The global demand for capsicum, or pepper, has forced many farmers into continuous cropping practices, where the same crop is grown on the same land for decades. While efficient for production, this practice leads to a major agricultural obstacle: the buildup of self-toxic substances, or allelochemicals, secreted by the plant’s own roots. These substances, particularly phenolic acids like ferulic acid, accumulate in the soil and eventually become high enough to suppress plant growth, reduce nutrient absorption, and even cause plant death. Finding a way to clear these “autotoxins” without harming the environment is essential for the long-term sustainability of the vegetable industry. A recent study published in the journal Biochar by Xueyan Zhang and a team of researchers introduces a promising biological solution using modified biochar and specialized enzymes.

To tackle these soil toxins, the researchers turned to horseradish peroxidase, an enzyme known for its high efficiency in breaking down organic pollutants. However, free enzymes are often delicate and easily lose their effectiveness when exposed to fluctuating soil temperatures or 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 levels. To protect the enzyme and enhance its performance, the team created a “carrier” using tobacco stem biochar. By treating the biochar with potassium carbonate, they created a material with an ultra-high surface area and a deep pore structure, providing a perfect home for the enzymes. This modified material, called carbonate-modified biochar, was then loaded with the peroxidase enzymes to create a robust system capable of targeting and neutralizing soil toxins.

The results of the study were highly encouraging, showing that this enzyme-loaded biochar is far more effective than using either biochar or the enzyme alone. Under optimal conditions—a neutral pH and a temperature of 35 degrees Celsius—the system reached a 100 percent removal rate of ferulic acid in just six hours. Furthermore, the material proved its versatility by successfully degrading several other common phenolic acids that plague pepper cultivation, such as cinnamic and vanillic acids. This broad application potential suggests that the technology could be a powerful tool for various types of continuous cropping systems beyond just pepper fields.

Crucially, the study looked beyond just removing the chemicals and examined whether the soil actually became healthier for the plants. When pepper seeds were exposed to untreated ferulic acid solutions, their germination rates dropped by 17 percent, and their roots were significantly shorter. However, once the solution was treated with the enzyme-loaded biochar, the inhibitory effects disappeared, and the seeds grew just as well as those in pure water. Chemical analysis confirmed that the toxic acids were broken down into smaller, less harmful organic molecules through a specialized radical-mediated mechanism.

Another major advantage of this biochar system is its durability and reusability. Because the enzymes are chemically “locked” onto the biochar, they are much more resistant to environmental stress. The study found that even after being used and washed seven times, the material still retained a significant portion of its cleaning power. Additionally, the biochar framework itself acts as a buffer, protecting the enzymes from extreme changes in soil acidity or alkalinity. This stability is vital for any technology intended for real-world agricultural use, where conditions are rarely as controlled as they are in a laboratory.

Ultimately, this research provides a green and efficient pathway for solving one of the most persistent problems in modern agriculture. By combining the natural filtration properties of biochar with the targeted power of biological enzymes, the researchers have created a sustainable tool that can help farmers maintain healthy, productive fields for longer periods. While further long-term field studies are needed to fully evaluate the impact on soil microbial life, these initial findings represent a major step forward in agricultural remediation. The successful detoxification of pepper soil highlights the potential for this technology to promote sustainable crop production and secure our global food supply.

Source: Zhang, X., Lv, S., Yuan, T., Fu, K., Yang, P., Yao, Y., Liang, J., Gao, T., & Wang, F. (2026). Efficient allelochemical removal from continuous capsicum cultivation using horseradish peroxidase-loaded biochar. Biochar, 8(2).