Tomato production plays a central role in agricultural security and local economies across Eastern Africa, yet smallholder farmers frequently experience suboptimal harvest yields due to soil nutrient depletion and the prohibitive expense of imported synthetic fertilizers. At the same time, the inadequate management and disposal of rural anaerobic cow dung bioslurry and urban charcoal waste create persistent ecological waste challenges. To solve both issues simultaneously, a research team published a study in PLOS One led by Girmaw Mulugeta, Ermias Alayu, and Yitayal Addis Alemayehu, examining how combining these organic waste streams into a unified 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 influences crop productivity and soil chemistry.

The experimental trial evaluated five distinct formulations of co-composted 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 and bioslurry against unamended soil, raw bioslurry, and standard synthetic chemical fertilizer treatments over a full growth cycle in a controlled greenhouse environment. Quantitative assessments revealed that the co-composted formulations maintained elevated concentrations of essential soluble plant nutrients, with organic carbon levels ranging from 26.8 percent to 65.6 percent, ammonium levels reaching between 2.5 and 4.6 milligrams per liter, and orthophosphate concentrations ranging from 0.74 to 3.1 milligrams per liter. The physical properties of the incorporated charcoal provided an alkaline buffer with a 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 of 8.2 and a total pore volume of 8.8 milliliters, generating structural conditions favorable for long-term nutrient retention and microbial activity.

Plant biometric evaluations demonstrated that organic co-compost formulations equaled or surpassed synthetic chemical inputs across key growth indicators. Pots treated with bioslurry combined with a ten percent increased charcoal ratio achieved an average tomato fruit yield of 2.87 kilograms per pot, outperforming the 2.73 kilograms per pot recorded for synthetic commercial fertilizer treatments and dramatically exceeding the 0.71 kilograms per pot produced by unamended control soils. Crop structural development followed a similar trajectory, as stem diameters reached 2.40 centimeters and plant heights reached 17.66 centimeters under charcoal-enriched treatments, compared to 1.83 centimeters and 7.00 centimeters in control conditions.

Analysis of post-harvest soil samples confirmed substantial residual improvements in overall land quality and nutrient availability. Total soil nitrogen increased to 24.10 percent under the highest co-compost application rate, while total phosphorus increased from a baseline of 0.94 milligrams per liter up to 39.9 milligrams per liter. Furthermore, essential exchangeable cations showed marked increases, with potassium reaching 14.70 milligrams per liter and calcium reaching 15.90 milligrams per liter. These quantitative increases confirm that integrating charcoal into bioslurry composting mitigates 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, neutralizes soil acidity, and provides a sustainable alternative to commercial synthetic inputs.

Source: Mulugeta, G., Alayu, E., & Alemayehu, Y. A. (2026). Synergetic effect of bioslurry and charcoal co-composted fertilizers on soil properties and tomato (Solanum lycopersicum) productivity. PLOS One, 21(7), e0353951.