Depletion of soil organic carbon and nutrients poses significant challenges for agricultural production in tropical regions, threatening livelihoods and food security. To address this, Betelhem Mekonnen and a team of 21 other authors, in their study published in Biofuels, Bioproducts and Biorefining in May 2025, investigated the effectiveness of biochar-based fertilizers (BBF) in improving wheat yields and soil properties in acidic tropical soils. Their findings highlight BBF as a promising, sustainable alternative to conventional fertilizers, particularly in regions facing soil acidity and fertility decline.

The study, conducted across various sites in the Oromia and Sidama regions of Ethiopia, focused on two main BBF formulations: biochar-digestate and biochar-vermicompost. 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, a carbon-rich material produced from 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 of agricultural residues like coffee husk, is known to improve 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, porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More, and water-holding capacity. When enriched with nutrient-rich materials such as digestate (a byproduct of anaerobic digestion rich in nitrogen, phosphorus, and potassium) or vermicompost (derived from organic matter decomposition by earthworms), biochar’s fertilizing efficacy is significantly enhanced. The coffee husk biochar used in the experiments had a pH above 10, indicating its potential to raise low soil pH.

The results demonstrated that combining biochar with organic and/or inorganic fertilizers substantially increased above-ground 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 and dry grain yield in acidic soils. The most significant improvements were observed with application rates of 20 tonnes per hectare, which outperformed inorganic fertilizers by boosting grain yields by up to 94% and biomass by 58% in highly acidic highland soils. For example, at Ilala, a highland site with lower soil pH (3.93-4.34), BBF treatments at 20 tonnes per hectare led to grain yields of 2.77-4.61 tonnes per hectare. Even at a lower application rate of 5 tonnes per hectare, BBF resulted in a 62% increase in grain yield and a 33% increase in biomass yield compared to inorganic fertilizer and digestate alone.

Beyond yield increases, soil analyses revealed that BBF effectively improved soil properties. It increased soil pH, nutrient availability (such as phosphorus and nitrogen), and cation exchange capacity (CEC), which is crucial for nutrient retention. For instance, at Ilala, BBF treatments, particularly those with a higher proportion of biochar applied at 20 tonnes per hectare, increased soil pH from 4.18 (control) to 5.13. This liming effect of biochar helps mitigate soil acidity, a widespread problem in tropical regions where high rainfall exacerbates nutrient leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More.

The study noted that the effectiveness of BBF varied with initial soil conditions, showing a more pronounced impact in highly acidic and nutrient-poor soils compared to less acidic or more fertile ones. This highlights BBF’s specific role in addressing critical soil deficiencies. While the impact on soil organic carbon (SOC) content was inconsistent and not always statistically significant after a single application, the long-term stability of biochar in soil suggests its potential for sustained carbon sequestration and structural improvement over multiple cropping seasons.

The findings advocate for the adoption of BBF into integrated soil fertility management practices, as it can reduce reliance on imported inorganic fertilizers, promote a circular bioeconomy by utilizing agricultural waste, and contribute to carbon sequestration. For smallholder farmers, who often face financial burdens from costly imported fertilizers, locally produced BBF represents a viable and sustainable option for enhancing agricultural productivity and soil health.

Source: Mekonnen, B., Wilske, B., Addisu, B., Nigussie, A., Siegfried, K., Gizachew, S., Yimer, T., Mohammed, B., Ahmed, M., Abera, T., Nebiyu, A., Worku, R., Regassa, A., Firomsa, T., Husien, A., Worku, G., Lema, A., Tilahun, A., Assefa, K., Dume, B., Eshete, G., & Pollex, A. (2025). Biochar-based fertilizers increase crop yields in acidic tropical soils. Biofuels, Bioproducts and Biorefining.