinations of both agricultural and environmental benefits, such as the use of biofertilizers involving microbes. These types of microbial inoculants are living microorganisms that colonize the soil or plant tissues when applied to the soil, seeds, or plant surfaces, facilitating plant nutrient acquisition. They can enhance plant growth by transforming nutrients into a form assimilable by plants and by acting as biological control agents, known as plant growth-promoting bacteria. The potential use of bacteria as biofertilizers in agriculture constitutes an economical and eco-friendly way to reduce the use of chemical fertilizers and pesticides. In this context, nanotechnology has emerged as a new source of quality enrichment for the agricultural sector. The use of nanoparticles can be an effective method to meet the challenges regarding the effectiveness of biofertilizers in natural environments. Given the novel sustainable strategies applied in agricultural systems, this review addresses the effects of nanoparticles on beneficial plant bacteria for promoting plant growth.

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.

Silica Particles Trigger the Exopolysaccharide Production of Harsh Environment Isolates of Growth-Promoting Rhizobacteria and Increase Their Ability to Enhance Wheat Biomass in Drought-Stressed Soils

In coming decades, drought is expected to expand globally owing to increased evaporation and reduced rainfall. Understanding, predicting, and controlling crop plants’ rhizosphere has the potential to manipulate its responses to environmental stress. Our plant growth-promoting rhizobacteria (PGPR) are isolated from a natural laboratory, ‘The Evolution Canyon’, Israel, (EC), from the wild progenitors of cereals, where they have been co-habituating with their hosts for long periods of time. The study revealed that commercial TM50 silica particles (SN) triggered the PGPR production of exopolysaccharides (EPS) containing D-glucuronate (D-GA). The increased EPS content increased the PGPR water-holding capacity (WHC) and osmotic pressure of the biofilm matrix, which led to enhanced plant biomass in drought-stressed growth environments. Light- and cryo-electron- microscopic studies showed that, in the presence of silica (SN) particles, bacterial morphology is changed, indicating that SNs are associated with significant reprogramming in bacteria. The findings encourage the development of large-scale methods for isolate formulation with natural silicas that ensure higher WHC and hyperosmolarity under field conditions. Osmotic pressure involvement of holobiont cohabitation is also discussed.

Silicon Promotes Agronomic Performance in Brassica napus Cultivated under Field Conditions with Two Nitrogen Fertilizer Inputs

To limit the environmental pollution associated with intensive nitrogen (N) fertilizer usage, alternative cultural practices must be considered for crops requiring high N inputs such as rapeseed. In this context, the effects of silicon (Si) supply on the agronomic performance of rapeseed cultivated under field conditions with two N fertilizer levels (60 and 160 kg ha⁻¹) were studied. Results showed that Si supplied in the form of silicic acid (12 kg ha⁻¹) has no effect on the agronomic performance of plants cultivated with the lower N input. In contrast, in plants fertilized with 160 kg N ha⁻¹, Si supply promotes the preservation of green leaves (until the flowering stage) and at harvest stage, increases biomass, yield, and seed micronutrient concentrations (especially cobalt and iron). The agronomic indexes show that the increase in seed yield is related to a better uptake of N from the soil by Si-treated plants, but is not an improvement in N mobilization towards the seeds. This study showed that Si supply combined with high N inputs (160 kg ha⁻¹) improves usage of N fertilizer and yield. The possibility that a Si supply could allow for a reduction in N input without altering the yield of rapeseed is discussed.

Recent Developments on Nanotechnology in Agriculture: Plant Mineral Nutrition, Health, and Interactions with Soil Microflora

Plant mineral nutrition is important for obtaining higher agricultural productivity to meet the future demands of the increasing global human population. It is envisaged that nanotechnology can provide sustainable solutions by replacing traditional bulk fertilizers with their nanoparticulate counterparts possessing superior properties to overcome the current challenges of bioavailability and uptake of minerals, increasing crop yield, reducing fertilizer wastage, and protecting the environment. Recent studies have shown that nanoparticles of essential minerals and nonessential elements affect plant growth, physiology, and development, depending on their size, composition, concentration, and mode of application. The current review includes the recent findings on the positive as well as negative effects that nanofertilizers exert on plants when applied via foliar and soil routes, their effects on plant associated microorganisms, and potential for controlling agricultural pests. This review suggests future research needed for the development of sustained release nanofertilizers for enhancing food production and environmental protection.

Effect of nanozeolite and plant growth promoting rhizobacteria on maize

Plant growth promoting rhizobacteria are key to soil and plant health maintenance. In the present study, two PGPR strains which were identified as Bacillus spp. (accession number KX650178 and KX650179) with nanozeolite (50 ppm) were applied to the seeds in different combinations and tested on growth profile of maize crop. Various growth related parameters, including plant height, leaf area, number of leaves chlorophyll and total protein were positively increased up to twofold by the nanocompound treatment. GC-MS results reveal increase in total phenolic and acid ester compounds after the treatment of nanozeolite and PGPR, which are responsible for stress tolerance mechanism. Soil physicochemical parameters (organic carbon, phosphorous, potassium, ammoniacal nitrogen and nitrate nitrogen) were assessed qualitatively and a shift towards higher amount was observed. Various biochemical parameters of soil health like dehydrogenase, fluorescein diacetate hydrolysis and alkaline phosphatase activity were significantly enhanced up to threefold with the application of different treatments. The results, for the first time, demonstrate successful use of nanozeolite in enhancing growth of Zea mays, under controlled conditions and present a viable alternative to GM crop for ensuring food security.

Titania (TiO2) nanoparticles enhance the performance of growth-promoting rhizobacteria

A novel use of nanotitania (TNs) as agents in the nanointerface interaction between plants and colonization of growth promoting rhizobacteria (PGPR) is presented. The effectiveness of PGPRs is related to the effectiveness of the technology used for their formulation. TNs produced by the Captigel patented SolGel approach, characterized by the transmission and scanning electron microscopy were used for formulation of the harsh environment PGPR strains. Changes in the biomass of wheat seedlings and in the density of single and double inoculants with and without TNs were monitored during two weeks of stress induced by drought salt and by the pathogen Fusarium culmorum. We show that double inoculants with TNs can attach stably to plant roots. Regression analysis indicates that there is a positive interaction between seedling biomass and TN-treated second inoculant colonization. We conclude that TN treatment provides an effectual platform for PGPR rational application via design of root microbial community. Our studies illustrate the importance of considering natural soil nanoparticles for PGPR application and thereby may explain the generally observed inconsistent behavior of PGPRs in the field. These new advancements importantly contribute towards solving food security issues in changing climates. The model systems established here provide a basis for new PGPR nanomaterials research.