Biochar compost blends facilitate switchgrass growth in mine soils by reducing Cd and Zn bioavailability

Biochars have the potential to reclaim mine-impacted soils;however,their variable physico-chemical properties incite specu-lation about their successful remediation performance.This investigation examined the capability of biochars produced from three different feedstocks along with a compost blend to improve switchgrass growth conditions in a mine-impacted soil by examining influences on soil pH,grass metal contents,and soil-extractable metal concentrations.Cadmium(Cd)-and zinc(Zn)-contaminated mine soil was collected from a site near Webb City,Missouri,USA-a location within the Tri-State Min-ing District.In a full factorial design,soil was treated with a 0%,2.5%,and 5%(w/w)compost mixture(wood chips+beef cattle manure),and 0%,2.5%and 5%of each biochar pyrolyzed from beef cattle manure,poultry litter,and lodgepole pine feedstocks.Switchgrass(Panicum virgatum,‘Cave-In-Rock’variety)was grown in a greenhouse for 50 days and the mass of shoots(above-ground biomass)and roots was assessed,while soil pH,deionized H_(2)O-and 0.01 M CaCl_(2)-extractable Cd and Zn concentrations were measured.Poultry litter biochar and compost had the greatest ability to raise soil pH(from 4.40 to 6.61),beef cattle manure biochar and compost moderately raised pH(from 4.4 to 5.92),and lodgepole pine biochar and compost weakly raised pH(from 4.40 to 5.05).Soils treated with beef cattle manure biochar,poultry litter biochar signifi-cantly reduced deionized H_(2)O-and 0.01 M CaCl_(2)-extractable Cd and Zn concentrations,while lodgepole pine biochar-treated soils showed mixed results.Switchgrass shoot and root masses were greatest in soil treated with compost in combination with either beef cattle manure biochar or poultry litter biochar.Soils treated with 5%beef cattle manure biochar+5%compost had greater reductions in total Cd and Zn concentrations measured in switchgrass shoots and roots compared to the other two treatments.The three biochars and compost mixtures applied to heavy metal,mine-impacted soil had considerable performance dissimilarities for improving switchgrass productivity.Switchgrass growth was noticeably improved after treatment with the compost in combination with biochar from beef cattle manure or poultry litter.This may be explained by the increased soil pH that promoted Zn and Cd precipitation and organic functional groups that reduced soil-available heavy metal concentrations.Our results imply that creating designer biochars is an important management component in developing successful mine-site phytostabilization programs.

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.

Towards predicting biochar impacts on plant-available soil nitrogen content

Biochars can improve soil health but have been widely shown to reduce plant-available nitrogen(N)owing to their high carbon(C)content,which stimulates microbial N-immobilization.However,because biochars contain large amounts of C that are not microbially available,their total elemental C:N ratio does not correspond well with impacts on soil N.We hypothesized that impacts on soil plant-available N would relate to biochar mineralizable-C(C_(min))content,and that C:N ratios of the mineralizable biochar component could provide a means for predicting conditions of net soil N-mineralization or-immobilization.We conducted two laboratory experiments,the first measuring biochar C_(min)from respiration of isotopically labeled barley biochars manufactured at 300,500,and 750℃,and the second characterizing C_(min)by proxy measurements for ten biochars from six feedstocks at several temperatures.For both experiments,soils were incubated with 2%biochar by mass to determine impacts to soil N-mineralization.Contrary to expectation,all the biochars increased soil N-mineralization relative to unamended soils.Also unexpected,higher temperature(500 and 700℃)barley biochars with less C_(min)stimulated more soil decomposition and more soil N-mineralization than a 350℃barley biochar.However,across diverse biochar feedstocks and production methods,none of the biochar characteristics correlated with soil N-mineralization.The finding of improved soil N-mineralization adds complexity to the range of soil N responses that can be expected in response to biochar amendment.Because of the limited ability to predict soil N responses from biochar properties,users should monitor soil N to manage soil fertility.

Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar

Biochars with a high affinity for phosphorus(P)are promising soil amendments for reducing P in agricultural runoff.Poultry litter(PL)is an abundant biochar feedstock.However,PL-derived biochars are typically high in soluble P and therefore require chemical modification to become effective P sorbents.This study investigated the effect of magnesium(Mg)activation on extractable P(EP)and P sorption capacities of PL-derived biochars.Biochar was produced at 500-900°C from PL activated with 0-1 M Mg.Three differentially aged PL feedstocks were evaluated(1-,3-5-,and 7-9-year-old).Increased Mg activation level and pyrolysis temperature both resulted in EP reductions from the biochars.Specifically,biochars produced at temperatures≥700°C from PL activated with≥0.25 M Mg had negligible EP.X-ray diffractograms indicated that increased Mg loading favored the formation of stable Mg_(3)(PO_(4))_(2) phases while increasing temperature favored the formation of both Mg_(3)(PO_(4))_(2) and Ca_(5)(PO_(4))_(3)OH.Maximum P sorption capacities(Pmax)of the biochars were estimated by fitting Langmuir isotherms to batch sorption data and ranged from 0.66-10.35 mg g^(−1).Average Pmax values were not affected by PL age or pyrolysis temperature;however,biochars produced from 1 M Mg-activated PL did have significantly higher average Pmax values(p<0.05),likely due to a greater abundance of MgO.Overall,the results demonstrated that Mg activation is an effective strategy for producing PLderived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.