Effects of a Biochar-Amended Alkaline Soil on the Growth of Romaine Lettuce and Bermudagrass

Biochar from pine forest waste (PFW) was used in greenhouse pot experiments to evaluate plant growth using two levels (2% and 4% wt/wt) of biochar amendments applied to an alkaline, loamy sand soil. Biochar soil additions induced a large decrease in the soil bulk density (from 1.59 to 1.26 g cm⁻³) and large to moderate increases in gravimetric and volumetric soil-water contents, respectively, under pot and field moisture capacity conditions. The growth of romaine lettuce was initially adversely affected in the 4% biochar-amended soil. However, bermudagrass benefited from the biochar addition with increased biomass production and enhanced drought resistance. Both plant species showed statistically significant increases (compared with controls) in biomass yields at the 2% but not at the 4% biochar application rate. An incubation study indicated that soil microbial activity, as measured by evolved CO₂, was significantly suppressed (−31% compared with the control) in the presence of biochar over a period of 4 months. The data indicated that addition of PFW biochar induced a species-dependent plant response and produced an overall decrease in microbial mineralization of organic materials. Vegetables such as lettuce may benefit from a period of excess irrigation, to leach any potentially toxic biochar-introduced salts or organic compounds, before seeding. Conversely, warm season grasses may adapt quickly to a soil amended with PFW biochar with increased biomass production and drought resistance.