Effect of softwood biochars on earthworms in two contrasting soils in Southern Finland

Soil carbon sequestration is one of the most promising solutions to mitigate climate change. Biochar, a carbon rich solid obtained via pyrolysis and intended to be used as a soil amendment material, is currently the most efficient tool available for carbon sequestration. Further, some biochars can also improve soil properties and increase crop yield. Before the concept of using biochar as soil amendment can be implemented in a bigger scale, it is necessary to know how biochar affects soil fauna in long term. Earthworms present one of the largest animal biomass in soil. They feed on decomposed organic matter and also biochar and transfer it to pedosphere. Effect of biochars and fertilizers on earthworm abundance, biomass and community structure was studied in two field experiments, one on fertile Stagnosol and other on nutrient deficient Umbrisol. In both study sites, split-plot experiments with four replicates were arranged. The earthworms were sampled more than four and five years after the biochar have been applied to the fields on Umbrisol and Stagnosol, respectively. No significant effect of biochar or fertilizer treatments or their interactions were found on earthworms communities, suggesting biochar to be a safe method for carbon sequestration in Southern Finland conditions. The composition of earthworm species was typical for Finnish agricultural land with A. caliginosa dominating in both soils. However further research on long-term experiments are needed, in order to fully understand mechanisms of biochar effects on earthworms.