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Title: Impact of biochar on earthworm populations: A review

item Weyers, Sharon
item Spokas, Kurt

Submitted to: Applied and Environmental Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2011
Publication Date: 10/27/2011
Citation: Weyers, S.L., Spokas, K.A. 2011. Impact of biochar on earthworm populations: A review. Applied and Environmental Soil Science. DOI: 10.1155/2011/541592.

Interpretive Summary: Biochar, a black carbon, can be produced through chemo-thermal conversion of biomass as a co-product in a process that generates bioenergy. Biochar is being investigated for its ability to sequester carbon and provide nutrient resources if used as a soil amendment in agricultural systems. Some research suggests that biochar may have detrimental effects on soil organisms, particularly earthworms. The currently available literature was reviewed and effects of biochar on earthworms evaluated. Although biochar may have short-term negative impacts on earthworm populations and biomass, the available information suggests that there are no long-term negative effects from using biochar as a soil amendment. Caution is still necessary as the magnitude of potential negative effects, even if short-lived, on soil organisms with field application have not been determined. This report is a joint effort of scientists at the North Central Soil Conservation Research Lab, in Morris, Minnesota, and the Soil and Water Research Unit, in St. Paul, Minnesota, and contributes to the USDA Agricultural Research Service multi-location biochar and pyrolysis research initiative. The information made available will help guide further research on biochar and its effects on soil organisms. Farmers, scientists, and policy makers will benefit from the improved understanding of potential negative impacts of biochar. This understanding as well as guidance for future research will improve production and safe use of biochar products.

Technical 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 chemo-thermal 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 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 pre-moistened, affects on 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.