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The Impact of HTL-Derived Biochar on Seedling Growth of Lettuce ( Lactuca s ativa )

¹ Department of Environmental and Civil Engineering, Mercer University, Macon, GA, USA
² Department of Environmental and Civil Engineering, Mercer University, Macon, GA, USA
³ Department of Mechanical Engineering, Mercer University, Macon, GA, USA
⁴ Department of Environmental and Civil Engineering, Mercer University, Macon, GA, USA
⁵ Department of Cooperative Extension, University of Maine, Orono, ME, USA

Agricultural Sciences·Volume 16 (2025)·Pages 1452–1462·Published 3 December 2025·DOI10.4236/as.2025.1612084

Abstract

Biochar, also known as hydrochar, is a solid residue resulting from organic matter being combusted in low or no-oxygen environments, such as during the process of pyrolysis, gasification, or hydrothermal liquefaction (HTL). Biochar resulting from the HTL conversion process is considered a waste product and often an environmental liability, though there have been some studies on the potential uses for HTL biochar, such as a potential soil amendment. For this study, the biochar generated via the HTL conversion of various food waste feedstocks ( i . e ., food waste produced from beer-making and coffee brewing) was utilized to evaluate the effects of biochar as a soil amendment on plant growth. A series of seedling plant growth studies utilizing controlled environmental conditions were conducted with the addition of 0.0%, 2.5%, 5.0%, and 7.5% (m/m) biochar added to the soil medium. After three weeks, seedling plants were measured to have an overall wet weight of 0.65 to 0.73 g/seedling, a dry weight of 0.05 to 0.06 g/seedling, and a total leaf area of 10.6 to 12.4 cm/seedling. The seedlings grown in the soil mixture without the addition of biochar ( i . e ., the control) yielded the highest total leaf area, and the seedlings grown in the soil mixture with the addition of 2.5% (m/m) biochar yielded the second highest total leaf area. Overall, no statistically significant impact on seedling structure in soil containing between 2.5% and 7.5% (m/m) biochar was found as compared to seedling growth in soil without the addition of biochar. There is some evidence for increased biochar content reducing leaf area; however, further studies are required. Additionally, it is possible that biochar had some impact on seedling growth or structure, but the nutrients contained in the watering solution used in this study may have obscured its effects. Nevertheless, the results of this study are instrumental in evaluating a potential use of an HTL by-product ( i . e ., biochar) that is often considered an environmental liability.

KeywordsHydrothermal LiquefactionBiocharSeedling StudyLactuca s ativa

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The Impact of HTL-Derived Biochar on Seedling Growth of Lettuce ( Lactuca s ativa )

Abstract

References (41)