In a study published in the Journal of the Ghana Institution of Engineering, authors Ibo Zimmermann, Inekela Eita, Simeon I. Ambuga, and Veikko Shalimba explored how converting invasive bush 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 into biochar could benefit agriculture. Their research focused on Namibia, where bush encroachment poses a significant threat to rangelands by reducing available grazing area and stripping soil nutrients. By thinning these bushes and processing them into biochar, farmers have an opportunity to return vital carbon to the earth. The researchers utilized a radish bioassay to quickly determine if mixing two percent biochar by volume into silty loam soil would improve plant performance or alter soil characteristics within a five-week growing period.

The most striking result of the experiment was the dominant role of fertilizers compared to the biochar treatment. While the biochar did not produce a significant short-term change in growth, the application of a fertilizer mix—including bone char, worm tea, wood vinegar, and chicken manure pellets—led to a highly significant boost in yield. Plants receiving fertilizer were forty-two percent heavier on average than those that were not fertilized. The physical dimensions of the radishes also improved, with fertilized tubers being thirteen percent wider and their leaves growing twenty-three percent longer. Furthermore, there was a slight improvement in the quality of the radish sap, with fertilized plants showing five percent higher sugar content, although this result was only marginally significant.

Regarding soil health, the research provided promising evidence that biochar acts as a stabilizing agent for nutrients. In the growing bags that received both biochar and fertilizer, the calcium content was twenty-six percent higher than in bags that received only fertilizer. This finding suggests that the biochar helped bind the calcium provided by the organic amendments, preventing it from 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 out during watering. In contrast, pots without biochar lost more calcium over the five-week period. This indicates that while biochar may not always drive immediate visible growth in the first month, it plays a vital role in the circular bioeconomy by preventing nutrient waste and holding onto the “wealth” provided by supplemental fertilizers.

Interestingly, the study found no significant immediate effect of biochar or fertilizer on the soil’s water holding capacityWater holding capacity is the amount of water that soil can retain. Biochar can significantly increase the water holding capacity of soil, improving its ability to withstand drought conditions and support plant growth.   More. The researchers noted that the silty loam soil used was already quite compacted in the pots, which may have masked any potential improvements in hydration. They also observed that the failure of biochar to significantly increase water retention in this short timeframe might be due to the specific method of mixing it evenly throughout the soil. Other long-term studies have shown that it can take several years for biochar to develop a stronger chemical charge and be fully conditioned by soil microbes to significantly boost moisture levels.

Ultimately, the most useful takeaway for practitioners is the confirmation that applying biochar at a rate of two percent by volume is safe and causes no short-term harm to crops. This application rate is roughly equivalent to fourteen to thirty tons per hectare depending on the depth of the soil. For farmers in regions with alkaline soils, the lack of negative effects is a green light to begin incorporating this waste-to-wealth product. While the immediate growth benefits are largely driven by organic fertilizers, the long-term presence of biochar in the soil serves as an insurance policy for nutrient retention and structural stability. The radish bioassay proved to be an effective, low-cost tool for making these determinations quickly, providing a reliable guide for farmers before they commit to larger-scale field applications.

Source: Zimmermann, I., Eita, I., Ambuga, S. I., & Shalimba, V. (2025). Valorising encroacher bush biomass into biochar: Insights from a radish bioassay with and without fertiliser application. Journal of the Ghana Institution of Engineering, 25(3), 82-86. https//doi.org/10.56049/jghie.v25i3.362