Biochar and Silicon Team Up to Shield Triticale from Lead-Tainted Soil

Lead-contaminated farmland is one of the quiet crises of modern agriculture. The toxic metal slips into soils through industrial emissions, mining runoff, irrigation with polluted water, and the long shadow of leaded petrol, and once it is there it does not leave. It stunts roots, scrambles photosynthesis, and can end up in the food chain. Now a team of Iranian researchers has reported that a carefully calibrated pairing of two soil amendments — biochar and silicon — can coax a cereal crop back to vigorous life in soil spiked with a punishing 500 milligrams of lead per kilogram. The catch, they found, is that more is not always better: pushing silicon too high actually reversed the benefits.

The study, conducted at the College of Agriculture and Natural Resources of Darab at Shiraz University, focused on triticale, a hardy hybrid of wheat and rye often grown for grain and forage on marginal land. In a factorial pot experiment arranged in a completely randomized design, the researchers crossed three silicon levels — zero, 200, and 400 milligrams per kilogram of soil — with four biochar treatments: no biochar, sheep manure biochar, rice husk biochar, and municipal waste biochar. Every pot then received the same lead dose, and the plants were left to reveal which combination could best shield them.

The standout result came from sheep manure biochar applied together with 200 milligrams of silicon per kilogram of soil. Compared with untreated control plants, that combination increased leaf weight by a striking 108.3 percent and leaf area by 29.7 percent. Those are not cosmetic gains. Leaf area is the engine of photosynthesis, and a plant that can hold nearly twice the leaf biomass under heavy metal stress has, in effect, rebuilt its solar panels while the poison is still in the ground.

What makes the finding particularly interesting is that the researchers traced the improvement down to the plant’s internal plumbing. Microscopic examination of the leaves showed that the winning treatment enlarged the midrib — the central vascular bundle of the leaf — along with the metaxylem and protoxylem, the water-conducting tissues inside it. Wider xylem vessels mean better hydraulic conductivity, so water and dissolved nutrients can move more freely from root to leaf even when lead is interfering with root function. In effect, the biochar-and-silicon pairing did not just protect the leaf chemically; it physically re-engineered it for better transport under stress.

The biochemical story was just as dramatic. Plants receiving sheep manure biochar with the moderate silicon dose showed a 101.3 percent increase in total chlorophyll content, effectively doubling the pigment machinery that captures light. Carotenoid levels also rose, which matters because carotenoids act as accessory pigments and as quenchers of reactive oxygen species, the destructive molecules that heavy metals generate inside cells. Membrane stability — a key indicator of cellular integrity under stress — improved significantly in the same treatment, suggesting that the combination was keeping lead’s corrosive chemistry at bay at the level of the cell’s outer defenses.

Enzyme activity provided further evidence of a coordinated protective response. Catalase and peroxidase, two of the plant’s frontline antioxidant enzymes, both increased under the optimal treatment. These enzymes dismantle hydrogen peroxide and other reactive oxygen species before they can shred membranes, proteins, and DNA. Elevated catalase and peroxidase activity in the sheep manure biochar plus silicon-200 plants indicates that the treatment did not merely mask stress symptoms but actively strengthened the plant’s oxidative stress mitigation machinery — a hallmark of genuine stress alleviation rather than simple dilution of the toxin.

Dosage, however, proved to be the decisive variable. When the silicon supply was doubled to 400 milligrams per kilogram, the positive effects collapsed. Stomatal area — the size of the microscopic pores that regulate gas exchange and water loss — shrank noticeably at the high dose, a sign that the plants were closing down their exchange surfaces. At that elevated silicon level, rice husk biochar performed particularly poorly, reducing stomatal area by 25.6 percent compared with sheep manure biochar. The authors interpret this as an antagonistic effect: silicon, beneficial in moderation, becomes counterproductive in excess, underscoring that field applications will demand precise dosage optimization rather than generous blanket application.

The downstream consequences for yield were substantial. Plants grown with sheep manure biochar and 200 milligrams of silicon per kilogram grew 19.8 percent taller than controls and accumulated 69.5 percent more total dry matter. Reproductive performance followed suit: the number of grains per spike rose by 65.8 percent, and grain yield climbed by 68.0 percent relative to untreated plants growing in the same lead-laden soil. For a crop like triticale, which is often grown precisely because it tolerates poor conditions, a two-thirds yield recovery under heavy metal stress is a meaningful agronomic margin.

Why did sheep manure biochar outperform its rice husk and municipal waste counterparts? The answer likely lies in feedstock chemistry. Biochars differ enormously in pH, cation exchange capacity, nutrient content, and aromatic carbon structure depending on what they were made from and how they were pyrolyzed. Manure-derived biochars tend to be rich in minerals and alkaline, which can immobilize lead by precipitating it as phosphates and carbonates while simultaneously supplying nutrients. Combined with silicon’s well-documented role in strengthening cell walls, reducing metal translocation, and bolstering antioxidant defenses, the two amendments appear to act synergistically — the biochar locking lead away in the soil while silicon fortifies the plant against whatever it cannot avoid absorbing.

The broader implications reach well beyond a single pot experiment. Heavy metal contamination of agricultural soils threatens food security worldwide, and cheap, locally producible amendments like biochar and silicon fertilizers offer a remediation path that farmers in affected regions could actually afford. The study’s central lesson is one of precision: the synergy between biochar and silicon is real and powerful, but it sits on a knife’s edge of dosage, with the optimal silicon rate doubling chlorophyll and boosting yield by more than two-thirds while an excessive rate constricted stomata and eroded the gains. As the researchers conclude, reclaiming lead-contaminated soils with this pairing is feasible — but only if application rates are tuned with care rather than guesswork.

Subject of Research: Synergistic effects of biochar and silicon fertilization on triticale physiology and yield under lead-contaminated soil

Article Title: Combination of biochar and silicon influenced the leaf structure, phytochemical properties and yield of triticale under lead-contaminated soil

Article References: Bijanzadeh, E., Boostani, H. R., & Najafi-Ghiri, M. (2026). Combination of biochar and silicon influenced the leaf structure, phytochemical properties and yield of triticale under lead-contaminated soil. Discover Sustainability. https://doi.org/10.1007/s43621-026-04899-8

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04899-8

Keywords: biochar, silicon fertilization, lead toxicity, triticale, heavy metal contamination, chlorophyll content, antioxidant enzymes, metaxylem, soil remediation, grain yield, stomata, oxidative stress