In a study published in the journal Agriculture, lead author Anca Maria Zaharioiu and a team of researchers investigated how a specific byproduct from the paper industry could be repurposed to support sustainable farming. The team focused on black liquor, a highly alkaline and mineral-rich residue generated during the Kraft pulping process. By subjecting this liquid waste to controlled heating without oxygen, a process known as pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, they transformed it into biochar. This study demonstrates that instead of treating black liquor as a problematic industrial effluent, it can be valorized into an effective soil amendment that enhances the physical and chemical properties of agricultural land while supporting the early development of barley crops.

The experimental results revealed that the application of this biochar led to a dramatic improvement in soil fertility indicators. One of the most significant findings was the impact on cation exchange capacity, which serves as a measure of the soil’s ability to hold onto and supply essential nutrients to plants. The researchers observed that adding just three percent biochar to the soil increased this capacity from eleven to nineteen units, representing a seventy-three percent improvement over untreated soil. This enhancement is largely due to the porous nature of the biochar, which provides a vast surface area for nutrient attachment. Furthermore, the biochar acted as a stabilizer for soil organic matter, increasing its content by twenty-four percent. This change is vital for long-term soil health, as organic matter improves soil structure and water retention.

Beyond improving the soil itself, the biochar had a clear positive effect on the growth and physiological health of barley plants. During the thirty-day observation period, plants grown in the biochar-amended soil reached an average height of twenty-seven centimeters, which was an eight percent increase compared to those in the control group. More impressively, the leaf chlorophyll content, measured in SPAD units, rose by twenty percent. This indicates that the plants were better nourished and had a higher capacity for photosynthesis, likely due to the biochar’s ability to retain nitrogen and provide a steady supply of minerals like potassium and sulfur. While traditional chemical fertilizers provided a slightly higher immediate growth spurt, the biochar offered a more balanced and sustainable nutrient profile.

The chemical interaction between the biochar and the soil also highlighted its potential as a protective amendment. The biochar was found to be naturally alkaline, which helped raise the soil 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 from a neutral seven to a slightly alkaline seven-point-five. This property is particularly useful for neutralizing acidic soils, which often suffer from nutrient deficiencies and toxic levels of certain metals. In contrast, the study showed that conventional nitrogen fertilizers actually acidified the soil, dropping the pH to six-point-six. By acting as a pH regulator, the black liquor biochar ensures that phosphorus remains available to the roots and creates a more hospitable environment for beneficial soil microorganisms.

Ultimately, the study confirms that transforming industrial waste into biochar aligns perfectly with circular economy principles. By recycling the mineral-rich components of paper mill residues, farmers can improve soil quality and crop performance without the environmental drawbacks associated with the overuse of synthetic chemicals. The researchers concluded that this biochar serves as a functional material that bridges the gap between industrial waste management and sustainable agriculture. While further long-term field trials are necessary to confirm these effects over several growing seasons, the current findings provide a compelling case for using black liquor biochar as a high-value resource to bolster food security and environmental resilience.

Source: Zaharioiu, A. M., Tanislav, O. M., Constantinescu, M., Roman, A., Bucura, F., Niculescu, V.-C., Oancea, S., & Marin, F. (2026). Biochar Derived from Black Liquor as a Soil Amendment: Effects on Soil Quality, Growth Parameters, Chlorophyll and Mineral Content of Barley. Agriculture, 16(6), 659.