The research, led by Jannatul Ferdous and colleagues at the Hawkesbury Institute for the Environment at Western Sydney University, set out to resolve a long-standing inconsistency in the plant science literature. Numerous studies have reported that silicon alleviates salinity stress in crops ranging from rice and tomato to maize and wheat, yet others have found the benefits negligible or absent. The team suspected that much of this confusion stemmed from experimental designs that tested only a single silicon source and a single genotype, making it impossible to separate the effects of silicon chemistry from those of plant genetics.

To untangle these variables, the researchers ran a fully factorial glasshouse experiment of unusual scale. Ten commercially relevant Australian wheat cultivars, including Ballista, Calibre, Catapult, Coolah, Coota, EGA Gregory, Elmore CL Plus, Mace, Scepter and Sunflex, were grown under saline and non-saline conditions and treated with one of three silicon regimes: a granular amorphous silica derived from diatomaceous earth, a liquid formulation of the same amorphous silica, and a liquid potassium silicate solution. Each silicon treatment was paired with an appropriate matched control, including a potassium chloride control to isolate the effect of silicon from that of potassium alone. With ten replicates per combination, the experiment encompassed a total of 1,000 plants.

The baseline damage inflicted by salt was substantial and consistent with the broader literature. Salinity reduced root biomass by an average of 35.6 percent and shoot biomass by 25.6 percent across the ten cultivars under silicon-free conditions, though the severity varied considerably between genotypes. Salt stress imposes a double burden on plants: it makes water harder to extract from the soil, creating an osmotic drought, and it allows sodium ions to accumulate in shoots, where they disrupt nutrient uptake, enzyme function and cellular ion balance. Sodium is considered the dominant culprit in cereals, which is why strategies that limit its movement into above-ground tissue are so valuable.

What happened next was striking. Where silicon worked, it worked spectacularly. Root biomass responses under salinity ranged from a 51.4 percent decline in Ballista supplied with granular amorphous silica to a 113.8 percent gain in Scepter supplied with liquid amorphous silica. Shoot responses were even more dramatic, spanning from a 71.7 percent reduction in Coolah with granular silicon to a 133 percent increase in EGA Gregory receiving the liquid formulation. In other words, the same element, applied to the same species under the same stress, could either nearly double a plant’s growth or actively worsen its decline, depending entirely on the cultivar and the delivery form.

Across the board, liquid silicon formulations proved the most reliable performers. Liquid amorphous silica produced the clearest benefits under both saline and non-saline conditions, boosting root and shoot biomass by an average of 29.6 percent and 21.1 percent respectively under non-saline conditions, while liquid potassium silicate delivered moderate but consistent root protection. The granular form, by contrast, was erratic, producing strong gains in some cultivars such as Scepter but pronounced negative effects in others, including Coolah and Ballista. The researchers attribute this pattern to release kinetics: soluble silicates are immediately bioavailable to plant roots, whereas granular amorphous sources must dissolve slowly before plants can access them. In a short-term experiment where salt stress was imposed after establishment, that timing mismatch appears decisive, and it hints that granular products might perform better in field settings where gradual dissolution aligns with crop development.

The mechanistic heart of the study lies in its sodium measurements. The team quantified foliar silicon and sodium concentrations using energy-dispersive X-ray fluorescence, validating the sodium readings against a conventional microwave digestion and flame photometry method in a targeted subset of 80 samples, with strong agreement between the two approaches. In EGA Gregory, the cultivar that showed the strongest silicon-mediated rescue of shoot growth under salinity, liquid amorphous silica slashed shoot sodium concentrations from 8.07 to 2.51 milligrams per gram of dry weight. In Calibre, a cultivar that derived little biomass benefit from silicon, no significant sodium reduction was detected. Across all ten cultivars, five showed significant negative correlations between foliar silicon and sodium, meaning that plants accumulating more silicon tended to accumulate less sodium.

These findings support an increasingly refined model of how silicon protects plants from salt. Rather than acting as a simple growth stimulant, silicon appears to function as a modulator of ion homeostasis. Silicon deposited in the root apoplast is thought to reinforce endodermal barriers through suberisation and lignification, reducing the bypass flow of sodium that would otherwise stream unchecked into the shoot. Related work in maize has shown that silicon up-regulates sodium efflux genes such as SOS1 and SOS2 while promoting sequestration of sodium into leaf vacuoles, effectively shielding the photosynthetic machinery from ionic toxicity. Intriguingly, the study found that total foliar silicon concentration did not predict biomass recovery, suggesting that the functional benefit depends on where silicon is deposited, particularly in root barriers, rather than how much accumulates in bulk tissue.

Perhaps the most consequential discovery is the decoupling of salinity sensitivity from silicon responsiveness. Cultivars that were naturally more salt-tolerant did not necessarily gain more from silicon supplementation, and the two traits appear to be governed by largely independent genetics. The authors highlight a particularly instructive comparison: Coolah was directly derived from EGA Gregory, yet the two cultivars responded in opposite directions, with EGA Gregory benefiting substantially from silicon while Coolah was unaffected or even harmed. For breeders and agronomists, this means that blanket recommendations for silicon fertilisation are unlikely to succeed. Instead, the study points toward an integrated strategy in which cultivar selection is paired with targeted, genotype-specific silicon management.

The implications extend well beyond wheat. Silicon is abundant, non-toxic and environmentally benign, making it an attractive alternative to approaches with heavier trade-offs, such as costly irrigation schemes, slow breeding pipelines or osmo-protectants that are impractical at scale, especially for resource-poor farmers. Yet the study also tempers enthusiasm with realism. Liquid silicates are more expensive than granular products, and their economic viability will depend on whether the yield protection they provide under salinity justifies the input costs. What the research delivers is something the field has lacked: a mechanistic and predictive framework for when silicon fertilisation will actually work. By linking sodium exclusion to biomass rescue, and by exposing the decisive roles of genotype and formulation, the study transforms silicon from a folk remedy of uncertain reliability into a precision tool, one that could help farmers coax productive harvests from soils that salt has claimed.

Subject of Research: Silicon-mediated alleviation of salinity stress in wheat through reduced sodium accumulation

Article Title: Silicon-mediated alleviation of salinity stress in wheat is linked to reduced sodium accumulation but depends on cultivar and silicon source

Article References: Ferdous, J., Rowe, R., Ning, K., Chen, Z.-H., Tissue, D. T., & Johnson, S. N. (2026). Silicon-mediated alleviation of salinity stress in wheat is linked to reduced sodium accumulation but depends on cultivar and silicon source. Plant and Soil. https://doi.org/10.1007/s11104-026-09104-3

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09104-3

Keywords: wheat, silicon, salinity stress, sodium accumulation, plant physiology, abiotic stress, soil science, crop resilience, amorphous silica, potassium silicate, cultivar variation, ion homeostasis

The team, led by Cyrill Joël Ngally Sabouang and Jean Aimé Mbey and drawn from the University of Yaoundé I, the University of Bamenda and the University of Ngaoundere, started with kaolin clay from the Mayouom locality of Cameroon. Kaolinite, the dominant mineral in this clay, is a layered silicate made of one tetrahedral silica sheet stacked on one octahedral alumina sheet, with an ideal formula of Al2Si2O5(OH)4. That structure means kaolinite contains roughly 46.5 percent silicon dioxide by mass, making it an attractive and abundant feedstock for producing amorphous silica, the reactive form of the material prized for adsorption applications. Prior to synthesis, the raw clay was wet-sieved at 45 micrometers, dried, and characterized as containing more than 80 weight percent kaolinite with good structural organization.

The first critical transformation was thermal. Heating the kaolin in a muffle furnace to 650 degrees Celsius at 5 degrees per minute, holding for one hour, and then cooling converted the crystalline kaolinite into amorphous metakaolinite. X-ray diffraction confirmed the change: the characteristic kaolinite reflection at 7.16 angstroms vanished, replaced by a broad diffraction halo between 20 and 35 degrees two-theta that signals a disordered, glass-like atomic arrangement. Infrared spectroscopy told the same story from a different angle. The sharp O-H stretching bands of kaolinite at 3691 and 3620 inverse centimeters disappeared after calcination, evidence that the structural hydroxyls had been driven off and the crystal lattice disrupted. Thermal analysis added a third confirmation, showing the expected dehydroxylation event near 546 degrees with a 10.8 percent mass loss, and a later exothermic event near 1013 degrees marking the onset of mullite formation if the material were heated further.

Before gel synthesis, the metakaolin was purified by dispersing it in excess 3 molar hydrochloric acid for one hour under constant stirring, a treatment that dissolves metallic impurities such as iron oxide and calcium or magnesium compounds. After decantation and repeated washing with distilled water—until a silver nitrate test confirmed the supernatant was free of chloride ions—the cleaned solid was dried and stored airtight. The synthesis itself followed a classic sol-gel route: batches of 5, 10, 15 and 20 grams of treated metakaolin were dispersed in 100 milliliters of 8 molar sodium hydroxide, stirred for 20 minutes, and left for 24 hours. During this alkaline digestion, hydroxide ions attack the silicate network of the metakaolin, dissolving silicon species into solution as sodium silicate. The supernatant was filtered off, and the pH was dropped to 3 with hydrochloric acid, triggering the hydrolysis and condensation reactions that precipitate silica gel. The gels were collected by centrifugation, dried at room temperature, and labeled GS1:20 through GS4:20 according to their clay-to-solution ratios.

X-ray diffraction of the finished gels revealed a broad amorphous silica halo between 15 and 40 degrees two-theta in every sample, but the details differed in ways that turned out to be scientifically revealing. All gels contained crystalline reflections from halite—ordinary sodium chloride—formed either when excess sodium hydroxide reacted with the hydrochloric acid during the pH adjustment step, or when sodium silicate was directly neutralized during precipitation. Crucially, the intensity of the halite peak at 2.82 angstroms shrank as the metakaolin fraction increased, indicating that the dominant source of salt contamination was leftover alkali rather than the silicate itself. The researchers suggest that a post-centrifugation washing step could strip out much of this by-product, and note that the brief 3-minute spin at 2000 rpm may have left enough liquid in the cake for salt to precipitate during drying.

The highest metakaolin loading, GS4:20, produced the most distinctive mineralogy. Its halite peaks were faintest, its amorphous halo strongest, and its pattern showed traces of hydroxysodalite, an ordered aluminosilicate framework that the authors interpret as the beginning of crystallization from the silica oligomers in the gel. They attribute this to the mixture approaching a stoichiometric balance, leaving less free sodium available to form salt. The halo intensity ranked GS3:20 below GS2:20, below GS1:20, below GS4:20, consistent with more silica gel forming as more metakaolin was dissolved into the alkali.

Infrared spectroscopy then exposed how the ratio sculpted the gel’s molecular structure. All gels showed a broad band near 3385 inverse centimeters from O-H stretching of terminal silanol groups and adsorbed water, a Si-OH vibration near 930, an H-O-H bending band near 1640 from physically adsorbed water, and Si-O-Si stretching modes near 1010, 780 and 420. In GS4:20, the silanol and water bands were strongest, pointing to a network built from short oligomeric chains. Shorter chains mean more chain ends, and more chain ends mean more exposed hydroxyl groups available to hydrogen-bond with water molecules—an outcome directly beneficial for a desiccant. By contrast, gels made with less metakaolin, such as GS1:20, showed enhanced Si-O-Si bands without equivalent silanol signals, indicating longer polymer chains with fewer terminal hydroxyls, and trapped structural water instead.

Thermal analysis corroborated the spectroscopic picture. All samples lost physisorbed water below 100 degrees, but the temperature of that event increased in the order GS2:20, GS3:20, GS1:20, GS4:20, implying progressively stronger water-gel bonding forces. Only GS1:20 and GS2:20 showed additional water evaporation between 100 and 210 degrees, attributed to water trapped inside the growing silica network when more effective dissolution allowed optimal chain growth. Total mass loss rose with metakaolin content, again consistent with short-chain, hydroxyl-rich structures adsorbing more water. A thermal event near 800 degrees marked halite melting, weakest in GS4:20, matching the diffraction evidence of minimal salt in that sample.

The overall mechanistic narrative is one of competing interactions. When metakaolin is scarce, the abundant hydroxide solution interacts strongly and effectively with each silicate unit, dissolving species thoroughly and allowing silica particles to grow into extended chains that incorporate structural water. When metakaolin is plentiful, solid-solid interactions between particles stabilize them and limit their contact with the alkali, curtailing particle growth and freezing short oligomers rich in terminal hydroxyls into the network. Meanwhile, excess sodium hydroxide left over after sodium silicate formation reacts with the hydrochloric acid added for precipitation, generating the halite by-product that contaminates low-ratio gels.

The authors are careful to flag a limitation: the study did not specify sodium-to-silicon ratios in a normalized way, which may restrict how directly the conclusions transfer to metakaolins from other natural sources with different purities and reactivities. Even so, the practical takeaway is striking. By simply adjusting how much clay is loaded into the alkali bath, a producer can bias the product toward either long-chain gels with structural water or short-chain gels dense with adsorption-ready hydroxyl groups—tunable moisture retention from one of the cheapest raw materials on Earth. For a material that quietly protects everything from medicines to microchips against humidity, that kind of formulation control, derived from Cameroonian kaolin and conventional laboratory reagents, could reshape how low-cost desiccants are designed.

Subject of Research: Effect of metakaolin mass fraction in sodium hydroxide on sol-gel silica gel structure and water retention

Article Title: Influence of the metakaolin mass fraction in sodium hydroxide solution on the synthesis of silica gel from metakaolin

Article References: Influence of the metakaolin mass fraction in sodium hydroxide solution on the synthesis of silica gel from metakaolin. (n.d.). https://doi.org/10.1007/s44508-026-00015-w

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00015-w

Keywords: metakaolin, silica gel, sol-gel, kaolinite, sodium hydroxide, amorphous silica, X-ray diffraction, FTIR, thermal analysis, desiccant, hydroxysodalite, materials chemistry