Microbial response to designer biochar and compost treatments for mining impacted soils

The Oronogo-Duenweg mining belt is a designated United States Environmental Protection Agency Superfund site due to lead-contaminated soil and groundwater by former mining and smelting operations.Sites that have undergone remediation-in which the O,A,and B horizons have been removed alongside the lead contamination-have an exposed C horizon and are incalcitrant to revegetation efforts.Soils also continue to contain quantifiable Cd and Zn concentrations.To improve soil conditions and encourage successful site revegetation,our study employed three biochars,sourced from different feedstocks(poultry litter,beef cattle manure,and lodgepole pine),at two rates of application(2.5%,and 5%),coupled with compost(0%,2.5%and 5%application rates).Two plant species-switchgrass(Panicum virgatum)and buffalograss(Bouteloua dactyloides)-were grown in the amended soils.Amendment of soils with poultry litter biochar applied at 5%resulted in the greatest reduction of soil bioavailable Cd and Zn.Above-ground biomass yields were greatest with beef cattle manure biochar applied at 2.5%with 5%compost,or with 5%biochar at 2.5%and 5%compost rates.Maximal microbial biomass was achieved with 5%poultry litter biochar and 5%compost,and microbial communities in soils amended with poultry litter biochar distinctly clustered away from all other soil treatments.Additionally,poultry litter biochar amended soils had the highest enzyme activity rates forβ-glucosidase,N-acetyl-β-D-glucosaminidase,and esterase.These results suggest that soil reclamation using biochar and compost can improve mine-impacted soil biogeophysical characteristics,and potentially improve future remediation efforts.

Biochar insights from laboratory incubations monitoring O_(2) consumption and CO_(2) production

Biochar has been touted as a long-term carbon sequestration tool.However,there are no studies evaluating biochar’s effect on oxygen(O_(2))consumption as a measure of the microbial respiration response to biochar.To gain insight into this aspect,we evaluated O_(2) consumption rates to test the hypothesis that biochar is an efficient agent for carbon dioxide(CO_(2))sequestration in soils.Four different biochar types and one activated charcoal were incubated alone and associated with three different soils for approximately 2 months in laboratory incubations.Headspace concentration of CO_(2) and O_(2) was periodically quantified.The data presented here confirm that the CO_(2) production following biochar’s addition to soils results in a process that is correlated to oxygen consumption.However,this overall stimulation is not clearly related to biochar type.Activated carbon resulted in the highest statistically significant stimulation of activity,despite it possessing the lowest quantity of volatile carbon and mineral nutrient sources.Taking into consideration our results,we conclude that using biochar does achieve total carbon sequestration.However,the amount of available soil organic carbon following soil incorporation appears to be reduced following biochar addition and its long-term implication on this mineralizable soil organic carbon pool does deserve more research attention.