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

Authors: Novak, Jeffrey; IPPOLITO, JAMES - Colorado State University; Watts, Donald - Don; Sigua, Gilbert; Ducey, Thomas; JOHNSON, MARK - Environmental Protection Agency (EPA)

Submitted to: Biochar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2019
Publication Date: 4/5/2019
Citation: Novak, J.M., Ippolito, J.A., Watts, D.W., Sigua, G.C., Ducey, T.F., Johnson, M. 2019. Biochar compost blends facilitate switchgrass growth in mine soils by reducing Cd and Zn bioavailability. Biochar Journal. 1:97-114. https://doi.org/10.1007/s42773-019-00004-7.
DOI: https://doi.org/10.1007/s42773-019-00004-7

Interpretive Summary: Mining activities and ensuing disposal of waste products can have profound impacts on soil health characteristics (low pH, toxic heavy metals concentrations, etc.) where mine wastes are stored. Stabilizing mine tailings and mine-impacted soils with a ground cover is an important management practice because plants can minimize off-site movement of toxic metals and can add organic matter to improve soil chemical characteristics for better plant growth. Without treatment, these poor soil conditions are known to reduce ground cover establishment and influence the degree of site phytostabilization. Thus, in mine soil remediation project, various materials are often utilized as amendments to improve soil health characteristics. Current literature adjudicates the use of biochar as an amendment in mine reclamation sites, however, their difference in physical and chemical properties will influence their ability to react with toxic metals and improve soil chemical conditions. We conducted an experiment to determine the effectiveness of three different biochars produced from manures and wood feedstocks and compost blends with reducing the availability of toxic heavy metals to switchgrass. Mine-impacted soil was obtained from a EPA Superfund site known to contain high concentrations of cadmium (Cd) and zinc (Zn). We found that switchgrass growth was facilitated more by a manure-based biochar because they were able to reduce more water and bioavailable Cd and Zn concentrations in soil compared to a pine wood-based biochar.

Technical Abstract: Biochars have the potential to reclaim mine-impacted soils; however, their variable physico-chemical properties incite speculation 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 Mining District. In a full factorial design, soil was treated with a 0, 2.5, and 5% (weight/weight) 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 mass of shoots (above ground biomass) and roots were assessed, while soil pH, deionized water and calcium chloride 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 significantly reduced deionized water and 0.01 Molar calcium chloride 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 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.