The project was composed in two parts. The first, laboratory testing of biochar amended highway soils on stormwater infiltration, retention, and soil structure at different degrees of compaction, with or without turfgrass. The second part of the study was conducted at test plots along DE 301 to determine if wood-derived biochars alters aggregation, root characteristics, and hydrologic properties when amended into bioretention soil medias (BSM).
The lab study found that biochar amendments increased total porosity by 10% when amended with 2% biochar by weight, and by 24.4% when amended with 4% biochar by weight. Biochar amendments also increased porosity of compacted soil treatments by 11.6% and 35.5% respectively when amended with 2% and 4% biochar by weight. Additon of biochar also increased organic matter by 29-70% when amended with 2% biochar, and by 100-220% when amended with 4% biochar. In the field study, two representative bioretention soil medias (BSM) were amended with wood biochar, planted with switchgrass and monitored for 30 weeks. Biochar amendments increased stormwater retention and infiltration and hydraulic conductivity with the effects increasing over time. Improvements in hydraulic performance was correlated with an increase in media aggregation in high-sand BSM.
