Biochar Extracts Research Articles

Evaluating the impact of different biochar types on wheat germination.

This study assessed sustainable solutions for organic waste management, focusing on biochar derived from kitchen waste. The characteristics and phytotoxicity effects of biochar produced from four different types of kitchen waste were investigated in view of potential agricultural applications. Analysis of the chemical and physical properties of the different biochar samples by X-ray fluorescence and Fourier transform infrared spectroscopy revealed a nutrient-rich composition with carbon, calcium, and potassium contents that ranged from 35 to 48%, from 1.6 to 24%, and from 1.5 to 28.5%, respectively. In phytotoxicity tests, the highest germination rate (45%) was observed with Coffee residue biochar obtained at 300°C (application rate of 1%) and the longest shoot length (25cm) with orange peel biochar obtained at 300°C (application rate of 1%). Germination rate and shoot length were not significantly different between biochar-exposed soils and control soils (without biochar), indicating no toxic effect due to biochar addition. Washing biochar improved germination rates significantly (control: 98%; potato peel biochar: 92%; banana peel biochar: 83%). The longest shoot length (8.3cm) was obtained with the washed potato peel biochar (pyrolysis temperature = 400°C) extract. These findings suggest that biochar can be safely used as a soil amendment without harming the environment or hindering plant growth. The Tukey honestly significant difference (HSD) test results further emphasized the influence of different factors, such as pyrolysis temperature and feedstock type, in biochar applications.

Phytotoxicity Assessment of Agro-Industrial Waste and Its Biochar: Germination Bioassay in Four Horticultural Species

This study investigated the phytotoxicity of agro-industrial wastes (almond, walnut, pistachio and peanut shells, asparagus spears, and brewer’s spent grain) and their biochar through germination bioassays in several horticultural species: green pea, lettuce, radish, and arugula. Biowaste was pyrolyzed under controlled conditions to produce biochar, and both biowaste and biochar were characterized. Germination bioassay was conducted using seeds exposed to different dilutions of aqueous extract of biowaste and their biochar (0, 50, and 100%). Germination percentage, seed vigor, germination index, and root and aerial lengths were evaluated. The results showed that the phytotoxicity of the biowaste was significantly different to that of its biochar. The biochar obtained demonstrated changing effects on germination and seedling growth. In particular, biochar extracts from spent brewers grains, walnut shells, and pistachio shells showed 5–14% increases in seed vigor and root and aerial length. Furthermore, the response of different species to both agro-industrial waste and biochar revealed species-specific sensitivity. Seeds of lettuce and arugula species were more sensitive to aqueous extracts than radish and green peas. This knowledge not only elucidates the behavior of agro-industrial waste-based biochar in the early stage of plant development but also provides valuable insights regarding phytotoxicity, seed sensitivity, and the variables involved in germination.

Identifying Quinones in Complex Aqueous Environmental Media (Biochar Extracts) through Tagging with Cysteine and Cysteine-Contained Peptides and High Resolution Mass Spectrometry Analysis.

Quinones are among the most important components in natural organic matter (NOM) for redox reactions; however, no quinones in complex environmental media have been identified. To aid the identification of quinone-containing molecules in ultracomplex environmental samples, we developed a chemical tagging method that makes use of a Michael addition reaction between quinones and thiols (-SH) in cysteine (Cys) and cysteine-contained peptides (CCP). After the tagging, candidates of quinones in representative aqueous environmental samples (water extractions of biochar) were identified through high-resolution mass spectrometry (HRMS) analysis. The MS and UV spectra analysis showed rapid reactions between Cys/CCP and model quinones with β-carbon from the same benzene ring available for Michael addition. The tagging efficiency was not influenced by other co-occurring nonquinone representative compounds, including caffeic acid, cinnamic acid, and coumaric acid. Cys and CCP were used to tag quinones in water extractions of biochars, and possible candidates of quinones (20 and 53 based on tagging with Cys and CCP, respectively) were identified based on the HRMS features for products of reactions with Cys/CCP. This study has successfully demonstrated that such a Michael addition reaction can be used to tag quinones in complex environmental media and potentially determine their identities. The method will enable an in-depth understanding of the redox chemistry of NOM and its critical chemical compositions and structures.

Comparative investigation of powder and extract of biochar from Broussonetia papyrifera on the growth and eco-physiological attributes of Vigna radiata

This study compared the impact of biochar (in powder and extract forms) derived from the invasive tree Broussonetia papyrifera on the growth and eco-physiological responses of Vigna radiata (mung bean) under laboratory and experimental dome environments. The primary objective was to investigate the sustainable utilization potential of biochar derived from invasive plants. Powdered biochar was mixed into garden soil at amendment rates of 0.5%, 1%, 2%, and 4%, while for extract treatments, the seedlings were irrigated with extracts of these concentrations. The responses of plants were found to be dependent on the concentration and type of treatment (i.e., powder or extract) used. The highest levels of growth and eco-physiological responses were observed at a concentration of 1% for biochar extract and 2% for powdered biochar. In addition, the impacts were more pronounced in the roots than in the shoots. The biochar amendment resulted in a 7‒73% increase in root length and a 12‒148% increase in plant dry biomass when compared to the control. Crop growth, water use efficiency, and leaf area were greater in powdered biochar, but net photosynthesis (Pn), transpiration rate, and stomatal conductance were higher in plants treated with biochar extract. Adding powdered biochar to soil increases its pH, electrical conductivity (EC), moisture content, soil organic C, and amounts of available N, P, and K; however, the effects of applying biochar extracts were less pronounced. Crop growth and eco-physiological responses were found to be positively correlated, regardless of the biochar form used. Following biochar extract treatment, EC was found to be negatively correlated with Pn. The study revealed that powdered biochar had superior growth responses and soil improvement compared to biochar extract at higher concentrations. However, biochar extract also had comparable effects and can be beneficial in short-term cropping systems such as urban farming (e.g., in kitchen gardens and vegetable production) at lower concentrations (up to 2%). The findings of the study provide a baseline for future evaluations regarding the sustainable application of biochar liquor (water extract) as a source of nutrients and the powdered residual biochar as a potential material for adsorbing environmental contaminants or improving soil quality.

Aqueous extract of coconut shell biochar as a pre-germination treatment increases seed germination and early seedling growth in chiltepín pepper (Capsicum annuum var. glabriusculum)

Since the fruit of the Capsicum annuum L. var. glabriusculum (Dunal) Heiser and Pickergil (chiltepín pepper) has a low germination rate, we sought to determine whether using an aqueous biochar extract could improve this. Germination tests were performed out in Petri dishes, using wild chiltepín pepper seeds collected in Sonora, México, which were exposed for 24 h to aqueous extracts of coconut shell biochar (CSBA) at different doses (0.05, 0.10, 0.25, 0.50, 0.75, and 1.00%, w/v) and a control comprising deionized water. In addition to quantifying the germination rate, we determined the physical quality, viability, imbibition, electrical conductivity, seed pH, and capsaicin content. The fast green test showed an ideal physical quality (p = 0.5475), an imbibition rate > 65% (p > 0.05), and high viability 98.4% (p > 0.05). The wild chiltepín pepper seeds exposed to the CSBA0.05 and CSBA0.25 treatments increased the percentage germination rate (p < 0.001) to 80.9% and 71.7%, respectively. A higher percentage of normal seedlings resulted from CSBA0.05, CSBA0.10 and CSBA1.00 (p < 0.01), and a greater shoot length was obtained with CSBA0.05 (p < 0.01). The exposure of wild chiltepín seeds to aqueous CSBA for 24 h at low doses (CSBA0.05 and CSBA0.25) increase the germination rate, while CSBA0.05 could enhance early seedling growth.

Biochar extract compounds alter germination and growth of crop seed

Positive or negative plant growth effects due to soluble organic biochar compounds are not well understood. Increasing quantities (0 g, 0.5 g, 2.5 g, and 5 g) of four different biochars were extracted with 0.1 M HCl, which were separated and marked as W, X, Y, and Z. Corn and rice seeds were treated with biochar extract solution. The rice straw Y and Z solutions positively affected corn germination, while the cotton straw Z solution negatively affected it. When differences were present, the biochar extract solutions always caused reduction in rice seed germination. The rice straw and cotton straw solutions tended to increase, the wheat straw Y and Z solutions tended to decrease, while little differences were evident in terms of the effects of the Spartina alterniflora solution on corn bud and root length when compared to the control. Increasing the biochar solution extract treatments reduced the rice bud and root length when compared to the control, especially with solution Z. Organic compounds, e.g., triethyl phosphate, 2,4-bisphenol, were present in the solutions, which likely promoted seed growth at lower concentrations. Determining the presence of biochar organic moieties helped with designing biochars for enhanced seed germination, growth, and crop productivity.

Exploring the negative effects of biochars on the germination, growth, and antioxidant system of rice and corn

This study investigated the effects of biochars pyrolyzed at different temperatures on plant germination and growth and attempted to determine the mechanisms underlying those effects. The experimental results showed that phytotoxicity of biochar pyrolyzed at 500 or 800 °C was significantly higher than that of biochar pyrolyzed at 200 °C, especially at high dosages (200.0 and 300.0 g/L). However, concentrations of heavy metals and polycyclic aromatic hydrocarbon (PAHs) in biochar pyrolyzed at 500 and 800 °C were lower than those in biochar pyrolyzed at 200 °C. The inhibitory effect of aqueous biochar extract on seed germination was significantly weaker than that of biochar. Electron paramagnetic resonance (EPR) signal intensity was enhanced with increasing pyrolysis temperature, which indicates the existence of a greater number of free radicals. Furthermore, •OH and •O2− were the primary reactive oxygen species in the biochar system. It can be concluded that the phytotoxicity of biochar pyrolyzed at high temperatures (>500 °C) enables to attributing free radical-induced oxidative damage, whereas that of biochar produced at low temperatures (200 °C) results in the presence of conventional contaminants (such as heavy metals and PAHs). The information obtained in this study provides a more comprehensive understanding of the potential risk of free radicals in plant system biochar.

Expanding the Analytical Window for Biochar Speciation: Molecular Comparison of Solvent Extraction and Water-Soluble Fractions of Biochar by FT-ICR Mass Spectrometry.

Biochar, a low-density yet carbon-rich material derived from different organic materials pyrolyzed under low or no oxygen conditions, has been widely studied as a soil amendment, for greenhouse gas mitigation and in remediation of trace element-contaminated soils. Molecular speciation of biochar compounds has been challenging due to low solubility, aggregation, and immense compositional polydispersity that challenges nearly all mass spectrometry methods routinely applied to carbon-based organic materials. Through a combined technique approach that applies advanced analytical strategies, we provide bulk and molecular characterization of Kentucky bluegrass biochar that can be applied to any biomass or biochar sample. First, we characterize Kentucky bluegrass biochar chemical functional groups by solid-state magic-angle spinning dynamic nuclear polarization NMR (MAS-DNP NMR) and resolve aromatic and aliphatic signals from the pyrogenic material and intact plant material. Next, we isolate water-soluble biochar species by solid-phase extraction followed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and identify highly polar, oxygen species across a wide carbon number range. Solvent fractionation of biochar further expands the compositional range and identifies condensed polycyclic aromatic species across nonpolar and polar classes detected by two ionization modes (-ESI and +APPI) by FT-ICR MS. Plotting biochar species with DBE versus carbon number highlights the pericondensed molecular structural motif that persists across numerous heteroatom classes and ionization modes. To the best of our knowledge, this is the first molecular level identification of nonfunctionalized PAHs in biochar extracts by APPI FT-ICR MS. Thus, we identify biochar species that span the same compositional space as coal, heavy oil asphaltenes, and coal tar and correspond to condensed ring PAHs.

Preparation, characterization and agri applications of biochar produced by pyrolysis of sewage sludge at different temperatures

Sewage sludge (SS) is an abundantly available feedstock, which is generally considered as potential threat to human health and environment. Its utilization in any process would be of great help for environmental sustainability. Accordingly, this work aimed to prepare and characterize the sewage sludge biochar (SSB) at temperatures, i.e. (500, 450, 400, and 350 °C), and further analyze the available nutrients and contaminants as well as agri application potential. The results indicated that the total nitrogen (TN), electrical conductivity (EC), and total organic carbon (TOC) content in SSBs decreased with increasing pyrolysis temperature. The overall concentration of polycyclic aromatic hydrocarbons (PAHs) in SSBs was substantially lower (1.8–9.7-fold depending on pyrolysis temperature) than in SS. Pyrolysis of SS enriched the heavy metals content in SSBs and the relative enrichment factor (RE) factor varied between 1.1 and 2.1 depending on the pyrolysis temperature. Furthermore, compared to SS, the leaching rate of heavy metals was significantly decreased in SSBs (1.1–100-fold depending on the pyrolysis temperature) and the pyrolysis temperature of 400–450 °C prevented the Ni, Pb, Cr, and Zn leaching in SSB. The total PAH and heavy metals content in biochars were below the control standard for land application. Finally, testing of the growth-promoting effect of biochar extracts on fenugreek plants revealed that SSB prepared at 350 °C significantly stimulated the root and shoot length of 5-days old seedlings. This study provides important data for potential environmental risks of SSB applications.

Rice Seedling Growth Promotion by Biochar Varies With Genotypes and Application Dosages.

While biochar use in agriculture is widely advocated, how the effect of biochar on plant growth varies with biochar forms and crop genotypes is poorly addressed. The role of dissolvable organic matter (DOM) in plant growth has been increasingly addressed for crop production with biochar. In this study, a hydroponic culture of rice seedling growth of two cultivars was treated with bulk mass (DOM-containing), water extract (DOM only), and extracted residue (DOM-free) of maize residue biochar, at a volumetric dosage of 0.01, 0.05, and 0.1%, respectively. On seedling root growth of the two cultivars, bulk biochar exerted a generally negative effect, while the biochar extract had a consistently positive effect across the application dosages. Differently, the extracted biochar showed a contrasting effect between genotypes. In another hydroponic culture with Wuyunjing 7 treated with biochar extract at sequential dosages, seedling growth was promoted by 95% at 0.01% dosage but by 26% at 0.1% dosage, explained with the great promotion of secondary roots rather than of primary roots. Such effects were likely explained by low molecular weight organic acids and nanoparticles contained in the biochar DOM. This study highlights the importance of biochar DOM and crop genotype when evaluating the effect of biochar on plants. The use of low dosage of biochar DOM could help farmers to adopt biochar technology as a solution for agricultural sustainability.

Fertilizing behavior of extract of organomineral-activated biochar: low-dose foliar application for promoting lettuce growth

BackgroundFostering plant growth and improving agricultural yields by adding “macro”-sized biochar to soil has been extensively explored. However, the impact and mechanism of action of aqueous extracts of biochar applied as foliar fertilizer on plant growth and physiology is poorly understood, and was the objective of this study. Extracts were produced from biochars derived from pine wood:clay:sand (PCS-BC; 70:15:15) and wheat straw:bird manure (WB-BC; 50:50) and tested at two dilutions each. The plant influence of the biochar extracts and dilutions were compared with chemical fertilizer made up to the same minor trace element compositions as the applied extracts and a control treatment consisting of only deionized water.ResultsThe WB-BC extract was more alkaline than the PCS-BC extract and exhibited higher electrical conductivity values. Similar to the biochars from which they were derived, the WB-BC extract had higher concentrations of dissolved mineral elements and organic matter than the PCS-BC extract. Despite major differences in chemical composition between the PCS-BC and WB-BC extracts, there was virtually no difference in plant performance between them at any chosen dilution. Foliar application of PCS25, WB50, and WB100 led to a significant increase in the plant fresh biomass in comparison to their corresponding chemical fertilizer and to deionized water. Plant growth parameters including number of leaves and chlorophyll contents in plants treated with biochar extract foliar sprays were significantly higher than in all the other treatments. Electron microscopy and spectroscopy studies showed the deposition of macro- and nanoscale organomineral particles and agglomerates on leaf surfaces of the examined PCS25-treated plant. Detailed study suggests that carbon nanomaterials and TiO2 or Si-rich nanoscale organomineral complexes or aluminosilicate compounds from biochar extract were main contributors to increased plant growth and improved plant performance.ConclusionThese results suggest that biochar extracts have the potential to be used as nanofertilizer foliar sprays for enhancing plant growth and yield.

Biochar’s Leacheates Affect the Abscisic Acid Pathway in Rice Seedlings Under Low Temperature

Organic molecules of biochar’s leacheates are known to increase the cold resistance of rice seedlings. Yet, it remains unclear whether the organic molecules of biochar leacheates can interact with the abscisic acid (ABA) signaling pathway associated with low temperature. This study used experiments and bioinformatics (molecular docking) to determine which of the organic molecules of biochar’s leacheates could influence the ABA signaling pathway. Specifically, we investigated whether these molecules affected ABA, a plant hormone linked to cold resistance. The contents of endogenous ABA and its precursor carotenoids were determined under low-temperature stress (10°C) and treatment with different concentrations of biochar leacheates. With increased leacheate concentrations, the endogenous ABA and carotenoid contents also increased, as did the expression of ABA- and cold-related genes. When rice seedlings were instead treated with exogenous ABA, it also affected the above-measured indexes; hence, we surmised that certain water-soluble organic molecules of biochar could exert a similar effect as ABA. We first used gas chromatography/mass spectrometry (GC/MS) to identify the organic molecules in the biochar extract, and then we used molecular docking software Autodock to show how they interact. We found that the molecule (1R, 2R, 4S)-2-(6-chloropyridin-3-yl)-7-azabicyclo(2.2.1)heptane was simplified, as Cyah could dock with the ABA receptor protein OsPYL2 in rice, which shows Cyah in biochar is probably an analog of ABA, with a similar function. Based on these results, we conclude that organic molecules of biochar’s leacheates could enter into rice plants and interact with ABA-related proteins to affect the ABA signaling pathway, thereby improving the cold stress resistance of plants.

Production of a biofertilizer from exhausted grape marc waste: agronomic and environmental impact on plant growth

Biochars produced from exhausted grape marc waste were considered a potential source for agriculture biofertilization. Results indicated that the biochar application did not show a significant effect on ryegrass fresh weight increase. The pyrolysis temperature influenced the fresh and dry matter yield since it interferes with phosphorus bioavailability for plant growth. Potassium intakes were positively affected but not statistically significant. The % of soil stable aggregates decreased after 60 days. In the short term, there is no significant effect on soil structural stability. Biochar incorporation led to domination of large macro-aggregates, which are instables compared with small macro-aggregates. A dose of 15 t ha−1 considerably reduced the leached soil and thus improved water retention by changing soil porosity. Soil pH and electric conductivity markedly increased for all treatments after 60 days of incubation. Biochar extract had a significant inhibitory effect on Fusarium oxysporum and Phytophthora sp. The use of exhausted grape marc waste to produce a biochar has shown a good potential for carbon and water sequestration in soil.

The Water-Soluble Pool in Biochar Dominates Maize Plant Growth Promotion Under Biochar Amendment

Although amending biochar into agricultural soils has been regarded as an effective measure to improve crop productivity, it remains unclear why biochar increases crop yield. The objective of this study was to compare the relative contribution of different biochar components in crop growth promotion. Three biochar components were separated: (i) water-soluble biochar extract (BE), (ii) mineral nutrients from biochar ash (BA), and (iii) washed biochar residue (WB). Two soils (Anthrosol and Primosol) with distinctly different organic carbon content, soil texture and land use were amended with the three biochar components and their effects on maize (Zea mays L.) growth were tested in a pot experiment. We hypothesized that (1) plant grown in the Anthrosol benefitted more from the water-soluble compounds of biochar than from its mineral nutrients or washed residue, since the soil is already fertile and has a good structure; (2) plant grown in the Primosol benefitted more from the mineral nutrients of biochar and its washed residual, since the soil is nutrient-poor and has a poor structure. The addition of biochar and its three components increased maize aboveground biomass for both soils. In the Anthrosol, BE, BA, and WB increased the aboveground biomass by 41.6%, 32.7%, and 27.1%; in the Primosol, they increased the aboveground biomass by 41.3%, 24.4%, and 18.2%, respectively. BE had the highest plant growth-promoting effect compared to the other two biochar components, which was regardless of soil condition. In addition, the biomass, total volume, surface area, and number of maize root tips under BE amendment were significantly enhanced, particularly the fine roots (< 0.2 mm in diameter). And a strong positive correlation was observed between maize aboveground biomass and the total length of the fine roots. The results demonstrated that the water-soluble compounds present in biochar, in addition to the mineral nutrients and the washed biochar residue, dominate the plant growth promotion under both soil conditions.

Biochar-mediated enhanced ethanol fermentation (BMEEF) in Zymomonas mobilis under furfural and acetic acid stress

BackgroundPretreatment of lignocellulosic biomass generates different types of inhibitors (e.g., furfural and acetic acid), which could remarkably inhibit subsequent ethanol fermentation. Here, biochar as an additive in the fermentation broth was first applied to enhance ethanol production by Z. mobilis wild-type strain ZM4 in the presence of typical inhibitors.ResultsThis study showed that the biochar-mediated tolerance to furfural and acetic acid for the strain Z. mobilis ZM4 was the highest reported level, resulting in much higher ethanol productivity under stress conditions than that in non-treated conditions. Further analysis showed that adsorptive detoxification was not the controlling factor for enhanced ethanol production under stress conditions, attributed to its low removal of furfural (< 20%) and incapability of acetic acid removal. When biochar was filtered from the biochar-treated inhibitor-containing broth, it still showed enhanced ethanol production. Furthermore, Z. mobilis immobilized on biochar was also observed. Thus, biochar extracts in the fermentation broth and cell immobilization on biochar might be the controlling factors for enhanced ethanol production under stress conditions.ConclusionsThese results indicate that biochar-mediated enhanced ethanol fermentation (BMEEF) might be a promising strategy for ethanol production from lignocellulosic biomass.

Phytoremediation of heavy metals under an oil crop rotation and treatment of biochar from contaminated biomass for safe use

The disposal of contaminated plants limits the use of phytoremediation. Therefore, the disposal of contaminated sunflower was investigated after determining the phytoremediation of heavy metals under an oil crop rotation of sunflower (Helianthus annuus L)–sesame (Sesamum indicum L.). In the field experiment, the extraction efficiency of sunflower-sesame rotation was 0.07% for lead (Pb); 1.37% for zinc (Zn); 1.10% for copper (Cu); and 6.12% for cadmium (Cd). Contaminated sunflower stems were pyrolyzed at different temperature. The biochar produced at 300 °C was extracted in a two-step process (acid-extraction from biochar and metals precipitation in alkaline condition). At pH = 1, 65.67% of the Cd and much potassium (K) were extracted. After acid-extraction, adjust the pH of filtrate to 10, metals were precipitated and then separated from the K-enriched solution. Therefore, pyrolysis can process contaminated residues, and the biochar extracts can be reutilized as fertilizer to off-site crop production. Thus, an oil crop-rotation system, in addition to creating economic benefits, can be used by local farmers in contaminated soils.

Improving pea quality with vermicompost tea and aqueous biochar: Prospects for sustainable farming in Southern Africa

One of the main factors responsible for successful sustainable food production is vigorous seedling establishment. The role of organic extracts (vermicompost tea and aqueous biochar) on improving seed performance has not been fully explored in South Africa. Pea seed germination and emergence experiments using different concentrations of organic extracts were conducted according to International Seed Testing Association (ISTA) rules, and arranged in completely randomised block designs with four replications. Vermicompost tea (VC) significantly improved seed germination and emergence percentages, speed of germination and emergence, and physiological processes compared with biochar (BC) and vermicompost tea with microbial supplements (augmented). In contrast, biochar improved seedling growth by 39% compared to vermicompost tea. Application of the BC and VC extracts led to a 12% and 18% increase in pea germination percentages respectively. Similarly, BC and VC extracts at 10% concentration were effective in yielding optimal photosynthetic responses. The 5% and 10% VC, or 2.5% BC extracts are recommended for improving speed of germination, optimal germination and emergence percentages of pea seeds. Application of these extracts will be beneficial for resource-poor farmers in marginal lands, since these organic extracts are cheaper, easier to produce and more environmental friendly than the available commercial fertilisers. This study has shown that vermicompost tea provides essential nutrients for pea seed establishment, thus negating the need to use chemical fertilisers for effective seedling establishment.

Biochar DOM for plant promotion but not residual biochar for metal immobilization depended on pyrolysis temperature

While biochar on metal immobilization was well understood, a small pool of dissolvable organic matter (DOM) from biochar was recently recognized as a bioactive agent for plant growth promotion. However, how the molecular composition and plant effects of this fraction and the performance for metal immobilization of the DOM-removed biochar could vary with pyrolysis temperature had been not well addressed. In this study, wheat straw biochar pyrolyzed at a temperature of 350 °C, 450 °C, 550 °C were extracted with hot water to separate the DOM fraction. The obtained biochar extracts (BE350, BE450, and BE550) were tested as foliar amendment to Chinese cabbage while the extracted (DOM-removed) biochars were tested for heavy metal immobilization in a contaminated soil. The results showed that BE350 was higher in organic matter content, abundance of organic molecules and mineral nutrients than BE450 and BE550. Compared to control, foliar application of BE350 significantly enhanced the shoot biomass (by 89%), increased leaf soluble sugar content (by 83%) but reduced leaf content of nitrate (by 34%) and of potential toxic metals (by 49% for Cd and by 30% for Pb). Moreover, BE350 treatment increased gene expression of nitrate reductase and glutamine synthetase enzyme activity of the tested plant. Meanwhile, soil amendment of DOM-extracted biochars significantly decreased soil CaCl2 extractable pool of Cd, Pb, Cu and Zn in a range of 27%–78%. Thus, the performance of DOM extract of biochar on plant growth promotion was indeed dependent of pyrolysis temperature, being greater at 350 °C than at higher temperatures. In contrast, metal immobilizing capacity of biochar was regardless of pyrolysis temperature and DOM removal. Therefore, pyrolyzing wheat straw at low temperature could produce a biochar for valorized separation of a significant DOM pool for use in vegetable production, leaving the residual biochar for amendment to metal contaminated soil.

Influence of temperature and duration of pyrolysis on the property heterogeneity of rice straw biochar and optimization of pyrolysis conditions for its application in soils

The study reports an investigation into the effects of temperature and duration of the pyrolysis on the yield and properties of the rice straw biochar and their optimization for application in soil based on the results of seed germination test. As a continuation, the effects of rice straw biochar on the growth of mung beans germinated using extracts of biochar, which were maintained at different pHs was studied. Biochar solvent extraction was done by mixing a predetermined dose of rice straw biochar to solutions initially maintained at five different pH conditions (4, 6, 7, 8, and 10). The biochar extracts were also characterized for their pH, electrical conductivity, and nutrient values and correlated with the germinated seed lengths. Further, this study based on the results of seed germination optimized the rice straw biochar production conditions with such properties to promote maximum seedling growth. Results showed that the yield of biochar decreased from 45.04% to 33.45% as temperature raised from 400 °C to 700 °C. The properties of biochar are primarily affected by the temperature as compared to the heating duration of the pyrolysis. The crystallinity index in the rice straw biochar decreased by 15.25% with the increase in the temperature from 400 °C to 700 °C. Correlation test among seed lengths and biochar extracts properties showed that the seed growth was directly correlated with the increase in the nutrient values at all pH conditions. Based on the germination test, the optimized conditions for the maximum seedling growth observed as for high nutrients, carbon (35–40%) and moderate nitrogen (3–4%), ash (32–35%), yield (35–40%) and cation exchange capacity (40–45 cmol/kg), carbon-nitrogen ratio (22–25:1), low oxygen-carbon ratio (0.7–0.8), ideal pH (8–9), and low volatiles (44–48%). The optimized pyrolytic temperature and duration to produce rice straw biochar with above-listed properties modelled as 500–600 °C and 80–100 min respectively.

Pyrolysis of contaminated wheat straw to stabilize toxic metals in biochar but recycle the extract for agricultural use

Minimizing potential environmental risks of toxic metals is a prerequisite for recycling crop straw from contaminated farmlands. In this study, feedstocks of wheat straw were collected from paddy fields with low and high level of metal contamination and pyrolysed at temperature of 350 °C and of 550 °C, respectively. The produced biochars were subsequently extracted with hot water and potassium hydroxide solution. Contents of potentially toxic metals (PTEs), polycyclic aromatic hydrocarbons (PAHs) and mineral nutrients were analyzed both of the biochars and their extracts. To test the effect of the biochar extracts on plant growth and quality, a pot experiment was carried out with foliar amendment to Chinese cabbage. The results showed that contents of nutrients, PTEs and PAHs of both the biochars and their extracts differed significantly both between feedstocks and between pyrolysis temperatures. Total concentrations of PTEs and PAHs of the biochars were well under the recommended quality limits with their negligible presence in the biochar extracts. The pot experiment revealed a very significant promotion for cabbage yield and quality by the extracts of biochar pyrolysed at 350 °C, regardless of the feedstock. Thus, pyrolysing crop straw from metal contaminated fields at 350 °C could be an option to stabilize toxic metals in biochar as soil amendment but to recycle the biochar extract as foliar fertilizer to off-site crop production. Therefore, a viable mechanism is urged to develop in China where direct crop residue return has been state-funded under a policy of strict ban of straw burning.