A new study published in The International Journal of Life Cycle Assessment by Stijn van de Lande, Pia Berger, and Gijsbert Korevaar highlights a crucial, often overlooked aspect of biochar’s environmental impact: its effects on soil. While most life cycle assessment (LCA) studies focus on 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 production, this research establishes a comprehensive approach to model its soil effects, concluding that they can have a far greater influence on environmental outcomes than previously recognized. The authors conducted a case study in Aguascalientes, Mexico, to demonstrate how these soil effects can be quantified and how their influence on key impact categories, such as climate change and water depletion, can be understood.

Biochar is known for its ability to sequester carbon. However, its application to agricultural fields triggers a cascade of “soil effects” like nutrient retention, enhanced microbial activity, and improved water buffering capacity. The authors found that these soil effects are the single largest contributor to biochar’s overall environmental impact across nearly all categories. In fact, biochar production and preparation impacts are often overshadowed by the consequences of its application to soil. This finding underscores why LCA studies that omit or incompletely model soil effects may present a skewed picture of biochar’s true environmental footprint.

In the Aguascalientes case study, the model assumed a dry, degraded, and acidic soil, conditions where biochar is expected to have a relatively high impact. The results showed that biochar application led to a net environmental benefit in most impact categories, a result heavily influenced by which soil effect data was chosen for the model. The most significant environmental benefits came from two key soil effects: crop yield increase and water retention. The increase in crop yield displaced the need for agricultural production elsewhere, thereby reducing environmental impacts like acidification by almost 90% and photochemical oxidation by a substantial amount. Water depletion was primarily reduced by biochar’s water retention effect (80%), with the remaining 20% coming from the crop yield increase offsetting the need for irrigation on other land.

While the benefits were substantial, the study also identified some negative environmental impacts. Biochar contains toxic compounds, such as chromium (46%), mercury (29%), arsenic (20%), and zinc (7%), which can increase terrestrial and aquatic ecotoxicity. This highlights the importance of tailoring biochar production to minimize risks. The authors suggest that avoiding feedstocks high in chlorine, such as food waste, could reduce dioxin levels, while adjusting 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 temperatures (outside the 350-550°C range) can lower concentrations of polycyclic aromatic hydrocarbons (PAHs).

The study acknowledges several limitations to accurately modeling biochar’s effects, most of which are data-related rather than conceptual. Biochar’s effects are non-linear, meaning doubling the application rate does not double the environmental benefit, a fact that challenges conventional LCA models. The long-term durability of biochar’s effects is another major uncertainty, as some effects are transient while others, like those found in Amazonian “Terra Preta” soils, may last for thousands of years. To address these challenges, the authors propose a biochar-soil classification system to standardize data and recommend the use of biogeochemical models to fill in the gaps left by limited long-term field data.

Source: van de Lande, S., Berger, P., & Korevaar, G. (2025). Including biochar’s soil effects in lifecycle assessment: application to a practice-oriented case study in Aguascalientes, Mexico. The International Journal of Life Cycle Assessment.