Impact of the application of biochar previously used in domestic wastewater treatment on the growth of lettuce ( Lactuca sativa) Edna Buhnyuy Visiy* Pan African University, Life and Earth Sciences Institute (Including Health and Agriculture), Ibadan, Nigeria Boris Merlain Kanouo Djousse Department of Agricultural Engineering, University of Dschang, Cameroon Abimbola Sangodoyin Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria Adeniyi Sulaiman Gbadegesin Department of Geography, University of Ibadan, Ibadan, Nigeria Theophile Fonkou Department of Plant Biology, University of Dschang, Dschang, Cameroon *Corresponding author. Email: visiyedna@gmail.com Article Info https://doi.org/10.31018/ jans.v14i3.3731 Received: July 5, 2022 Revised: August 14, 2022 Accepted: August 20, 2022 This work is licensed under Attribution-Non Commercial 4.0 International (CC BY-NC 4.0). © : Author (s). Publishing rights @ ANSF. ISSN : 0974-9411 (Print), 2231-5209 (Online) journals.ansfoundation.org Research Article INTRODUCTION Soil nutrient depletion is an important concern, directly linked to food insecurity due to unsustainable land use practices. Many tropical soils are highly degraded and depend on recycling nutrients from soil organic matter and fertilizers to maintain fertility (Djousse et al., 2019). Inorganic fertilizers have played a significant role in increasing agricultural productivity; their benefits cannot be overlooked. However, excessive fertiliser application to agricultural land may result in soil deterioration (Agegnehu et al., 2017) and may have detrimental ef- fects on human health. Moreover, fertilizer costs have increased since the onset of the war in Ukraine, dis- rupting the flow of supplies from Russia, the world’s largest commodity exporter. The surging cost of chemi- cal fertilizers has contributed to higher global prices for food and hence a need for more sustainable farming solutions that depend less on applying fertilizers. In some cases, farmers resort to compost and manures to enhance soil fertility. But, organic matter is usually min- eralized very rapidly under tropical conditions leaving only a small portion of it stabilized in the soil in the long term, with most released back to the atmosphere as Abstract Biochar has gained attention in agricultural studies due to its ability to ameliorate soil conditions. However, due to its low nutri- ent content, positive effects on plant growth are generally only observed if combined with mineral fertilizers or manures. The study aimed to test the hypothesis that biochar used to treat domestic wastewater can become enriched with nutrients and sub- sequently serve as a better soil amendment. The impact of the application of biochar used as substrate in a filter for domestic wastewater treatment (TB) on the growth of lettuce ( Lactuca sativa var. crispa) plant was evaluated. Its effect on plant growth was compared to pure biochar (BC) using bare soil as a control. The biochars were applied with and without fertilizer using 3 biochar application rates (10, 20 and 30 t/ha). Results showed that biochar does not become enriched after wastewater purifica- tion in the short run. Instead, there was a reduction in the mineral composition, available phosphorus and pH in TB compared to BC. Only the BC treatments were significantly different (p=0.001) from the control. However, higher biomass production at 30 t/ ha was observed in BC (+322%) and TB (+142%), compared with the unfertilized control. There were no significant differences in biomass production between the biochar and control treatments for application rates below 30 t/ha. Fertilization significantly (p=0.024) improved biomass production with the BC30+F treatments demonstrating the highest performance (+315%) com- pared to the fertilized control. Keywords: Biochar, Lactuca sativa, Plant growth, Treated biochar, Wastewater treatment How to Cite Visiy, E. B. et al. (2022). Impact of the application of biochar previously used in domestic wastewater treatment on the growth of lettuce (Lactuca sativa). Journal of Applied and Natural Science, 14(3), 963 - 970. https://doi.org/10.31018/jans.v14i3.3731