ASHS 2025 Conference

Biochar, a carbon-rich material produced from biomass pyrolysis, has potential to absorb and provide mineral nutrients for plant growth. Anaerobic digestion is a process where microbes decompose organic material without oxygen in sealed vessels to produce digestate and biogas. In this study, biochar was utilized to sequester mineral nutrients during anaerobic digestion of vegetable waste and used to deliver nutrients to a growing leafy green vegetable. Fresh vegetable biomass was used as a feedstock in a novel 80 L cartridge anaerobic digester in Spring 2024. Biochar was placed in the digester liquid effluent for a minimum of 30 days to absorb nutrients liberated by the digestion process. Biochar was analyzed for nitrogen, phosphorus, and potassium content to determine plant culture treatment levels. A plant culture greenhouse experiment (lat. 40.51ºN; Normal, IL) was conducted in Fall 2024. Seeds of lettuce (Lactuca sativa ‘Newham’) were grown to transplant size. One week after seedling emergence, a soluble 20N-4.4P-16.6K fertilizer was applied to seedlings every seven days at a rate of 100 mg/L N. Approximately three weeks after emergence, individual plants were transferred to 3.8 L plastic pots filled with soilless media. Fertility treatments were maintained at 70 mg/L N using the following ratios of commercial 20N-4.4P-16.6K Fertilizer:Biochar;100%:0%, 90%:10%, 80%:20%, 70%:30%, and 60%:40% by weight, respectively, as a media-incorporated, preplant application. Pots were arranged in a completely randomized block design. During plant growth, media Electrical Conductivity (EC) and leaf Soil Plant Analysis Development (SPAD) were measured every five days. Media EC decreased (P≤0.001) and leaf SPAD increased (P≤0.001) across all treatments during growth. Lettuce was harvested at 50 days post-seeding when it reached marketable size. At harvest, shoot and root fresh mass were measured, and fresh tissue was dried at 60ºC for dry mass determination. For lettuce, total biomass, shoot FM, root FM, shoot DM, and root DM at harvest all decreased, and then increased quadratically (P≤0.001) as Fertilizer:Biochar ratios changed from 100%:0% to 70%:30%. The highest lettuce per plant total biomass was 176.92 g per plant under 100% commercial fertilizer. Harvest EC increased linearly (P≤0.001) and SPAD decreased, then increasing quadratically (P≤0.001) as Fertilizer:Biochar ratios changed from 100%:0% to 60%:40%. Observed Fertilizer:Biochar response patterns indicate a delayed nutrient release from biochar over time. Additional research on the timing of nutrient release from biochar and possible uses as a commercial fertilizer for vegetable crop production continues to be warranted.