Modern agriculture faces significant challenges from trace metal contamination in soil, primarily due to industrial effluents and wastewater irrigation, which degrade food quality and reduce crop productivity. To tackle this pressing issue, a recent study by Kaushik Gautam, Rajeev Pratap Singh, and Anita Singh, published in Environmental Sustainability, investigated the effectiveness of simple and potassium permanganate (KMnO4​)-modified rice husk 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 in improving soil attributes, regulating metal uptake, and enhancing the growth of beetroot plants.

The researchers applied simple and modified rice husk biochar at different doses: 15, 20, and 30 tonnes per hectare (t/ha) to wastewater-irrigated soil. The modification with KMnO4​ (0.01 M) was intended to enhance the biochar’s surface area and active functional groups, thereby improving its adsorption efficiency. The study found that modified biochar significantly improved soil functional properties and mineral content compared to control soil.

A key finding was the dose-dependent reduction in heavy metal concentrations in both the soil and the beetroot plants, with modified biochar demonstrating greater efficiency than simple biochar. At the highest dose of 30 t/ha of modified biochar, the concentrations of cadmium (Cd), nickel (Ni), zinc (Zn), chromium (Cr), cobalt (Co), and lead (Pb) in beetroot plants decreased by a remarkable 81%, 80%, 56%, 80%, 61%, and 72%, respectively, compared to untreated control plants. The roots consistently showed higher heavy metal levels than the shoots, but the reduction was still significant. For instance, in roots, modified biochar at 30 t/ha reduced Cd by 83%, Ni by 87%, Zn by 51%, Cr by 84%, Co by 68%, and Pb by 78%.

Beyond metal reduction, biochar application positively influenced the soil’s physicochemical properties, including 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, electrical conductivity (EC), soil organic carbon (SOC), total nitrogen (TN), and available phosphorus (AP). For example, at 30 t/ha, modified biochar increased SOC by 61%, TN by 320%, and AP by 39% compared to control soil. These improvements are crucial for overall soil health and nutrient availability. The study also observed significant increases in soil microbial biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More carbon (MBC) and microbial biomass phosphorus (MBP), by 41% and 45% respectively, with modified biochar at 30 t/ha, indicating enhanced microbial activity vital for nutrient cycling.

The application of biochar also boosted the activity of soil enzymes such as beta-glucosidase (BGL), acid phosphatase (ACP), alkaline phosphatase (ALKP), and dehydrogenase (DHA). Modified biochar at 30 t/ha led to a 95% increase in BGL activity, a 218% increase in ACP activity, and a 125% increase in ALKP activity. These enzymes are essential for carbon and phosphorus mineralization and are sensitive indicators of soil health.

In terms of plant health, biochar application reduced oxidative stress markers like hydrogen peroxide ( H2​O2​), malondialdehyde (MDA), and superoxide reductase (SOR) in both beetroot shoots and roots. Modified biochar at 30 t/ha reduced H2​O2​ in shoots by 63% and in roots by 49%. MDA content was reduced by 73% in shoots and 76% in roots at the same dose. Concurrently, the activities of antioxidative enzymes such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) increased significantly. Modified biochar at 30 t/ha led to a 509% increase in CAT activity in shoots and a 371% increase in roots, demonstrating a stronger defense mechanism against heavy metal stress.

Most importantly, the study revealed that the maximum increment in plant yield was observed at a lower dose of 15 t/ha of modified biochar. At this dose, fresh weight increased by 37%, shoot length by 25%, and root length by 108% compared to control plants. Chlorophyll a and b, and carotenoid contents also saw significant increases, with modified biochar at 15 t/ha increasing chlorophyll a by 136% and chlorophyll b by 188%.

This research underscores the potential of KMnO4​-modified rice husk biochar as a sustainable soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More for mitigating heavy metal stress, improving soil health, and enhancing crop productivity in contaminated environments. The findings align with Sustainable Development Goals by promoting eco-friendly solutions for agriculture and soil restoration. Future research should focus on optimizing application rates and assessing long-term effects in various soil types and field conditions.

Source: Gautam, K., Singh, R. P., & Singh, A. (2025). Physicochemical and functional characterization of wastewater-irrigated soil and beetroot plants in response to modified rice husk biochar amendment. Environmental Sustainability