Cucumber and tomato seedling growth effects by biochar supplemental rates

Studies on the effects of biochar on seedling emergence are limited despite the popularity of biochar. The objective of this study was to evaluate the use of biochar as a soilless media supplement for the emergence of cucumber 'Diva' and tomato 'Early Girl F1' seedlings. Eastern red cedar (ERC) biomass was produced at 300–350 °C, 400−450 °C, and 500−550 °C, and was incorporated with soilless media at rates (15%, 30%, 45%, and 60% v/v) plus a soilless media only. ERC bark was also applied at the same rates to the soilless media. Emergence rate and growth characteristics along with nutrient properties of the plant and media were recorded. For tomatoes, a lower rate of biochar (15%) produced at all three temperatures reduced the days for emergence by 12%−16% compared to 100% soilless media. Among biochar treatments, seeds emerged faster with 15% which increased by 7.1% to 16% compared to 30% and greater. Soilless media had the greatest tomato seedling height, width, shoot dry weight, and number of leaves but were similar to lower rates (up to 30%) of biochar produced at different temperatures, which outperforms the 45% and 60% rates. Whereas, for cucumber, the greatest days (10 d) required for emergence was with 60% ERC bark. Among biochar treatments, 15% biochar produced at 300−350 °C required the least days (reduced emergence days by 3 d for emergence while 45% biochar produced at the same temperature required greater days to emerge. The greatest height was with 30% biochar produced at 500−550 °C, while the greatest width was with 30% biochar produced at 300−350 °C. The 60% biochar produced at 300−350 °C had the greatest chlorophyll content. The greatest number of leaves and shoot dry weight were with 100% soilless media. In general, 100% soilless media outperforms the higher biochar mixes, however, the lower rates of biochar showed significantly similar effects as the 100% soilless media. This study found biochar produced at 45% or less at any temperature studied can be used for cucumber seedlings' emergence, while no more than 15% biochar produced at all three temperatures should be used for tomato seedling emergence.