A new study reveals that applying Tea Waste Biochar (TWB) to soil dramatically enhances onion growth and overall yield. The research, published in Discover Plants by Riaz et al., evaluated the impacts of TWB, farmyard manure (FYM), and NPK chemical fertilizers on the soil’s physicochemical properties and the resulting onion harvest. The authors found that TWB significantly outperformed the other treatments, offering a promising, sustainable alternative for cultivation.

Tea Waste Biochar, produced through a process called slow 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, proved to be an effective organic amendment. The analysis showed that TWB had a higher electrical conductivity compared to FYM and NPK fertilizers. This difference indicates a greater concentration of dissolved ions in the soil solution after the biochar application. Furthermore, the TWB treatment significantly increased the soil’s water-holding capacity than dry soil and its organic matter content. The structural analysis of the TWB, which was derived from used tea leaves, revealed irregularly shaped, highly porous particles with micropores. This inherent 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 large surface area are believed to be the reason behind the superior soil moisture retention and reduced soil bulk density observed in the biochar-treated plots.

The study also focused on the available nutrients in the soil after treatment. TWB application led to the highest recorded nitrate nitrogen and available potassium .The higher nitrate is likely due to the biochar’s ability to improve the retention of plant nutrients, thus minimizing nitrogen losses through 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. This is a critical factor for crop health, as adequate nutrient supply is vital for the synthesis of key growth-regulating compounds in plants. While TWB did not significantly affect the Olsen-P levels, both FYM and NPK treatments bolstered this phosphorus content.

Perhaps the most compelling results were those related to the final onion crop. Plots treated with Tea Waste Biochar recorded the highest values for all measured growth parameters. TWB-treated plots yielded appreciable bulb weight and leaf length in comparison to the control (CK) plots. Ultimately, the maximum total onion yield of 268.3kg/ha^-1 was recorded in the TWB treatment, which is significantly higher than that recorded in the control plots. This dramatic increase in yield is attributed to the combination of enhanced soil physical properties, improved aeration, and greater nutrient availability facilitated by the TWB. This robust performance demonstrates that TWB effectively enhances soil fertility and promotes plant growth, providing an economically sound option for farmers since the production cost of tea waste biochar is slightly lower than biochar from some straw 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.

Beyond the agricultural benefits, the use of tea waste biochar aligns with sustainable waste management goals. By converting a common by-product into a valuable 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, it addresses the issue of organic matter deficiency in soils while reducing reliance on synthetic fertilizers. The final analysis indicated that the influence of soil properties on onion yield is primarily mediated through enhanced plant growth and nutrient uptake, underscoring the importance of healthy soil for increased crop production. The correlation analysis further supported these findings, showing that biochar exhibited strong positive correlations with soil organic matter, water-holding capacity, and overall onion yield.

Source: Riaz, M., Khan, S., Shah, T., Tariq, M., & Khan, M. I. (2025). Enhancing Allium cepa L. cultivation through sustainable soil management with biochar, manure and NPK fertilizers. Discover Plants, 2(1), 353.