Biochar Feedstock Research Articles

Effects of biochar addition on chemical properties of a sandy soil from northeast Brazil

The application of biochar in soils is a well-established strategy to improve their physical and chemical properties, but the effects should be evaluated for each soil particularly. This study was conducted in a greenhouse of the Agricultural Sciences Unit (ASU) of Rio Grande do Norte Federal University (UFRN), in Macaiba, RN, Brazil, to evaluate the effect of biochar addition to sandy soil. The experiment was carried out in 10-L pots in a completely randomized design with four doses of biochar (0, 3500, 7000, and 10,500 kg ha−1) and four replications. The soil was collected from the top layer of a field adjacent to ASU and the biochar feedstock was wood from pruning cashew trees. The pots were cultivated with upland rice (Oryza sativa L.) and cowpea (Vigna unguiculata (l.) Walp.) in succession. The soil was sampled at 150 and 220 days after application of the treatments. The soil variables determined were pH, soil organic matter, contents of phosphorous (P), potassium (K), and calcium (Ca) plus magnesium (Mg), in addition to cation exchange capacity and exchangeable sodium percentage. Statistical analysis of experimental data included analysis of variance of the effect of biochar and regression analysis for variables with significant effect of those doses. The biochar obtained from cashew tree wood used in the experiment showed potential for use as a soil conditioner, since pH and K and P contents increased with rising doses of biochar. However, using this type of biochar can pose a risk regarding salinization, as indicated by the increase in exchangeable sodium percentage (ESP).

Using Industrial Sewage Sludge-Derived Biochar to Immobilize Selected Heavy Metals in a Contaminated Calcareous Soil

Many studies have indicated the effect of biochar on the fractionation of heavy metals in acidic soils, while little information is available on their effects on contaminated calcareous soils. Applying biochar products from sewage sludge pyrolysis as soil amendment was investigated in this study with special attention paid to fractionation of Pb and Cd in calcareous soil around a lead–zinc mine when pyrolysis temperature and biochar application rates were changed. The biochar feedstock was industrial sewage sludge, collected from the Baharan industrial park, using an anaerobic–anoxic–aerobic treatment process at two different temperatures (300 and 600 °C), and then adopted as amendment for the soil. The results revealed that with increasing pyrolysis temperature, the biochar’s levels of N, H and O decreased, while its amount of C increased significantly. The highest rate of the biochar application (8%) had lower pH compared to the control soil for both biochars. The soil EC with 8% biochar 300 °C was less than biochar 600 °C, perhaps due to the higher amount of ash in the biochar produced at 600 °C. The results showed that biochar 600 was more porous than biochar 300. The exposed porous structure made the pores more accessible for the adsorbate particles. Therefore, the biochar produced at 600 °C, more effectively, reduced the exchangeable form of Pb and Cd. The organic forms of Pb and Cd increased with increasing levels of biochar application, and this trend was higher in the treated soil with biochar produced at 600 °C due to high organic carbon content. The results showed that most of Pb and Cd existed in the residual form after application of biochar, especially at 600 °C, resulting in a significant reduction in their bioavaliability.

Assessment of Physicochemical and Nutritional Characteristics of Waste Mushroom Substrate Biochar under Various Pyrolysis Temperatures and Times

The prime objective of biochar production is to contribute to nutrients recycling, reducing waste and converting useful bio-wastes into carbon rich products in the environment. The present study was intended to systematically evaluate the effect of pyrolysis conditions and characteristics of feedstock influencing the generation of biochar. The study revealed the nutritional importance of waste mushroom substrate (WMS) biochar which may elevate soil nutritional status and soil quality. The results showed that the yields and properties of WMS biochar depended principally on the applied temperature where pyrolysis at higher temperatures, that is, 600 °C and 700 °C produced biochar having high ash, P and K contents. Moreover, numerous useful macro and micro nutrients such as Ca, Mg, Fe and Zn were observed to positively correlate with the increase in temperature. The WMS biochar in our study is highly alkaline which can be used to rectify acidic soil pH. Overall our results suggest that WMS biochar being a rich source of nutrients can be the best remedy to maintain and further enhance the soil nutritional status. Thus by interpreting biochar feedstock characteristics and pyrolysis conditions, the regulation of tailored WMS biochar manufacturing and application in soil can be facilitated.

Biochar and Water Quality.

Biochar application is considered to be an emerging strategy to improve soil ecosystem services. However, implications of such application on water quality parameters have not been widely discussed. This paper synthesizes the state-of-the-art research on biochar effects on water erosion, nitrate leaching, and other sources of water pollution. Literature indicates that in general, biochar application reduces runoff by 5 to 50% and soil loss by 11 to 78%, suggesting that it can be effective at reducing water erosion, but the magnitude of erosion reduction is highly variable. Co-application of biochar with other organic amendments (i.e., animal manure, compost) appears to be more effective at reducing water erosion than biochar alone. A main mechanism by which biochar can reduce water erosion is by improving soil properties (i.e., organic C, hydraulic conductivity, aggregate stability), which affect soil erodibility. This review also indicates that biochar reduces nitrate leaching, in most cases by 2 to 88%, but has mixed effect on phosphate and dissolved C leaching. Additionally, biochar effectively filters urban runoff, adsorbs pollutants, and reduces pesticides losses. Biochar feedstock, pyrolysis temperature, application amount, time after application, and co-application with other amendments affect biochar impacts on water quality. Biochar erosion and potential reduction in nutrient and pesticide use efficiency due to the strong adsorption are concerns that deserve consideration. Overall, biochar application has the potential to reduce water erosion, nitrate leaching, pesticide losses, and other pollutant losses, but more field-scale data are needed to better discern the extent to which biochar can improve water quality.

Degradation of imazapic and imazapyr herbicides in the presence of optimized oil palm empty fruit bunch and rice husk biochars in soil.

Imidazolinones as a persistent and active herbicides group have potential risks to non-target organisms in the environment. Biochar is a carbon-rich sorbent used as an amendment to change soil properties and its microbial communities effective on pesticides degradation rate. The present study was the first to compare empty fruit bunch (EFB) of oil palm and rice husk (RH) biomasses as biochar feedstock for remediation of imidazolinones-contaminated soils. Degradations of imazapic, imazapyr, and a mixture of them (Onduty®) was investigated in the presence of the optimized biochars in the soil during a 70-days incubation. Based on the results, the polar herbicides were resistant to hydrolysis degradation. Photolysis rates of the herbicides reduced significantly in the presence of the biochars in the soil. EFB biochar had greater effects due to its chemical compositions and surface functional groups. Photo-degradation of imazapyr was more affected by biochars amendment. The imidazolinones bio-degradation, however, accelerated significantly with the presence of EFB and RH biochars in soil with the greater effects of RH biochar. It was concluded that the application of the optimized EFB and RH biochars as an innovative sustainable strategy has the potential to decrease the persistence of the imidazolinones and minimize their environmental hazards.

The Utilization Of Some Of Biochar To Retain N-Total In Inceptisols

Nitrogen is very important nutrient growth of plant but eassy lost from soil. The aim of this researc to get the best biochar feedstock in maintaining N-total in the Inceptisol soil. Theresearch was carried out in the laboratory using the method of experiment. This research was carried out with complete randomized design non factorial with the treatment without biochar (controls), and 4 types of biochar from palm empty fruit bunches, rice straw, rice husks and wood, is repeated four times. The observed parameters are pH H2O,CEC, & N-total ground. The results showed that the four types of biochar can increase the pH H2O, CEC, N-total ground. Loss of Nutrient N decreased significantly due to the granting of biochar palm empty fruit bunches. Absorption capacity of biochar to reduce leaching of N in the soil of inseptisol sorted from largest to smallest is biochar palm empty fruit bunches, rice husk, rice straw and wood.

A comparison of drum granulation of biochars

ABSTRACT Drum granulation can be used to form biochar granules that could reduce dust hazards during biochar application to soils. An investigation of the effect of operational parameters using three biochar feedstock was conducted to identify the effect of biochar feedstock on granule properties. Cornstalk, birchbark and miscanthus biochar powders were successfully granulated and found to have varying granulation mechanisms, attributed primarily to differences in hydrophobic behaviour. Cornstalk granulated similarly to hydrophilic powders while birchbark had delayed granule nuclei formation resulting in larger nuclei. Miscanthus did not penetrate into the biochar powder and granulated through layering. All three operational parameters affected granule size. An increase in liquid volume and rotational speed increased the granule size of all three biochars. Binder concentration had a negative effect on granule growth due to viscous forces that decreased granule deformation. Granule strength was high for all three types of biochar granules and was affected by rotational speed of the drum and the liquid binder concentration. Increased binder concentration increased granule strength by promoting consolidation. Rotational speed of the drum had varying effects on granule strength due to differences in the granulation mechanisms of the biochars. The results demonstrate that multiple biochar feedstock can be granulated using wet drum granulation, but granulation parameters must be adjusted to produce granules with specified characteristics.

Linking feedstock and application rate of biochars to N2O emission in a sandy loam soil: Potential mechanisms

Biochar amendment has been proposed as a strategy to improve soil quality and mitigate climate change. Yet the extent and regulating mechanisms of soil nitrous oxide (N2O) emission in response to amendment of biochars derived from different feedstock have not been clearly demonstrated. A 12-month field trial was conducted to study the impact of two distinct biochar feedstocks (pine chip and peanut shell, at 10 and 30 t ha−1) with (+N) and without nitrogen (N) (−N) fertilization on soil N dynamics, N2O emissions, plant performance and microbial gene abundance. The cumulative N2O emissions varied greatly with biochar feedstock and application rate, and N fertilization. Pine biochar (at 30 t ha−1) significantly increased N2O emissions (by 48%) compared to control under −N, while peanut shell biochar (at 30 t ha−1) significantly increased N2O emissions (by 131%) compared to control under +N. Overall, biochar amendments had no impact on soil mineral N (NH4+ and NO3−) under both −N and +N. Under −N, biochar amendments showed no effect on plant yield, whereas under +N yield was significantly improved by 25–27% from pine biochar treatments. Under +N, only pine biochar (at 10 t ha−1) significantly increased plant N uptake (by 47%), and only peanut shell biochar (at 30 t ha−1) significantly enhanced soil AOB, narG, nirS and nosZ gene abundance. Increased soil N2O emission under −N from pine biochar amendment is likely to be regulated by improved water retention. However, increases in N2O emission from peanut shell biochar under +N could be driven by its large N inputs, labile organic C concentration and the increased soil pH which might largely facilitate biotic processes as evidenced by higher narG, nirS and AOB gene abundance. Positive feedback to N2O emission by biochar application revealed from this study is inconsistent with many current biochar studies, showing that caution should be exercised when considering use of biochar to mitigate N2O emission.

Cadmium (Cd) concentration in wheat (Triticum aestivum) grown in Cd-spiked soil varies with the doses and biochar feedstock

Biochar is considered a promising amendment for the reduction of metal concentration in plants; however, the effects of biochar in terms of dose and feedstock on metal uptake by plants remain widely unclear. In the current study, three individual biochars were prepared at 450 °C from different feedstocks (wheat straw, sukh chain (Pongamia pinnata), and cotton sticks). The main aim was to evaluate their ability to remediate cadmium (Cd)-spiked soil in terms of growth response and Cd uptake by wheat (Triticum aestivum) tissues. Biochars were separately applied at 0, 1, and 2% (w/w) in Cd-spiked soil and wheat was grown until maturity in pots and then morphological and physiological parameters and Cd concentrations in grains, roots, and shoots were determined. The post-harvest soil was analyzed for extractable Cd concentrations. Plants grown in Cd-spiked soil treated with biochars had higher seed germination, lengths of roots, shoots, and spikes, grains per spike and leaf relative water contents, chlorophyll contents, and dry weight of roots, shoots, and grains as compared to the untreated control. Biochar treatments significantly decreased the Cd concentrations in shoots, roots, and grains as well as total Cd uptake by grains. Soil extractable Cd concentrations were significantly decreased with biochar treatments. The application of 2.0% wheat straw biochar was the most efficient treatment in increasing grain yield and decreasing Cd in grains as well as soil extractable Cd than the other two biochars and doses applied.

Biochar addition to soil highly increases P retention and decreases the risk of phosphate contamination of waters

Phosphorus loss from agricultural soils is an important cause of eutrophication. The diversity of soil conditions and biochar feedstocks induces various effects on P retention after biochar application. Here, the effect of biochars at three application rates (0/1/5%, w/w) on P sorption and desorption in paddy soil with two levels of P application, 0 and 60 mg kg−1, were evaluated. Results show a notable reduction of the phosphorus activation coefficient (PAC, AP (available P)/TP (total P)) with biochar addition, thus suppressing the risk of P loss by the formation of Ca–P and Fe–P. The Langmuir sorption maximum (Qm) increased by 20.7–21.6%, 18.5–40.6% and 14.1–31.2% in amendments of biochar obtained from pig manure, corn straw and pine, respectively. The P sorption index (PSI) and maximum buffer capacity (MBC) in soils with biochar obtained from different feedstocks ranged in order from pig manure > corn straw > pine. Pig manure biochar had no significant effect on P retention due to changes in Ca/Mg/P by adjusting the pH, electronegativity and P content, resulting in anion repulsion. However, pine-derived biochar was favorable for the accumulation of thermally stable carbon dominated by aromatic carbon as well as lower alkalinity, promoting P sorption and suppressing P availability, especially at low P levels. In this study, we show that adding woody biochar to soil can simultaneously suppress nonpoint source pollution and reduce P fertilizer inputs.

Influence of soil properties and feedstocks on biochar potential for carbon mineralization and improvement of infertile soils

The impact of biochar (BC) application on soil varies with BC feedstock and soil type. The objective of this study was to investigate the linkage between the properties and surface functionality of various BCs and their role in the rehabilitation of two infertile soils. Sandy loam (SL) and sandy (S) soils were collected from agricultural areas in Korea and Vietnam, respectively. The BCs of amur silvergrass residue (AB), paddy straw (PB), and umbrella tree (UB) were applied to the soils at a rate of 30 t ha−1 and incubated at 25 °C for 90 d. Soil carbon (C) mineralization was investigated by a periodic measurement of CO2 efflux. Soil texture strongly influenced the CO2 efflux more than the BC type as indicated by 2–4 folds increase in cumulative CO2-C efflux from the SL soil compared to that from the S soil. For the PB-, AB-, and UB-treated S soils, the values of cation exchange capacity (CEC) were increased by 906%, 180%, and 130%, respectively, compared to that of the control; however, for the PB-treated SL soil, only a 13% increase in CEC was found. The pH in the PB-treated S soil sharply increased by 4.5 units compared to that in the control, due to a high concentration of readily soluble compounds in the PB and the low buffering capacity of the S soil. The S soil was more sensitive to the addition of BCs than the SL soil. A more prominent improvement in soil fertility can be achieved by BC application to the sandy soil having low clay, nutrient, and organic matter contents.

The environmental characteristics and applications of biochar.

The environmental deterioration is in a grave situation, and it is urgent to restore the environment. Biochar is a carbon-rich pyrolysis product of feedstock, which has aroused extensive concern due to its broad application potential for getting rid of pollutants and rehabilitating environment. This review generalizes three aspects on biochar, including production and properties, applications and mechanisms, and its modifications. Firstly, the production and characteristics have been summarized, because the practical applications of biochar are highly related to the special characteristics of biochar. Secondly, this paper outlines the latest applications of biochar for environmental remediation, and further provides a critical review on the application mechanisms in environmental restoration. Thirdly, the modification methods and applications of modified biochar are summarized, and all of the ways can be classified into two types: pretreatment of feedstock and modification of primitive biochar. Furthermore, the possible improvements and outlooks of applying biochar in environmental remediation are proposed. This review provides useful information for the application of biochar in environmental restoration.

Biochar feedstock and pyrolysis temperature effects on leachate: DOC characteristics and nitrate losses from a Brazilian Cerrado Arenosol mixed with agricultural waste biochars

Dissolved organic carbon (DOC) leached from Brazilian Cerrado Arenosols can lead to carbon (C) losses and lower soil fertility, while excessive nutrient, e.g. nitrate (NO3−), leaching can potentially cause water contamination. As biochar has been shown to stabilize C and retain soil nutrients, a greenhouse experiment was conducted to test different biochars’ contributions to DOC and NO3− leaching from a sandy soil. Biochars were made from four local agricultural waste feedstocks (cotton residue, swine manure, eucalyptus sawmill residue, sugarcane filtercake) pyrolysed at 400, 500 and 600 °C. Biochar was mixed with soil at 5% weight in pots and maize seeds planted. Leachate was collected weekly for six weeks and analyzed for DOC and NO3− concentrations, while fluorescence spectroscopy with parallel factor analysis (PARAFAC) was used to interpret DOC characteristics. Cotton and swine manure biochar treatments had higher DOC and NO3− losses than eucalyptus biochar, filtercake biochar, and control treatments. Cotton and swine manure biochar treatments at high temperatures lost mostly terrestrial, humified DOC, while swine manure, filtercake, and eucalyptus biochars at low temperatures lost mostly labile, microbially-derived DOC. Through the practical use of fluorescence spectroscopy, our study identified filtercake and eucalyptus biochars as most promising for retaining DOC and NO3− in a Cerrado Arenosol, potentially reducing stable C and nutrient losses.

The effect of biochar feedstock, pyrolysis temperature, and application rate on the reduction of ammonia volatilisation from biochar-amended soil

Ammonia (NH3) volatilisation is one of the most important causes of nitrogen (N) loss in soil-plant systems worldwide. Carbon-based amendments such as biochar have been shown to mitigate NH3 volatilisation in agricultural soils to various degrees. In this study, we investigated the influence of biochar feedstocks (poultry manure, green waste compost, and wheat straw), pyrolysis temperatures (250, 350, 450, 500 and 700°C) and application rates (1 and 2%), on NH3 volatilisation from a calcareous soil. The 15 biochars were chemically characterized, and a laboratory incubation study was conducted to assess NH3 volatilisation from the soil over a period of four weeks. Furthermore, changes to the bacterial and fungal communities were assessed via sequencing of phylogenetic marker genes.The study showed that biochar feedstock sources, pyrolysis temperature, and application rates all affected NH3 volatilisation. Overall, low pyrolysis temperature biochars and higher biochar application rates achieved greater reductions in NH3 volatilisation. A feedstock related effect was also observed, with poultry manure biochar reducing NH3 volatilisation by an average of 53% in comparison to 38% and 35% reductions for biochar from green waste compost and wheat straw respectively. Results indicate that the biogeochemistry underlying biochar-mediated reduction in NH3 volatilisation is complex and caused by changes in soil pH, NH3 sorption and microbial community composition (especially ammonia oxidising guilds).

Does biochar affect the availability and chemical fractionation of phosphate in soils?

Biochar as a soil amendment has been reported to affect the content and availability of soil nutrients. In this study, we aimed to test whether the biochar addition to soils would change the availability and chemical fractionation of phosphate in soils. Two soils (Ultisol and Alfisol) were amended with five kinds of biochars at application rate of 0, 1, and 2% (w/w). After 3-month incubation, availability and chemical forms of P were measured to investigate the potential effect and role of biochar in improving P availability in soils. The biochars used here had a lager variation of P content, depending on their feedstocks. Compared to the untreated soils, application of biochars derived from deciduous tree leaves (DLB), reed (RB), and rice straw (RSB) significantly increased the pH of two soils. The total P content of biochar-amended soils was increased with the addition of biochars. However, only RSB exhibited a significant increase (p < 0.05) of total P content. Application of biochars significantly increased the NH4Cl-extractable P content of two soils, indicating that biochars were able to increase the availability of phosphate in soils, but the amount of available P was dependent on biochar types. Ultisol and Alfisol amended with RSB (2% w/w) showed an increase in the P availability (0.5M NaHCO3-extractable P) by 46 and 39%, respectively. For strongly acidic Ultisol, addition of biochar significantly increased Al-P and Ca-P content, as well as decreased Fe-P content. The P desorption test indicated the release of P from soils increased with the addition of biochar. Results suggested that biochar would change the P sorption affinity of the soil and help to increase the availability of fixed P. The increase of P availability with biochar application was due to the pH change and direct P contribution from biochar. Our results concluded that biochar affected the availability, chemical forms, and sorption capability of phosphate in soil. The extent of biochar effects on soil P varied greatly with the type of feedstock of biochar and soil type.

Biochar application for the remediation of heavy metal polluted land: A review of in situ field trials

Polluted land is a global issue, especially for developing countries. It has been reported that soil amendment with biochar may reduce the bioavailability of a wide range of contaminants, including heavy metal(loids), potentially reclaiming contaminated soils for agricultural use. However, there have been only limited reports on the in situ application of biochar at the field scale. This review was devoted to providing preliminary scientific evidence from these field trials, based on a review of 29 publications involving field applications of biochar in 8 different countries. The data show that biochar's effectiveness in reducing the impacts of pollution depends on a myriad of factors in the field, including the application time period, site-specific factors (e.g. climate, biochar dosage rate, and mixing depth), biochar feedstock type, and biochar properties. The results of this review indicate that biochar application can potentially reduce contaminant bioavailability in the field; for instance, a significant decrease (control normalized mean value=0.55) in the Cd enrichment of rice crops was observed. It was found that the use of biochar may help increase crop yields on polluted land, and thus reduce the amount of mineral fertilizer used in the field. However, in order to maximize the benefits of biochar addition, farmers need to accept that the dosage rates of mineral fertilizers should be reduced. This review also revealed that the effectiveness of biochar in mitigating pollution may decrease with time due to ageing factors, such as leaching of biochar alkalinity.

Assisted phytostabilization of a multicontaminated mine technosol using biochar amendment: Early stage evaluation of biochar feedstock and particle size effects on As and Pb accumulation of two Salicaceae species (Salix viminalis and Populus euramericana)

Soil contamination by metal(loid)s is one of the most important environmental problem. It leads to loss of environment biodiversity and soil functions and can have harmful effects on human health. Therefore, contaminated soils could be remediated, using phytoremediation. Indeed, plant growth will improve soil conditions while accumulating metal(loid)s and modifying their mobility. However, due to the poor fertility and high metal(loid)s levels of these soils, amendments, like biochar, has to be applied. This study was performed on a former mine technosol contaminated by As and Pb and aimed to study (i) the effect of biochar on soil physico-chemical properties and plant phytostabilization potential (ii) biochar feedstock and particle size effects. In this goal, a mesocosm experiment was set up using four different biochars, obtained from two feedstocks (lightwood and pinewood) and harboring two particle sizes (inf. 0.1 mm and 0.2–0.4 mm) and two Salicaceae species. Soil and soil pore water physico-chemical properties as well as plant growth and metal(loid)s distribution were assessed. The results showed that biochar was efficient in improving soil physico-chemical properties and reducing Pb soil pore water concentrations. This amelioration allowed plant growth and increased dry weight production of both species. Regarding metal(loid)s distribution, willow and poplar showed an As and Pb accumulation in roots and low translocation towards edible parts, i.e stems and leaves, which shows a phytostabilization potential. Finally, the 2 biochar parameters, feedstock and particle size, only affected soil and soil pore water physico-chemical properties while having no effect on plant growth.

Effects of biochar addition on toxic element concentrations in plants: A meta-analysis

Consuming food contaminated by toxic elements (TEs) could pose a substantial risk to human health. Recently, biochar has been extensively studied as an effective soil ameliorant in situ because of its ability to suppress the phytoavailability of TEs. However, despite the research interest, the effects of biochar applications to soil on different TE concentrations in different plant parts remain unclear. Here, we synthesize 1813 individual observations data collected from 97 articles to evaluate the effects of biochar addition on TE concentrations in plant parts. We found that (1) the experiment type, biochar feedstock and pyrolysis temperature all significantly decreased the TE concentration in plant parts; (2) the responses of Cd and Pb concentrations in edible and indirectly edible plant parts were significantly more sensitive to the effect of biochar than the Zn, Ni, Mn, Cr, Co and Cu concentrations; and (3) the biochar dosage and surface area, significantly influenced certain TE concentrations in plant tissues as determined via correlation analysis. Moreover, the only exception in this study was found for metalloid element (i.e., As) concentrations in plants, which were not significantly influenced by biochar addition. Overall, the effects of biochar on TE concentrations in plant tissues were negative, at least on average, and the central trends suggest that biochar has a considerable ability to mitigate the transfer of TEs to food, thereby reducing the associated health risks. Our results provide an initial quantitative determination of the effects of biochar addition on multifarious TEs in different plant parts as well as an assessment of the ability of biochar to reduce TE concentrations in plants.

The influence of particle size and feedstock of biochar on the accumulation of Cd, Zn, Pb, and As by Brassica chinensis L.

Biochar produced from rice straw (RC) and maize stalk (MC) was amended to the heavy metal-contaminated soil to investigate the effects of different biochar feedstock and particle size (fine, moderate, coarse) on the accumulation of Cd, Zn, Pb, and As in Brassica chinensis L. (Chinese cabbage). The concentrations of Cd, Zn, and Pb in shoot were decreased by up to 57, 75, and 63%, respectively, after biochar addition (4%). Only MC decreased As concentration in B. chinensis L. shoots by up to 61%. Biochar treatments significantly decreased NH4NO3-extractable concentrations of Cd, Zn, and Pb in soil by 47-62, 33-66, and 38-71%, respectively, yet increased that of As by up to 147%. Amendment of RC was more effective on immobilizing Cd, Zn, and Pb, but mobilizing soil As, than MC. A decrease in biochar particle size greatly contributed to the immobilization of Cd, Zn, and Pb in soil and thereby the reduction of their accumulations in B. chinensis L. shoots, especially RC. Increases in soil pH and extractable P induced by biochar addition contributed to the sequestration of Cd, Zn, and Pb and the mobilization of As. Shoot biomass, root biomass, and root system of B. chinensis L. were enhanced with biochar amendments, especially RC. This study indicates that biochar addition could potentially decrease Cd, Zn, Pb, and As accumulations in B. chinensis L., and simultaneously increase its yield. A decrease in biochar particle size is favorable to improve the immobilization of heavy metals (except As). The reduction in Cd, Zn, Pb, and As levels in B. chinensis L. shoots by biochar amendment could be mainly attributed to a function of heavy metal mobility in soil, plant translocation factor, and root uptake.

Effect of feedstock and pyrolysis temperature on properties of biochar governing end use efficacy

The aim of this study was to systemically evaluate how feedstock characteristics and temperature influence biochar evolution during pyrolysis and to establish their relationships with biochar potential for soil amendments. We produced four biochar thermosequences from oak, pine, sugarcane and peanut shell at twelve temperatures (350–900 °C), and characterised them by yield, proximate analysis, elemental analysis, pH, electrical conductivity (EC) and carbon (C) functional groups using FTIR and solid-state 13C CPMAS NMR spectroscopy, along with principal component and cluster analyses. The results showed that not all biochar properties changed consistently with increasing pyrolysis temperature during slow pyrolysis. The significant increase in biochar pH with increasing pyrolysis temperature, was only observed between 350 and 500 °C (p < 0.05). Three principal components (PC) explained 88.9% of the variances in biochars. PC1 (ash, Mn, K, Fe, N, P and EC) and PC3 (Ca, Na and Mg) scores were essentially determined by feedstock type with notable influence of low pyrolysis temperatures. PC2 (O, H, C, volatile matter, fixed matter and pH) score was greatly influenced by pyrolysis temperature. Sugarcane derived biochars had high PC1 score but low PC3 score, while peanut shell derived biochars were contributed by both PC1 and PC3. The wood derived biochars had low scores of both PC1 and PC3, but the low temperature end of wood derived biochar thermosequences had significant higher PC2 scores than the high temperature end (p < 0.05). Understanding how biochar feedstock characteristics and pyrolysis temperature regulate biochar evolution will benefit tailored biochar manufacture.