Impact of Biochar on Earthworm Populations: A Review

Abstract

Despite the overwhelming importance of earthworm activity in the soil system, there are a limited number of studies that have examined the impact resulting from biochar addition to soil. Biochar is part of the black carbon continuum of chemothermal converted biomass. This review summarizes existing data pertaining to earthworms where biochar and other black carbon substances, including slash-and-burn charcoals and wood ash, have been applied. After analyzing existing studies on black carbon, we identified that these additions have a range from short-term negative impacts to long-term null effects on earthworm population density and total biomass. Documented cases of mortality were found with certain biochar-soil combinations; the cause is not fully understood, but hypothesized to be related to pH, whether the black carbon is premoistened, affects feeding behaviors, or other unknown factors. With wood ashes, negative impacts were overcome with addition of other carbon substrates. Given that field data is limited, soils amended with biochar did not appear to cause significant long-term impacts. However, this may indicate that the magnitude of short-term negative impacts on earthworm populations can be reduced with time.

Crop residue decomposition in Minnesota biochar-amended plots

“…Macrofaunal activity was evident at the field plots, in particular as visible surface earthworm activity and castings. However, a macrofaunal sampling established that earthworm abundance was not significantly different at the time of litterbag placement (Weyers and Spokas, 2011). This would be in agreement with other studies illustrating shortterm impacts on macrofaunal activity observed in short-term laboratory studies (i.e., months) Marks et al, 2014), but these short-term effects are not persistent in the field .…”

Biochar: Pyrogenic Carbon for Agricultural Use - A Critical Review

“…Seemingly, the main impact caused by biochar on earthworms is due to pH, which can change responses according to the biochar application time (Weyers and Spokas, 2011).…”

Influence of Various Biochars on the Survival, Growth, and Oxidative DNA Damage in the Earthworm Eisenia Fetida

“…Nevertheless, the harmful materials released from pyrolyzed BC unintentionally may inhibit the soil organisms (Lehmann et al, 2011;Weyers and Spokas, 2011). Pyrolyzed BCs contain toxic metal(loid)s, PAHs, and dioxins with various isomers, which are associated with oxidative stress through accumulation of reactive oxygen stress (ROS) in cellular tissues (Stegeman and Lech, 1991;Lopez et al, 2006).…”

“…Greater concentrations of 8-OHdG were observed by Li et al (2011) in soil amended with BC produced from woodchips at 550℃ than 300℃. The BCs pyrolyzed over 500℃ contain high concentrations of trace metal(loid)s, which are known to cause oxidative stress in earthworms (Weyers and Spokas, 2011).…”