Heavy metal contamination from industrial discharge, wastewater irrigation, and excessive fertilizer use is a growing environmental concern in agricultural soils, severely impacting crop productivity. Cadmium (Cd) and chromium (Cr) are particularly toxic, with approximately 137,000 sites in Europe and 11% of agricultural soils in China contaminated. Maize (Zea mays L.), a globally important cereal crop, is highly susceptible to these toxic metals, which disrupt nutrient uptake, damage root structures, and induce oxidative stress, inhibiting plant growth and development. A recent study published in Scientific Reports explores a cost-effective and sustainable mitigation strategy: utilizing spent mushroom substrate (SMS) biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More.

The research investigated the effectiveness of SMS biochar at varying application rates (0, 50, 100, 150, and 200 grams of biochar per kilogram of soil, referred to as 0B, 50B, 100B, 150B, and 200B) in mitigating Cd and Cr toxicity in maize plants. The biochar, prepared at 500°C for 2 hours, possessed a surface area of 5.10 m²/g and a pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More of 8.15.

The results showed that the highest application rate, 200B, significantly improved maize growth and resilience under Cd and Cr stress. This treatment led to a 26.1% increase in plant height (to 89.9 cm) compared to the control group (71.3 cm). Root dry weight saw an even more dramatic increase of 99.7% at 200B (6.43 g) compared to the control (3.07 g). Grain yield was also substantially enhanced, increasing by 98.2% at 200B (213 g per pot) compared to the control (103.33 g per pot). The number of grains per cob at 200B showed a 177.6% increase over the control, reaching 310 grains. Biological yield also increased by 81.7% at 200B (450.53 g per pot) from the control (248 g per pot).

Beyond physical growth, SMS biochar also improved biochemical resilience. Chlorophyll content increased by 50% at 200B (49.6 SPAD units) compared to the control (33.07 SPAD units). This is significant because heavy metals can adversely affect chloroplast structure and decrease photosynthetic efficiency. The activities of key antioxidant enzymes, peroxidase (POD) and superoxide dismutase (SOD), were enhanced. At 200B, POD activity increased by 107.1% (to 94.34 µg/g FW), and SOD activity increased by 104.1% (to 68.10 µg/g FW). Conversely, the activities of ascorbate peroxidase (APX) and levels of reduced glutathione (GSH), ascorbic acid (AsA), proline, and phenolics, which typically decline under stress, were decreased by biochar application, possibly due to nutrient immobilization or altered metal bioavailability.

Furthermore, SMS biochar significantly reduced the accumulation and translocation of Cd and Cr in maize plant parts. At 200B, root Cd concentration decreased by 73.7% (to 6.75 µg/g), shoot Cd by 88.6% (to 2.42 µg/g), and grain Cd by a remarkable 94.2% (to 1.06 µg/g). Similarly, root Cr decreased by 75.0% (to 5.33 µg/g), shoot Cr by 85.8% (to 2.40 µg/g), and grain Cr by 91.4% (to 1.07 µg/g). The translocation factor (TF) of Cd from root to shoot decreased by 43.3% at 200B, and from shoot to grain by 49.2%. For Cr, the TF from root to shoot decreased by 39.8%, and from shoot to grain by 56.8%.

The study concludes that SMS biochar, particularly at a 200 g/kg soil application rate, holds promising potential as a sustainable amendment for mitigating Cd and Cr stress in maize plants. Its mechanisms include immobilizing heavy metals through precipitation, electrostatic attraction, and complex formation, increasing soil pH, and enhancing soil properties like cation exchange capacity, organic matter content, and microbial diversity. Further extensive field investigations are suggested to validate its effectiveness as a primary solution for agricultural application.

Source: Dawar, K., Khan, A. U., Al-Mutairi, M., Alotaibi, M. O., Mian, I. A., Muhammad, A., Alam, S. S., Shoaib, S., & Ghoneim, A. M. (2025). Utilizing spent mushroom substrate biochar to improve Zea mays L. growth and biochemical resilience against cadmium and chromium toxicity. Scientific Reports, 15(1), 17511.