Farmers worldwide face a stubborn problem: soil that is too salty or alkaline. These “saline-sodic” soils make it difficult for crops to absorb water and nutrients, leading to poor growth. One promising tool for fixing this is biochar made from heating 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 like rice or wheat straw in a low-oxygen environment. But can we make biochar even better for this specific job? A new study by I. Shehzad and colleagues, published in the SABRAO Journal of Breeding and Genetics, explores this exact question. They didn’t just use regular biochar; they “modified” it with strong acids to see if they could improve its properties for soil remediation.

One of biochar’s benefits is its ability to change soil pH. The untreated biochars in this study were neutral-to-alkaline: 7.6 for rice straw and 7.1 for wheat straw. This is fine for some soils, but to fix alkaline soils, you want an acidic amendment to help neutralize them. This is where the acid treatment shined. Both hydrochloric acid (HCl) and sulfuric acid ) successfully made the biochar more acidic. However, sulfuric acid was the clear winner. It dropped the wheat straw biochar’s pH all the way down to 5.4 (acidic), while HCl only got it to 6.0 (slightly acidic). The authors explain this is likely because sulfuric acid is “diprotic,” meaning it releases twice as many acidifying protons (H+ ions) as HCl, giving it more neutralizing power.

The second major issue in problem soils is high electrical conductivity (EC), which is a direct measure of dissolved salts. High EC is toxic to most plants. The untreated rice straw biochar actually had a fairly high EC of 1.51 dSm-1, meaning it could add to a salinity problem. The wheat straw biochar was better, starting at 0.75 dSm-1. The acid treatments helped “clean” the biochar by washing out these soluble ions. Once again, sulfuric acid was the star performer. It slashed the EC of the wheat straw biochar by an impressive 63%, taking it from 0.75 down to just 0.28 dSm-1. This makes the modified biochar a much safer and more effective amendment for soils already struggling with high salt content.

However, this aggressive acid-washing comes with a trade-off: nutrients. Biochar naturally contains important plant nutrients like nitrogen (N), phosphorus (P), and potassium (K). The study found that the acid treatments, especially sulfuric acid, also washed away some of these beneficial compounds. For example, the untreated rice straw biochar had the highest potassium (K) content at 3.85%. After the treatment, this dropped to 2.9%. Similarly, the highest phosphorus (P) content, found in untreated wheat straw biochar (2.65%), fell to 2.4% after the same treatment. This doesn’t make the biochar useless, but it suggests farmers might need to use it along with other fertilizers to make up for this nutrient loss.

So, what’s the final verdict? This study clearly shows that not all biochar is created equal. By modifying the biochar with sulfuric acid, the researchers created a “designer” 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. They successfully lowered its pH and dramatically reduced its salt content, turning it into a powerful, specialized tool for reclaiming difficult farm soils. The key is to be aware of the trade-offs. The resulting product is lower in some key nutrients, but its ability to fix the soil’s fundamental pH and salt problems could be far more valuable. This research opens the door for creating customized biochars designed to solve specific agricultural challenges.

Source: Shehzad, I., Sarwar, G., Mahmood, A., Manzoor, M. Z., Luqman, M., Usman, M., Peerzado, M. B., Ashraf, M., & Gul, S. (2025). Characterization of different types of biochars and their modified forms. SABRAO Journal of Breeding and Genetics, 57(5), 2166-2176.