Tomato seed germination and transplant growth in a commercial potting substrate amended with nutrient-preconditioned Eastern red cedar (Juniperus virginiana L.) wood biochar

Most soilless substrates currently used by the greenhouse and nursery industries for transplants use lightweight materials including peat moss, vermiculite and perlite. Because these materials lack sufficient nutrients, slow-release synthetic fertilizers are added which have sustained release patterns that are sufficient to maintain optimal plant growth until the plants are placed in gardens. Biochar has physical and chemical properties (e.g., light weight, high water and nutrient absorption capacity) which allow it to be both a significant component of soilless potting substrates as well as acting as a slow-release fertilizer when preconditioned with nutrients, either from inorganic or organic sources. Biochar produced in a kiln from Eastern red cedar (ERC, Juniperus virginiana L.) wood was found to have high porosity, potentially allowing it to absorb large amounts of nutrients and subsequently re-release the nutrients over an extended period of time, allowing it to be utilized in slow-release fertilizers for transplant substrates. Experimental slow-release fertilizers were produced from ERC biochar that were infused under a vacuum with both a commercial synthetic hydroponic fertilizer and an organic fishemulsion liquid fertilizer. Seed germination, seedling growth and transplant growth parameters of tomato (Solanum lycopersicum L. 'Red Robin') plants grown in a commercial peat moss-based potting substrate supplemented with 5, 10 and 20 % (v%/v%) of both organic and inorganic fertilizer-infused ERC biochar were examined, utilizing commercially-available slow-release chemical fertilizers as the control. When utilized as a starter substrate, seed germination was significantly inhibited in both 20 % ERC biochar substrates. When used as a transplant substrate, fresh weights of tomato plants grown with 10 and 20 % inorganic biochar fertilizer, and dry weights of these treatments as well as the 20 % organic biochar fertilizer were similar to the control. Final plant heights with both 20 % inorganic and organic ERC biochar fertilizers were equal to the control, with SPAD values (indicating chlorophyll content and nitrogen status of the plants) was highest in plants grown in 20 % inorganic biochar. These results indicate that ERC biochar has potential as a slow-release fertilizer for both starter and transplant substrates when preconditioned with both inorganic and organic fertilizers, although the higher levels of preconditioned ERC biochar should not be used in starter substrates.