Designing amendments to improve plant performance for mine tailings revegetation.

To provide recommendations for establishment of plants on low-pH Formosa Mine tailings, two greenhouse experiments were conducted to evaluate the use of remedial amendments to improve the survival and growth of Douglas fir (Pseudotsuga menziesii) seedlings. A preliminary experiment indicated that 1% lime (by weight) raised tailings pH, permitting seedling survival. However, high rates of biosolid application (BS; 2% by weight) added to supply nutrients were phytotoxic when added with lime. A gasified conifer biochar (BC) added to tailings at 1%, 2.5%, or 5% (by weight), along with lime and BS, caused an additional increase in pH, decreased electrical conductivity (EC), and tended to increase the survival of Douglas fir. The addition of a locally sourced microbial inoculum (LSM) did not affect survival. A subsequent experiment expanded our experimental design by testing multiple levels of amendments that included lime (0.5% and 1% by weight), three application rates (0.2%, 0.5%, and 2%) of two nutrient sources (BS or mineral fertilizer), BC (0% and 2.5%), and with or without LSM. There were many interactions among amendments. In general, Douglas fir survival was enhanced when lime and BC were added. These experiments suggest that amending with lime, a nutrient source, and BC would enhance revegetation on low-pH, metal-contaminated mine tailings.

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 run-off. 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 Mg3(PO4)2 phases while increasing temperature favored the formation of both Mg3(PO4)2 and Ca5(PO4)3OH. 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 PL-derived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.

Microbial Response to Phytostabilization in Mining Impacted Soils Using Maize in Conjunction with Biochar and Compost.

Even after remediation, mining impacted soils can leave behind a landscape inhospitable to plant growth and containing residual heavy metals. While phytostabilization can be used to restore such sites by limiting heavy metal spread, it is reliant on soil capable of supporting plant growth. Manure-based biochars, coupled with compost, have demonstrated the ability to improve soil growth conditions in mine impacted soils, however there is a paucity of information regarding their influence on resident microbial populations. The objective of this study was to elucidate the impact of these soil amendments on microbial community structure and function in mine impacted soils placed under phytostabilization management with maize. To this aim, a combination of phospholipid fatty acid (PLFA) and enzymatic analyses were performed. Results indicate that microbial biomass is significantly increased upon addition of biochar and compost, with maximal microbial biomass achieved with 5% poultry litter biochar and compost (62.82 nmol g-1 dry soil). Microbial community structure was impacted by biochar type, rate of application, and compost addition, and influenced by pH (r2 = 0.778), EC (r2 = 0.467), and Mg soil concentrations (r2 = 0.453). In three of the four enzymes analyzed, poultry litter biochar treatments were observed with increased activity rates that were often significantly greater than the unamended control. Overall, enzyme activities rates were influenced by biochar type and rate, and addition of compost. These results suggest that using a combination of biochar and compost can be utilized as a management tool to support phytostabilization strategies in mining impacted soils.

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. In order to improve soil conditions and encourage successful site revegetation, our study employed three biochars, sourced from different feedstocks (poultry litter, beef lot manure, and lodge pole 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 lot 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 for ß-glucosidase, N-acetyl-ß-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 Affects Essential Nutrients of Carrot Taproots and Lettuce Leaves.

Essential nutrient concentrations in crops can affect human health. While biochar has the potential as a soil amendment to improve crop yields, it may also affect the concentrations of nutrients such as Ca, Fe, K, Mg, Mn, and Zn in edible portions of crops. To better characterize effects of biochar on important human nutrients in food crops, we evaluated the effects of biochar on lettuce (Lactuca sativa L. cv. Black-Seeded Simpson) leaf and carrot [Daucus carota subsp. sativus (Hoffm.) Schübl. cv. Tendersweet] developing taproot nutrients. Plants were grown in pots in a greenhouse using sandy loam (Coxville, fine, kaolinitic, thermic Typic Paleaquults) and loamy sand (Norfolk, fine-loamy, kaolinitic, thermic Typic Kandiudults,) series soils, amended with biochar produced from four feedstocks: pine chips (PC), poultry litter (PL), swine solids (SS), and switchgrass (SG); and two blends of PC plus PL [Pc/PL, 50%/50% (55) and 80%/20% (82) by weight]. Biochar was produced at 350, 500, and 700 °C from each feedstock. Lettuce leaf and carrot taproot total nutrient concentrations were determined by inductively coupled plasma analysis. Biochar (especially at least in part manure-based, i.e., PL, SS, 55, and 82 at nearly all temperatures) primarily decreased nutrient concentrations in lettuce leaves, with Ca, Mg, and Zn affected most. Carrot taproot nutrient concentrations also deceased, but to a lesser extent. Some biochars increased leaf or taproot nutrient concentrations, especially K. This study indicated that biochar can both decrease and increase leaf and taproot nutrient concentrations important for human health. Thus, potential effects on nutrients in plants should be carefully considered when biochar is used as a soil amendment with vegetable crops.

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 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% (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 H2O- and 0.01 M CaCl2-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 H2O- and 0.01 M CaCl2-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.

Remediation of an acidic mine spoil: Miscanthus biochar and lime amendment affects metal availability, plant growth, and soil enzyme activity.

Biochar may be a tool for mine spoil remediation; however, its mechanisms for achieving this goal remain unclear. In this study, Miscanthus (Miscanthus giganteus) biochar was evaluated for its ability to reclaim acidic mine spoils (pH < 3) through reducing metal availability, improving soil microbial enzymatic activity, and initial growth of grass seedlings. Biochar was applied at 0, 1, 2.5 and 5% (w/w) along with lime/no lime and fertilizer additions. Blue Wildrye (Elymus glaucus cv. 'Elkton') was planted and later the shoots and roots were collected and metal concentrations determined. Afterwards, each pot was leached with deionized water, and the leachate analyzed for pH, electrical conductivity (EC), dissolved organic carbon (DOC) and soluble metal concentrations. After drying, the spoil was extracted with 0.01 M CaCl2 and Mehlich 3 (M3) to determine extractable Al, Cu, and Zn concentrations. Additionally, microbial activity was measured using a fluorescent ß-glucosidase and N-acetyl-ß-d-glucosaminidase assay. Spoil treated with lime and biochar had significantly greater pH and EC values. Significantly greater ß-glucosidase activity occurred only in the 5% biochar plus lime treatment, while N-acetyl-ß-d-glucosaminidase activities were not altered. Metal concentrations in rye shoot and roots were mixed. Lime additions significantly reduced extractable metal concentrations. Increasing biochar rates alone significantly reduced leachate DOC concentrations, and subsequently reduced leachable metal concentrations. Surprisingly, miscanthus biochar, by itself, was limited at mitigation, but when combined with lime, the combination was capable of further reducing extractable metal concentrations and improving ß-glucosidase enzyme activity.

A Rapid-Test for Screening Biochar Effects on Seed Germination.

We developed a rapid-test to screen for effects of biochar on seed germina- tion and soils. Crop seeds were placed in containers and covered with 15 g of soil with 1% biochar by weight. Two agricultural soils from South Carolina USA were used. Eighteen biochars were produced from six primary feedstocks [pine chips (PC), poultry litter (PL), swine solids (SS), switchgrass (SG); and two blends of PC and PL, 50% PC/50% PL (55), and 80% PC/20% PL (82)]. Each feedstock was pyrolyzed at 350, 500 and 700°C. There were few biochar effects on seed germination. Shoot dry weight was increased for carrot, cucumber, lettuce, oat, and tomato; primarily with biochars containing PL. Soil pH, electrical conductivity and extractable phosphorus primarily increased with PL, SS, 55, and 82 treatments for both soil types and across species. This method can be an early indicator of biochar effects on seed germination and soil health.

Organic amendments for risk mitigation of organochlorine pesticide residues in old orchard soils.

Performance of compost and biochar amendments for in situ risk mitigation of aged DDT, DDE and dieldrin residues in an old orchard soil was examined. The change in bioavailability of pesticide residues to Lumbricus terrestris L. relative to the unamended control soil was assessed using 4-L soil microcosms with and without plant cover in a 48-day experiment. The use of aged dairy manure compost and biosolids compost was found to be effective, especially in the planted treatments, at lowering the bioavailability factor (BAF) by 18-39%; however, BAF results for DDT in the unplanted soil treatments were unaffected or increased. The pine chip biochar utilized in this experiment was ineffective at lower the BAF of pesticides in the soil. The US EPA Soil Screening Level approach was used with our measured values. Addition of 10% of the aged dairy manure compost reduced the average hazard quotient values to below 1.0 for DDT + DDE and dieldrin. Results indicate this sustainable approach is appropriate to minimize risks to wildlife in areas of marginal organochlorine pesticide contamination. Application of this remediation approach has potential for use internationally in areas where historical pesticide contamination of soils remains a threat to wildlife populations.

Utilizing thin-film solid-phase extraction to assess the effect of organic carbon amendments on the bioavailability of DDT and dieldrin to earthworms.

Improved approaches are needed to assess bioavailability of hydrophobic organic compounds in contaminated soils. Performance of thin-film solid-phase extraction (TF-SPE) using vials coated with ethylene vinyl acetate was compared to earthworm bioassay (Lumbricus terrestris). A DDT and dieldrin contaminated soil was amended with four organic carbon materials to assess the change in bioavailability. Addition of organic carbon significantly lowered bioavailability for all compounds except for 4,4'-DDT. Equilibrium concentrations of compounds in the polymer were correlated with uptake by earthworms after 48d exposure (R(2) = 0.97; p < 0.001), indicating TF-SPE provided an accurate uptake simulation. Bioavailability of residues in soil was compared with a spiked soil aged for 90d in laboratory. Dieldrin and DDX were respectively 18% and 11% less bioavailable in contaminated soil relative to spiked soil despite >40yr of aging. Results show that TF-SPE can be useful in examining potential risks associated with contaminated soils and to test effectiveness of remediation efforts.

Selection of pecan shell-based activated carbons for removal of organic and inorganic impurities from water.

Activated carbons are a byproduct from pyrolysis and have value as a purifying agent. The effectiveness of activated carbons is dependent on feedstock selection and pyrolysis conditions that modify their surface properties. Therefore, pecan shell-based activated carbons (PSACs) were prepared by soaking shells in 50% (v/v) HPO or 25 to 50% of KOH-NaHCO followed by pyrolysis at 400 to 700°C under a N atmosphere. Physically activated PSACs were produced by pyrolysis at 700°C under N followed by activation with steam or CO at 700 to 900°C. Physicochemical, surface, and adsorption properties of the PSACs were compared with two commercially available activated carbons. The average mass yield of PSACs with respect to the initial mass of the biomass was about 20 and 34% for physically activated and chemically activated carbons, respectively. Acid-activated carbons exhibited higher surface area, higher bulk density, and lower ash content compared with steam- or CO-activated carbons and the two commercial products. Base activation led to the development of biochar with moderate to high surface area with surface charges suitable for adsorption of anionic species. Regardless of the activation method, PSACs had high total surface area ranging from 400 to 1000 m g, better pore size distribution, and more surface charges than commercial samples. Our results also showed that PSACs were effective in removing inorganic contaminants such as Cu and NO as well as organic contaminants such as atrazine and metolachlor. This study showed that pyrolysis conditions and activation had a large influence on the PSAC's surface characteristics, which can limit its effectiveness as a custom sorbent for targeted water contaminants.

Biochar: a synthesis of its agronomic impact beyond carbon sequestration.

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

Retention of heavy metals in a Typic Kandiudult amended with different manure-based biochars.

Although nutrient-rich manure biochars are expected to be an effective heavy metal stabilizer in agricultural and contaminated soils, systematic studies are lacking to predict the influence of manure variety and pyrolysis temperature on metal-binding potentials. In this study, biochars produced from five manure varieties (dairy, paved feedlot, swine solids, poultry litter, and turkey litter) at two pyrolytic temperatures (350 and 700°C) were examined for the stabilization of Pb, Cu, Ni, and Cd in a weathered, acidic Norfolk loamy sand (fine-loamy, kaolinitic, thermic, Typic Kandiudult). Equilibrium concentrations in the aqueous phase were determined for heavy metals (Cu, Ni, Cd, and Pb) and additional selected elements (Na, P, S, Ca, Mg, Al, and K); these were analyzed by positive matrix factorization to quantitatively determine the factors responsible for the biochar's ability to bind the selected heavy metals in soil. Concurrently with the greatest increase in pH and highest equilibrium Na, S, and K concentrations, poultry litter, turkey litter, and feedlot 700°C biochar exhibited the greatest heavy metal retention. In contrast, manure varieties containing disproportionately high (swine) and low (dairy) ash, P, and other elements were the least effective stabilizers. Regardless of the manure type, proton nuclear magnetic resonance analyses showed the removal of leachable aliphatic and nitrogen-containing heteroaromatic functional groups at the higher (700°C) pyrolysis temperature. Consistently greater Cu retention by the 700°C biochar indicated the mobilization of Cu by 350°C biochar-born dissolved organic carbon; however, the influence of other temperature-dependent biochar characteristics cannot be ruled out.

Impact of pyrolysis temperature and manure source on physicochemical characteristics of biochar.

While pyrolysis of livestock manures generates nutrient-rich biochars with potential agronomic uses, studies are needed to clarify biochar properties across manure varieties under similar controlled conditions. This paper reports selected physicochemical results for five manure-based biochars pyrolyzed at 350 and 700°C: swine separated-solids; paved-feedlot manure; dairy manure; poultry litter; and turkey litter. Elemental and FTIR analyses of these alkaline biochars demonstrated variations and similarities in physicochemical characteristics. The FTIR spectra were similar for (1) turkey and poultry and (2) feedlot and dairy, but were distinct for swine biochars. Dairy biochars contained the greatest volatile matter, C, and energy content and lowest ash, N, and S contents. Swine biochars had the greatest P, N, and S contents alongside the lowest pH and EC values. Poultry litter biochars exhibited the greatest EC values. With the greatest ash contents, turkey litter biochars had the greatest biochar mass recoveries, whereas feedlot biochars demonstrated the lowest.

Qualitative analysis of volatile organic compounds on biochar.

Qualitative identification of sorbed volatile organic compounds (VOCs) on biochar was conducted by headspace thermal desorption coupled to capillary gas chromatographic-mass spectrometry. VOCs may have a mechanistic role influencing plant and microbial responses to biochar amendments, since VOCs can directly inhibit/stimulate microbial and plant processes. Over 70 biochars encompassing a variety of parent feedstocks and manufacturing processes were evaluated and were observed to possess diverse sorbed VOC composition. There were over 140 individual chemical compounds thermally desorbed from some biochars, with hydrothermal carbonization (HTC) and fast pyrolysis biochars typically possessing the greatest number of sorbed volatiles. In contrast, gasification, thermal or chemical processed biochars, soil kiln mound, and open pit biochars possessed low to non-detectable levels of VOCs. Slow pyrolysis biochars were highly variable in terms of their sorbed VOC content. There were no clear feedstock dependencies to the sorbed VOC composition, suggesting a stronger linkage with biochar production conditions coupled to post-production handling and processing. Lower pyrolytic temperatures (⩽350°C) produced biochars with sorbed VOCs consisting of short carbon chain aldehydes, furans and ketones; elevated temperature biochars (>350°C) typically were dominated by sorbed aromatic compounds and longer carbon chain hydrocarbons. The presence of oxygen during pyrolysis also reduced sorbed VOCs. These compositional results suggest that sorbed VOCs are highly variable and that their chemical dissimilarity could play a role in the wide variety of plant and soil microbial responses to biochar soil amendment noted in the literature. This variability in VOC composition may argue for VOC characterization before land application to predict possible agroecosystem effects.

Long-term tillage effects on soil metolachlor sorption and desorption behavior.

Sorption and desorption are two important processes that influence the amount of pesticides retained by soils. However, the detailed sorption mechanisms as influenced by soil tillage management are unclear. This study examined the sorption and desorption characteristics of metolachlor [2-chloro-N-(2-ethyl-6-methyphenyl)-N-(2-methoxy-1-methylethyl)-acetamide] using the soil samples collected from the long-term conservation tillage (CnT) and conventional tillage (CT) research plots established in 1979 in Darlinton, SC. Humic acid (HA) and humin were extracted from the soils and used in the sorption experiments along with the whole soil samples. The sorption experiments were conducted using a batch-equilibration method. Three sequential desorption rinses were carried out following the sorption experiments. By comparing metolachlor sorption and desorption results we observed hysteresis for all soil samples and their organic matter fractions. Sorption nonlinearity (N) and hysteresis were dependent on the structure and composition of soil organic matter (SOM), e.g., Freundlich isotherm exponents (N) of HA and humin from CnT were higher than those of CT treatment, which may be related to high aromaticity of SOM fractions in CT treatment. Sorption capacity (K'f) was positively correlated with soil organic carbon (SOC) content. These results show that long-term tillage management can greatly affect metolachlor sorption and desorption behavior probably by qualitative differences in the structural characteristics of the humic substances.