Amendment of a hardwood biochar with compost tea: effects on plant growth, insect damage and the functional diversity of soil microbial communities

Biochar is an organic soil amendment that has been shown to improve plant growth and increase resistance to plant diseases and insect damage in certain soils. Organic growers have been known to use compost teas to amend biochar, claiming that this practice adds nutrients and beneficial microorganisms that can improve plant growth and resistance to pathogens and insect pests. However, few data exist to support this hypothesis. This study investigated the effects of a hardwood biochar amended with different types of compost teas and microbial enrichments (prepared from vermicompost) on eggplant (Solanum melongena var. Rosa Bianca) growth, flea beetle (Epitrix fuscula) damage, and soil microbial activity and functional diversity in two temperate soils. No positive short-term effects were observed on eggplant growth or flea beetle damage when biochar amended with compost teas prepared from horse manure, mushroom compost or vermicompost were added to a temperate agricultural soil. However, a second experiment suggested that biochar amended with microbial enrichments from vermicompost tea may improve eggplant growth if matched with the physical and chemical properties of a given soils. Results from Community Level Physiological Profiling (CLPP) revealed that biochar amended with compost teas altered soil microbial activity and functional diversity differently to that of biochar alone, and that these changes corresponded with plant growth and insect damage.