Active removal of biochar by earthworms (Lumbricus terrestris)

摘要

The role earthworms play in the cycling of biochar in the soil column is poorly understood. While some studies show that earthworms favor a biochar-rich environment, they are ambiguous as to whether earthworms actively remove it and/or possibly consume it, or whether biochar indirectly provides a more favorable habitat. More importantly, associating the properties of different biochars to habitat preference by earthworms has received almost no attention. Courts were established with eight biochars from different feedstocks with varying in physicochemical properties. Circular piles (1.5 g) of biochar were applied to the surface of mesocosms containing field soil and 25 earthworms. Removal was quantified by digitally photographing the biochar samples and visually estimating disappearance over time. Most biochars were actively removed by the earthworms. The most preferred biochar was an aged biochar (>70 years) harvested from charcoal mounds, whereas the least preferred was a fast-pyrolysis biochar made from hardwood sawdust. There was an inverse relationship between the removal of biochar by earthworms and total carbon and a proportional increase with the contents of ash, Ca, Mn, and Si, although the correlations were not strong and may not explain earthworm preference. Other physicochemical properties of the biochars, such as the % volatile C, % H. porosity, and cumulative surface area, were associated with increased aerobic bacteria and fluorescent pseudomonads in soil, but not associated with biochar removal by earthworms. More research is needed to determine if tailoring specific biochars for surface removal by earthworms could be achieved by supplementing biochar with Ca, Mn, and Si and thus lead to a non-disruptive system for delivery of biochar into lower soil horizons of perennial crops. More importantly, this procedure may be useful in screening biochars for attractiveness to earthworms. (C) 2014 Elsevier GmbH. All rights reserved.