Potential of miscanthus biochar to improve sandy soil health, in situ nickel immobilization in soil and nutritional quality of spinach

Nickel (Ni) phytotoxicity and detoxification mechanisms: A review

Scientists studying the environment, physiology, and biology have been particularly interested in nickel (Ni) because of its dual effects (essentiality and toxicity) on terrestrial biota. It has been reported in some studies that without an adequate supply of Ni, plants are unable to finish their life cycle. The safest Ni limit for plants is 1.5 μg g^-1, while the limit for soil is between 75 and 150 μg g^-1. Ni at lethal levels harms plants by interfering with a variety of physiological functions, including enzyme activity, root development, photosynthesis, and mineral uptake. This review focuses on the occurrence and phytotoxicity of Ni with respect to growth, physiological and biochemical aspects. It also delves into advanced Ni detoxification mechanisms such as cellular modifications, organic acids, and chelation of Ni by plant roots, and emphasizes the role of genes involved in Ni detoxification. The discussion has been carried out on the current state of using soil amendments and plant-microbe interactions to successfully remediate Ni from contaminated sites. This review has identified potential drawbacks and difficulties of various strategies for Ni remediation, discussed the importance of these findings for environmental authorities and decision-makers, and concluded by noting the sustainability concerns and future research needs regarding Ni remediation.

Investigating the role of bentonite clay with different soil amendments to minimize the bioaccumulation of heavy metals in Solanum melongena L. under the irrigation of tannery wastewater

Wastewater from tanneries is a major source of heavy metals in soil and plants when used for crop irrigation. The unavoidable toxicological effects of this contamination, however, can be minimized through two independent steps discussed in the present study. In the first step, a batch sorption experiment was conducted in which Cr was adsorbed through bentonite clay. For this purpose, DTPA extraction method was used to analyze Cr concentration in the soil after regular time intervals (0.5, 1, 2, 6, 8, 9, 10.5, 11.5, and 20.3 h) which reduced Cr concentration from 38.542 mgL^-1 for 30 min to 5.6597 mgL^-1 for 20.3 h, respectively, by applying 1% bentonite. An increase in the contact time efficiently allowed soil adsorbent to adsorb maximum Cr from soil samples. In the second step, a pot experiment was conducted with 10 different treatments to improve the physiological and biochemical parameters of the Solanum melongena L. irrigated under tanneries' wastewater stress. There were four replicates, and the crop was harvested after 30 days of germination. It was seen that the application of wastewater significantly (P < 0.01) reduced growth of Solanum melongena L. by reducing root (77%) and shoot (63%) fresh weight when compared with CFOP (Ce-doped Fe₂O₃ nanoparticles); chlorophyll a and b (fourfolds) were improved under CFOP application relative to control (CN). However, the deleterious effects of Cr (86%) and Pb (90%) were significantly decreased in shoot through CFOP application relative to CN. Moreover, oxidative damage induced by the tannery's wastewater stress (P < 0.01) was tolerated by applying different soil amendments. However, results were well pronounced with the application of CFOP which competitively decreased the concentrations of MDA (95%), H₂O₂ (89%), and CMP (85%) by efficiently triggering the activities of antioxidant defense mechanisms such as APX (threefold), CAT (twofold), and phenolics (75%) in stem relative to CN. Consequently, all the applied amendments (BN, BT, FOP, and CFOP) have shown the ability to efficiently tolerate the tannery's wastewater stress; results were more pronounced with the addition of CFOP and FOP+BT by improving physiological and biochemical parameters of Solanum melongena L. in an eco-friendly way.

Iron-Doped Biochar Regulated Soil Nickel Adsorption, Wheat Growth, Its Physiology and Elemental Concentration under Contrasting Abiotic Stresses

The prevalence of abiotic stresses hampers soil health and plant growth in most ecosystems. In this study, rice husk iron-enriched biochar (BC) was prepared and its superiority in terms of nutrients enrichment, porosity and different acidic functional group (O-H, C=O) relative to simple biochar was confirmed through scanning electron microscopic, X-ray fluorescence and Fourier transform infrared analysis. To further evaluate its nickel (Ni), salt (NaCl) and carbonate (CaCO3) stress mitigating impact on wheat physiology and biochemical attributes, a pot experiment was conducted using; BC (1%), Ni (0.5 mM NiNO3), Na (100 mM NaCl) and CO3 (100 mM CaCO3) and with twelve treatments; T1; Control, T2; NiNO3, T3; CaCO3, T4; NaCl, T5; BC, T6; Ni + BC, T7; CaCO3 + BC, T8; NaCl + BC, T9; Ni + CaCO3 + BC, T10; Ni + NaCl + BC, T11; CaCO3 + NaCl + BC, T12; Ni + NaCl + CaCO3 + BC. The Langmuir isotherm model revealed the maximum Ni adsorption capacity (2433 mg g−1) in treatments where Ni was applied with BC soil. Maximum soil DTPA-extractable Ni was found in the T9 treatment; however, Ni concentration was not reported in wheat roots while only trace amounts of Ni were found in wheat shoots with the T9 treatment. It was suggested that BC has the capacity to induce the immunization effect in plant roots by providing additional Fe so their ionic homeostasis and redox metabolism worked properly. This argument was further paved by the enhanced adsorption of these toxic ions in the presence of BC-favored wheat growth as indicated by maximum increases in shoot iron and potassium concentrations under Ni + CaCO3 + BC, relative to control. Furthermore, the decrease in shoot hydrogen peroxide (H2O2) (20%) and malondialdehyde (32%) concentrations and increase in shoot ascorbate peroxidase (81%) and catalase (three-fold) activities under Ni + BC relative to Ni + NaCl + CaCO3 + BC controlled the cell membrane damage. In conclusion, BC proved to be an excellent amendment to reduce the toxic effects of Ni, NaCl and CaCO3 stresses and enhance wheat growth and nutrition.

A review of pristine and modified biochar immobilizing typical heavy metals in soil: Applications and challenges

In recent years, the application of biochar in the remediation of heavy metals (HMs) contaminated soil has received tremendous attention globally. We reviewed the latest research on the immobilization of soil HMs by biochar almost in the last 5 years (until 2021). The methods, effects and mechanisms of biochar and modified biochar on the immobilization of typical HMs in soil have been systematically summarized. In general, the HMs contaminating the soil can be categorized into two groups, the oxy-anionic HMs (As and Cr) and the cationic HMs (Pb, Cd, etc.). Reduction and precipitation of oxy-anionic HMs by biochar/modified biochar are the dominant mechanism for reducing HMs toxicity. Pristine biochar can effectively immobilize cationic HMs. The commonly applied modification method is to add substances that can precipitate HMs to the biochar. In addition, we assessed the risks of biochar applications. For instance, biochar may cause the leaching of certain HMs; biochar aging; co-transportation of biochar nanoparticles with HMs. Future work should focus on the artificial/intelligent design of biochar to make it suitable for remediation of multiple HMs contaminated soil.

Effect of the Co-Application of Eucalyptus Wood Biochar and Chemical Fertilizer for the Remediation of Multimetal (Cr, Zn, Ni, and Co) Contaminated Soil

Contamination of soil with heavy metals is a worldwide problem, which causes heavy metals to release into the environment. Remediation of such contaminated soil is essential to protect the environment. The aims of this study are: first, to compare the effect of biochar and the joint application of biochar with fertilizer for the phytoremediation of heavy metals-contaminated soil using Acacia auriculiformis; second, to study the effect of the application rate of biochar in improving the physicochemical properties of the soil. The soil samples were collected from an active coal mine dump and assessed for their physicochemical properties and heavy metals toxicity. Initial results indicated that the soil has poor physicochemical properties and was contaminated with the presence of heavy metals such as Zn, Ni, Cu, Cr, and Co. Later, the heavy metals-contaminated soil was mixed with the 400 and 600 °C biochar, as well as the respective biochar–fertilizer combination in varying mixing ratios from 0.5 to 5% (w/w) and subjected to a pot-culture study. The results showed that the application of both varieties of biochar in combination with fertilizer substantially improved the physicochemical properties and reduced the heavy metals toxicity in the soil. The biochar and fertilizer joint application also substantially improved the soil physiochemical properties by increasing the application rate of both varieties of biochar from 0.5 to 5%. The soil fertility index (SFI) of the biochar and biochar–fertilizer amended soil increased by 49.46 and 52.22%, respectively. The plant’s physiological analysis results indicated a substantial increase in the plant’s shoot and root biomass through the application of biochar and biochar–fertilizer compared to the control. On the other hand, it significantly reduced the heavy metals accumulation and, hence, the secretion of proline and glutathione hormones in the plant cells. Therefore, it can be concluded that the joint application of biochar with the application rate varying between 2.5 to 5% (w/w) with the fertilizer significantly improved the physicochemical properties of the soil and reduced the heavy metals toxicity compared to the controlled study.

Reducing cadmium bioaccumulation in Theobroma cacao using biochar: basis for scaling-up to field

The intake of Cd-enriched food is the main Cd pathway for the nonsmoking population. In some cases, Cd bioaccumulates in edible plant parts which comprise risk to consumers, because of Cd is a harmful heavy metal that can cause potent environmental and health hazards. For instance, Cd enrichment of cacao seeds have led to Cd enrichment of cacao-based products. In Latin America and the Caribbean, Cd bioaccumulation in cacao seeds occurs in different regions with diverse edaphoclimatic conditions, which makes it difficult to select soil remediation alternatives. Limited resources require that potential amendments must be carefully investigated through laboratory and/or greenhouse conditions before scaling up to field experiments. In this study, we evaluated the effectiveness of four biochars: coffee-, quinoa-, and inoculated- and palm-biochar, derived from three feedstocks: coffee husk, quinoa straw, and oil palm residues, respectively. Biochars were applied in two rates (1 and 2% w/w) in two soils, one moderately acidic and one slightly alkaline (Cd-spiked and non-spiked). CCN-51 cacao plants were used for the greenhouse experiment. After 130 days, biometric parameters, the bioavailability of Cd in the soil, and the concentration of Cd and mineral nutrients in the plants were measured. Quinoa biochar at the 2% significantly decreased (P < 0.01), by ∼71%, bioavailable Cd in moderately acidic and slightly alkaline soils, and leaf-Cd by ∼48%. Soil pH, electrical conductivity, and effective cation exchange capacity were significantly (P < 0.01) correlated with bioavailable soil and leaf-Cd. Biochar characteristics, such as ash contents, basic cations content, and surface functional groups could be used as indicators for the selection of biochars to reduce Cd uptake by cacao. Additionally, application of quinoa derived biochar provided P and K, which could increase productivity to offset mitigation costs. Overall, incorporation of quinoa biochar at 2% rate is effective for lowering bioavailable Cd in different soil types which reduces leaf-Cd in cacao plants.

•

Biochar ash content helps to increase soil pH and reduce Cd bioavailability.

•

Quinoa biochar at 2% reduced up to 80% bioavailable Cd in moderately acidic and slightly alkaline soils.

•

Quinoa biochar at 2% lowered, up to 48%, Cd concentration in cacao plants.

•

Soil pH, CECe, and EC were significant and negative related to bioavailable and plant-Cd.

•

Ash content could be used as a guide for selecting biochars for Cd remediation.

Influence of Miscanthus Rhizome Pyrolysis Operating Conditions on Products Properties

Waste from the Miscanthus production cycle may be a promising source of material for the pyrolysis and biochar production. The biochar can be used to enrich the soil on which the crop grows, thus increasing productivity. A sample of Miscanthus rhizomes was used as a raw material in a series of experiments in order to find the most suitable conditions for the preparation of biochar. Miscanthus biochar was prepared in a laboratory unit using four different temperatures (i.e., 400, 500, 600 and 700 °C). All pyrolysis products were subsequently evaluated in terms of their quality and product yields were determined. For a temperature of 600 °C and a residence time of 2 h, the appropriate properties of biochar were achieved and the process was still economical. The biochar contained a minimal number of polycyclic aromatic hydrocarbons and a high percentage of carbon. Surface area was measured to be 217 m2/g. The aqueous extract of biochar was alkaline.

Evaluation of the Use of Sewage Sludge Biochar as a Soil Amendment—A Review

In recent decades, minimization and recycling/reuse policies were introduced to reduce the quantities of generated waste and for alternative waste recovery. Organic wastes represent 46% of total global solid waste. Possible uses of organic wastes include using it as fertilizer and amendment for soil, for energy recovery and for the production of chemical substances. Sewage sludge disposal and reuse are identified as future problems concerning waste. The total amount of sludge generated in the entire world has increased dramatically, and this tendency is expected to increase significantly in the years to come. In most developed countries, special attention is given to sewage sludge treatment in order to improve the quality and safety of using it on the ground surface. Sewage sludge pyrolysis is considered an acceptable method, from an economic and ecological perspective, for the beneficial reuse of sewage sludge. This method has many advantages because, during the pyrolysis process, the sludge volume is reduced by 80%, pathogenic agents and hazardous compounds from sewage sludge are eliminated, metals are immobilized in solid residue and organic and inorganic fractions are immobilized in a stabilized form of pyrolytic residues (biochar). The biochar generated by sewage sludge pyrolysis does not contain pathogenic agents and is rich in carbon and nutrients.

Calcite in combination with olive pulp biochar reduces Ni mobility in soil and its distribution in chili plant

The presence of Ni above the permissible limit in agriculture soils poses negative effects on soil health, crop quality, and crop productivity. Surprisingly, the usage of various organic and inorganic amendments can reduce Ni mobility in the soil and its distribution in the crops. A pot experiment was conducted to elucidate the effects of olive pulp biochar (BR), calcite (CAL), and wheat straw (WS), as sole amendments and their mixtures of 50:50 ratio, added to Ni polluted soil on Ni mobility in the soil, Ni immobilization index (Ni - IMi), soil enzymatic activities, Ni distribution in parts of chili plant, Ni translocation factor and bioaccumulation factor in fruit, plant growth parameters and oxidative stress encountered by the plants. Outcomes of this pot experiment revealed that amendments raised soil pH, improved soil enzymatic activities, values of Ni - IMi, while significantly reduced bioavailable Ni fraction in the post-harvest soil. However, the highest activities of acid phosphatase, urease, catalase, and dehydrogenase by 50, 70, 239, and 111%, respectively, improvement in Ni - IMi up to 60% while 60% reduction in the bioavailable Ni fraction was observed in BR + CAL treatment, compared to control was noted. Among all amendments, the top most reduction in Ni concentrations in shoots, roots, fruit, Translocation Factor (TF), and Bioaccumulation Factor (BAF) values of fruit by 72%, 36%, 86%, 72%, and 86%, in BR + CAL treatment, compared to control. Moreover, the plants growing on BR + CAL amended Ni contaminated soil showed the topmost improvement in plant phonological parameters while encountered the least oxidative stress. Such findings refer to the prospective usage of BR + CAL at 50:50 ratio than BR, CAL, WS alone, and BR + WS as well as WS + CAL for reducing Ni mobility in the soil, improving Ni - IMi, soil enzymatic activities, plant phonological and oxidative stress while reducing Ni distribution in plant parts. Novelty statementIn this experiment, it was hypothesized that amending Ni polluted soil with olive pulp biochar (BR), CAL, and WS as alone soil amendments and their combinations at 50:50 ratios can reduce Ni bioavailability in soil, Ni distribution in chili plant and oxidative stress encountered by the plants. Moreover, these amendments may improve, soil enzymatic activities, Ni immobilization index, plant phenological traits. Therefore, it was aimed to undertake useful scientific planning and research, to restore and rehabilitate the dwellings, biological resources and to minimize the sufferings of the peoples in nutrient-poor Ni contaminated soils, by improving soil health and chili productivity.

Potential of organic and inorganic amendments for stabilizing nickel in acidic soil, and improving the nutritional quality of spinach

Contamination of soils by nickel (Ni) has become a serious environmental problem throughout the world, and this substance wields dangerous effects on the ecosystem and food chain. A pot experiment was conducted to examine the effect of rice straw (RS), rice straw biochar (BI), and calcite (CC) at 1% and 2% application rates in a Ni-contaminated soil. The objective was to potentially stabilize Ni and reduce its bioavailability to spinach (Spinacia Oleracea L.). Spinach plants were grown in a Ni-contaminated Ultisol (commonly known as a red clay soil). Plant growth parameter results indicated that a BI 2% application rate significantly increased the root and shoots dry biomass increased by 1.7- and 6.3-fold, respectively, while essential nutrients were enhanced in the spinach plant compared to those in the untreated soil (CK). Moreover, adding amendments significantly decreased CaCl₂ extractable Ni by 62.5% 94.1%, and 87.2%, while the toxicity characteristics leaching procedure (TCLP) fell by 26.7%, 47.8%, and 41.7% when using RS, BI, and CC, respectively, at 2% compared to CK. The Ni concentrations in the spinach roots declined by 51.6%, 73.3%, and 68.9%, and in the shoots reduced by 54.1%, 76.7%, and 70.8% for RS, BI, and CC, at a 2% application rate, respectively. Bio-concentration factor (BCF) and translocation factor (TF) dropped significantly by as much as 72.7% and 20%, respectively, for BI 2% application rate. Results of the present study clearly indicated that biochar potential soil amendments for Ni stabilization, thereby reducing its bioavailability in the Ni-contaminated soil. This process enhanced the safety of food to be consumed and mitigated security risks.

Interactive effects of biochar and mussel shell activated concoctions on immobilization of nickel and their amelioration on the growth of rapeseed in contaminated aged soil

Mussel shell (MS) and biochar (BC) are commonly used for the remediation of metal contaminated soil. However, less research has been focused to examine the efficacy of their combinations to reduce metal toxicity in crop plants. This study was therefore conducted to investigate the effects of BC, MS and their activated concoctions on the soil properties, enzyme activities and nickel (Ni) immobilization in aged Ni contaminated soil. Moreover, the growth, photosynthetic pigments and anti-oxidative machnery of Brassica napus plants has also been investigated in order to determine amendments efficiency in reducing soil Ni toxicity for plants. The results showed that the application of Ni adversely affected soil health and trigged stress responses by inducing oxidative stress in B. napus. However, the incorporation of amendments reduced the bioavailability of Ni, and the concoctions of BC and MS showed promising results in the immobilization of Ni. Among various combinations of BC and MS, treatment with BC + MS (3:1) significantly reduced Ni uptake, decreased reactive oxygen species (ROS) and enhanced antioxidant defense of B. napus plants. Results showed that amendment's combinations stimulated the transcriptional levels of ROS scavenging enzymes and suppressed the expression level of Ni transporters. The morphological and physical characterization techniques (i.e. SEM, BET, EDS, FTIR and X-ray diffraction analyses) showed that amendment's combinations had relatively higher Ni adsorption capacity, indicating that BC and MS concoctions are efficient immobilizing agents for minimizing Ni availability, preventing oxidative toxicity and promoting growth and biomass production in rapeseed plants under metal stress conditions.

(Im)mobilization of arsenic, chromium, and nickel in soils via biochar: A meta-analysis

Biochar is a promising immobilizing agent of trace elements (TEs) in contaminated soils. However, several contradictory results have been reported regarding the potential of biochar to immobilize arsenic (As), chromium (Cr), and nickel (Ni) in contaminated soils. We conducted a meta-analysis on the published papers since 2006 until 2019 to examine the effects of biochar on the chemical (im)mobilization of As, Cr, and Ni in contaminated soils and to elucidate the major factors that control their interactions with biochar in soil. We synthesized 48 individual papers comprised of a total of 9351 pairwise comparisons and used the statistical tool of Cohen's d as an appropriate effect size for the comparison between means. We found that the application of biochar often increased the As mobilization in soils. Important variables that modulated the biochar effects on As mobilization in soil were pyrolysis temperature and time (ranging between 8 and 16 times when T > 450 °C and t > 1hr), organic matter (7-16 times when SOM<3%) and further site conditions. In contrast to As, biochar efficiently immobilized Cr and Ni in contaminated soils. The extent of the Cr and Ni immobilization was determined by the feedstock (Cr: 7-18 times for agricultural residue-derived biochar; Ni: 13-32 times for woody biomass-derived biochar). Our meta-analysis provides a compilation on the potential of different types of biochar to reduce/increase the mobilization of As, Cr, and Ni in various soils and under different experimental conditions. This study provides important insights on factors that affect biochar's efficiency for the (im)mobilization of As, Cr, and Ni in contaminated soils. While biochar effectively immobilizes Cr and Ni, a proper management of As-polluted soils with pristine biochar is still challenging. This limitation might be overcome by modification of biochar surfaces to exhibit higher surface area and functionality and active sites for surface complexation with TEs.

Agricultural Waste-Based Biochar for Agronomic Applications

Agricultural activities face several challenges due to the intensive increase in population growth and environmental issues. It has been established that biochar can be assigned a useful role in agriculture. Its agronomic application has therefore received increasing attention recently. The literature shows different applications, e.g., biochar serves as a soil ameliorant to optimize soil structure and composition, and it increases the availability of nutrients and the water retention capacity in the soil. If the biochar is buried in the soil, it decomposes very slowly and thus serves as a long-term store of carbon. Limiting the availability of pesticides and heavy metals increases soil health. Biochar addition also affects soil microbiology and enzyme activity and contributes to the improvement of plant growth and crop production. Biochar can be used as a compost additive and animal feed and simultaneously provides a contribution to minimizing greenhouse gas emissions. Several parameters, including biochar origin, pyrolysis temperature, soil type when biochar is used as soil amendment, and application rate, control biochar’s efficiency in different agricultural applications. Thus, special care should be given when using a specific biochar for a specific application to prevent any negative effects on the agricultural environment.

Arbuscular mycorrhizal fungi and pistachio husk biochar combination reduces Ni distribution in mungbean plant and improves plant antioxidants and soil enzymes

Soil pollution with nickel (Ni) casts detrimental effects on the quality of crops. Low-cost amendments can restrict Ni mobility in soil and its uptake by the plants. In this pot experiment, the effects of pistachio husk biochar (PHB) and arbuscular mycorrhizal fungi (AMF) on the distribution of Ni in mung bean and its bioavailability in Ni-spiked soil were evaluated. Plant parameters like Ni plant height, root dry weight, shoot dry weight, grain yield, chlorophyll contents, oxidative stress, Ni distribution in the roots, shoot, and grain, as well as the nutritional potential of grains, were measured on plants grown on Ni-contaminated soil amended or not (control) with AMF, zeolite (ZE), PHB, ZE + AMF, and PHB + AMF. Moreover, DTPA (diethylenetriamine pentaacetate)-extractable Ni in the soil, microbial biomass carbon (MBC), total glomalin (TG), extractable glomalin (EG), mycorrhizal root colonization (MRC), and the activities of soil enzymes (i.e. urease, acid phosphatase, and catalase) were also assessed after the plant harvest. With few exceptions, all treatments had significant effects on plant and soil parameters. The PHB + AMF treatment showed the topmost significant increment in plant physical parameters while reducing the Ni distribution in plant parts and oxidative injury. Based on these findings, it is proposed that PHB + AMF treatment can reduce Ni distribution and oxidative stress in mung bean plants and improve the biochemical compounds in grain.

Miscanthus biochar value chain - A review

To complete a loop of the Miscanthus value chain including production, phytomanagement, conversion to energy, and bioproducts, the wastes accumulated from these processes have to be returned to the production cycle to provide sustainable use of the feedstock, to reduce costs, and to ensure a zero-waste approach. This can be achieved by converting Miscanthus feedstock into biogas and biochar using pyrolysis and then returning biochar to the production cycle of Miscanthus crop applications in the phytotechnology of trace elements (TEs)-contaminated/marginal lands. These processes are subjects of the current review, which focused on the peculiarities of biochar received from Miscanthus by pyrolysis, its properties, the impact on soil characteristics, the phytoremediation process, biomass yield, and the abundance of soil biodiversity. Results from the literature indicated that the pH, surface area, and porosity of Miscanthus biochar are important in determining its impact on soil characteristics. It was inferred that the most effective Miscanthus biochar was produced with a pyrolysis temperature of about 600 °C with a residence time from about 30 min to an hour. Another important factor that determined the impact of Miscanthus biochar on soil health is the application rate: with its increase, the effect became more essential, and the recommended rate is between 5% and 10%. The influence of Miscanthus biochar on the TEs phytoremediation parameters is less studied, generally Miscanthus biochar produced at higher temperatures and added with higher application rates is more likely to restrict the mobility and availability of TEs by different plants. However, some published results are contradictory to these conclusions and showed absence of significant difference in TEs reduction during application of different Miscanthus biochar doses. The future experimental studies have to focus on determining the impact of a technological pyrolysis regime on Miscanthus biochar properties on TEs-contaminated or marginal land when biochar will be obtained from contaminated rhizomes and waste after the application of phytotechnology. In addition, studies must explore the influence of this biochar on TEs phytoparameters, enhancements in biomass yield, improvements in soil parameters, and the abundance of soil diversity.

Prospective usage of magnesium potassium phosphate cement combined with Bougainvillea alba derived biochar to reduce Pb bioavailability in soil and its uptake by Spinacia oleracea L

Combining biochar (BR) with other immobilizing amendments has additive effects on Pb immobilization and been recognized to be effective for the restoration of Pb polluted soils. However, the impacts of different proportions between BR and a highly efficient Pb immobilizing agent called "magnesium potassium phosphate cement (MC)" have never been earlier investigated. This work aimed to investigate the consequences of BR and MC alone and their mixtures of 25:75, 50:50, and 75:25 ratios on Pb bioavailability, Pb immobilization index (Pb-IMMi), and enzymatic activities in Pb polluted soil. Furthermore, amendments effects on Pb distribution in spinach, growth, antioxidant capacity, biochemical, and nutritional spectrum were also investigated. We found that MC alone performed well to immobilize Pb in soil and reducing its distribution in shoots, but was less efficient to improve soil enzymatic activities and plant attributes. Conversely, the application of BR alone stimulated soil enzymatic activities, plant growth, and quality but was less effective to immobilize Pb in soil and reducing shoot Pb concentrations. The combinations of BR and MC of various ratios showed variable results. Interestingly, the most promising outcomes were obtained with BR50%+MC50% treatment which resulted in enhanced Pb-IMMi (73%), activities of soil enzymes, plant growth and quality, and antioxidant capacity, compared to control. Likewise, significant reductions in Pb concentrations in shoots (85%), roots (78%), extractable Pb (73%) were also obtained with BR50%+MC50% treatment, compared to control. Such outcomes point towards a cost-effective approach for reducing Pb uptake by the plants via using MC and BR at a 50:50 ratio.

Chitosan with Bentonite and Biochar in Ni-Affected Soil Reduces Grain Ni Concentrations, Improves Soil Enzymes and Grain Quality in Lentil

Ecological and human health risks associated with Ni-affected soils are one of the major attention seeking issues nowadays. The current investigation is based on the usage of biochar (BR), chitosan (CN), bentonite (BE), and their mixture to immobilize Ni in a Ni-polluted soil and accordingly contracted Ni distribution in lentil plant parts, improved grain nutritional quality, antioxidant defense system, and soil enzymatic activities. The soil was initially amended with CN, BE, and BR and later lentil was grown in this soil in pots. Results depicted the highest significance of BE+CN treatment in terms of reducing the Ni distribution in the roots, shoots, grain, and DTPA-extractable fractions, relative to control treatment. Contrarily, the BR+CN treatment displayed the minimum oxidative stress and the utmost plant growth, chlorophyll contents in the leaves, relative water content (RWC), micronutrient concentrations, and grain biochemistry. The BR+CN indicated the highest activities of soil enzymes. Based on the results, we recommend BE+CN treatment to reduce the Ni distribution in the lentil plant. Although, improvement in plant growth, grain quality, soil enzymes, and a significant reduction in plant oxidative stress can only be gained with BR+CN.

Characterization of Chemically Activated Carbons Prepared from Miscanthus and Switchgrass Biomass

Lignocellulosic biomass, including that of energy crops, can be an alternative source to produce activated carbons (ACs). Miscanthus and switchgrass straw were used to produce ACs in a two-step process. Crushed plant material was carbonized at 600 °C and then obtained carbon was activated using NaOH or KOH at 750 °C. The content of surface oxygen groups was determined using Boehm’s method. The porosity of ACs was assayed using the nitrogen adsorption/desorption technique, while their thermal resistance using the thermogravimetric method. The ACs derived from miscanthus and switchgrass were characterized by surfaces rich in chemical groups and a highly developed porous structure. The highest specific surface areas, over 1600 m²/g, were obtained after carbon treatment with NaOH. High values of iodine number, 1200–1240 mg/g, indicate an extensive system of micropores and their good adsorption properties. The type of activator affected the contents of oxygen functional groups and some porosity parameters as well as thermal stability ranges of the ACs. Among obtained carbons, the highest quality was found for these derived from M. sacchariflorus followed by switchgrass, after activation with NaOH. Hence, while these crop species are not as effective biomass sources as other energy grasses, they can become valuable feedstocks for ACs.

Potential of pistachio shell biochar and dicalcium phosphate combination to reduce Pb speciation in spinach, improved soil enzymatic activities, plant nutritional quality, and antioxidant defense system

Lead-contaminated soils are becoming an ecological risk to the environment because of producing low-quality food which is directly causing critical health issues in humans and animals. We hypothesized that incorporation of dicalcium phosphate (DCP), eggshell powder (ESP) and biochar (BH) at diverse rates into a Pb-affected soil can proficiently immobilize Pb and decline its bioavailability to spinach (Spinacia oleracea L.). A soil was artificially spiked with Pb concentration (at 600 mg kg^-1) and further amended with DCP, ESP, and BH (as sole treatments at 2% and in concoctions at 1% each) for immobilization of Pb in the soil. The interlinked effects of applied treatments on Pb concentrations in shoots and roots, biomass, antioxidants, biochemistry, and nutrition of spinach were also investigated. Results depicted that the highest reduction in DTPA-extractable Pb and the concentrations of Pb in shoots and roots was achieved in DCP1%+BH1% treatment that was up to 58%, 66%, and 53%, respectively over control. Likewise, the DCP1%+BH1% treatment also showed the maximum shoot and root dry weight (DW), chlorophyll-a (Chl-a) and chlorophyll-b (Chl-b) contents and relative water content (RWC) in spinach up to 92%, 121%, 60%, 65%, and 30%, respectively, compared to control. Likewise, DCP1%+BH1% treatment noticeably improved antioxidant enzymes, biochemistry, and nutrition in the leaves. Moreover, the DCP1%+BH1% treatment depicted mostly enhanced activities of dehydrogenase, catalase, acid phosphatase, alkaline phosphatase, phosphomonoesterase, urease, protease and B-glucosidase in the post-harvested soil up to 118%, 345%, 55%, 92%, 288%, 107%, 53% and 252%, respectively over control.

Effect of rice straw, biochar and calcite on maize plant and Ni bio-availability in acidic Ni contaminated soil

Metals that contaminate soil is one of the major problems seriously affecting sustainable agriculture worldwide. Nickel (Ni) toxicity to agricultural crops is a global problem. Mobility of heavy metals present in contaminated soil can be reduced by the amendment of soil passivators, which will ultimately reduce the risk of them entering the food chain. A greenhouse pot experiment was conducted to investigate the effects of rice straw (RS), biochar derived from rice straw (BI) and calcium carbonate (calcite) on Ni mobility and its up take by maize (Zea maize L.) plant. Maize crop was grown in Ni spiked (100 mg kg^-1) soil with three application rates of passivators (equivalent to 0, 1and 2% of each RS, BI and calcite) applied separately to the soil. Results revealed that the post-harvest soil properties (pH, DOC and MBC), plant phenology (plant height, root length, total dry weight) and physiological characteristics were significantly enhanced with passivator application. Additionally, incorporating passivator into the soil reduced Ni mobility (DTPA) by 68%, 88.9% and 79.3%, and leachability (TCLP) by 72.4%, 76.7% and 66.7% for RS, BI and calcite, respectively at 2% application rate. The Ni concentration in the maize shoots reduced by 30%, 95.2% and 95% and in the roots by 56%, 66% and 63.8% with RS, BI and calcite at 2% application rate, respectively. These findings suggest that the application of 2% biochar (BI) is very promising in reducing Ni uptake, and can reduce toxicity to plants, decrease mobility and leachability in the soil.

Burkholderia phytofirmans PsJN and tree twigs derived biochar together retrieved Pb-induced growth, physiological and biochemical disturbances by minimizing its uptake and translocation in mung bean (Vigna radiata L.)

Anthropogenic activities like industrial mining, refining and smelting release substantial amounts of lead (Pb) into the soil causing potential ecological menaces to environment, soil productivity and food security. Present pot scale study was undertaken to investigate the effects of tree twigs-derived biochar and a bacterium Burkholderia phytofirmans PsJN on Pb accumulation, growth, physiological, biochemical and antioxidative defense responses of mung bean grown in Pb spiked soil. The original soil was spiked with Pb (600 mg kg^-1) and amended with biochar (1% w/w). Upon screening in laboratory, B. phytofirmans PsJN exhibited high Pb tolerance and was able to grow at high Pb concentrations. Surface-disinfected seeds of mung bean were inoculated with B. phytofirmans PsJN and sown in pots along with un-inoculated seeds. Data were collected for various growth, physiological and biochemical parameters from fully matured harvested plants. Application of biochar and B. phytofirmans PsJN ameliorated Pb induced negative impacts in mung bean both individually and in combination, but better growth, physiological and seed quality responses were observed with their combined use. Compared with respective controls, their combined use increased the following parameters in normal and Pb spiked soils, respectively: plant height (69% and 159%), root dry weight (97% and 130%), shoot dry weight (42% and 104%), number of pods (70% and 210%), grains weight (58% and 194%) and number of root nodules (71% and 255%). Moreover, combined use increased chlorophyll contents (27% and 37%), photosynthetic rate (93% and 204%), transpiration rate (42% and 132%), stomatal conductance (70% and 218%), sub-stomatal conductance (93% and 148%) and water use efficiency (35% and 43%). In addition, combined application of biochar and B. phytofirmans PsJN retarded Pb-induced oxidative stress by intensifying antioxidant enzyme activities and reducing activities of reactive oxygen species. Similarly, considerable reduction in Pb uptake, translocation and bioaccumulation in mung bean was noticed in Pb spiked soil due to applied amendments. Furthermore, their combined use resulted in considerable increase in grain quality parameters (protein, fat, ash) both in normal and Pb-spiked soils. Therefore, it can be inferred that interactive use of biochar and B. phytofirmans PsJN provides an efficient innovative strategy to repossess Pb induced growth, physiological, biochemical and oxidative disturbances in mung bean.

Application of wood biochar in polluted soils stabilized the toxic metals and enhanced wheat (Triticum aestivum) growth and soil enzymatic activity

Biochar is a stable carbonaceous by-product of pyrolysis and can be used for toxic metals (TMs) retention in polluted soil. Wheat (Triticum aestivum) was grown in three polluted soils collected from Chenzhou (CZ), Tongguan (TG) and Fengxian (FX), China. Wood biochar (WBC) was applied at 0, 0.5, 1.0 and 2.0% to each pot filled with 2 kg polluted soil. The results showed that WBC was efficient to alter soil pH and electrical conductivity (EC). The changes in soil pH and EC had a direct relationship with the immobilization and phytostabilization of TMs in the three soils. The bioavailable TMs (Zn, Pb, Cd, and Cu) were reduced in the soil after WBC amendments due to ion exchange, precipitates of metal-carbonates and metal-phosphates, and chemisorption on WBC surface. The reduction in the bioavailable TMs content also resulted in the diminution in TMs shoot uptake in wheat. Similarly, the TMs uptake in wheat root were also reduced as a result of WBC application. The reduction in bioavailable TMs and the release of essential nutrients and base cations from the WBC also increased the wheat shoot and root dry biomasses production. The application of WBC in polluted soil also improved soil health and the urease and β-glucosidase enzymes were also enhanced. The results concluded that WBC was efficient to reduce the bioavailability of TMs and shoot and root uptake, improved wheat dry biomasses production and soil enzymatic activities in industrial and smelter/mines polluted soils.

Confident performance of chitosan and pistachio shell biochar on reducing Ni bioavailability in soil and plant plus improved the soil enzymatic activities, antioxidant defense system and nutritional quality of lettuce

Nickel being a toxic heavy metal is considered as a hazardous pollutant in the soil environment. The cultivation of edible vegetables on Ni contaminated soil can deteriorate plant quality which causes critical health issues to humans and animals. Therefore, the remediation for such Ni polluted soils has currently become a great challenge for the researchers. Contrastingly, lowering bioavailability of Ni in those soils based on applying appropriate immobilizing amendments demonstrating a target to relieve virulence to plants can remarkably diminish the environmental hazard. In this experiment, biochar (BR) along diverse clays like bentonite (BE), cationic-zeolite (C-ZE), chitosan (CN) and attapulgite (AP) as individual doses at 2% each in a soil synthetically spiked with Ni (at 50 ppm) magnificently immobilize Ni and curtailed its bioavailability to lettuce (Lactuca sativa L.). In addition, the related influences of planned treatments on translocation of Ni to shoots and leaves, antioxidant preventive system over oxidative injury, biochemistry and nutritional ability of lettuce were monitored. Results suggested that the CN2% treatment performed excellently in terms of reducing Ni concentrations in leaves and roots of lettuce plants along bioavailable Ni in the soil after plant harvest. Surprisingly, the BR2% treatment efficiently promoted enzymatic activities in the soil and developed moisture content, photosynthesis, biomass, biochemistry, and nutrition (both micronutrients and macronutrients) and antioxidant preventive system while diminished Ni oxidative injury in lettuce plants over rest of the treatments. Finally, our results confirmed that individually applying CN at 2% in a Ni contaminated soil could significantly control Ni bioavailability, whereas, application of BR at 2% could remarkably develop aforementioned parameters in lettuce plants.

Effect of corn straw biochar application to sediments on the adsorption of 17α-ethinyl estradiol and perfluorooctane sulfonate at sediment-water interface

The immobilization of organic contaminants in sediment-water systems is of growing concern. Using biochar as sorbent amendment to reduce the mobility of pollutants in the sediment-water interface is becoming increasingly popular as a low-cost and environmentally friendly option. In this study, we mixed sediment from the Weishan Lake with biochar (0%, 2%, and 5% (w/w)) derived from corn straw to investigate the adsorption of perfluorooctane sulfonate (PFOS) and 17α-ethinyl estradiol (EE2). Biochar addition significantly improved the adsorption rates and capacities of EE2 and PFOS on sediments by the factors 1.7-3.5; the organic carbon concentration in the sediment was the main factor influencing this process. The sorption of EE2 and PFOS to sediment was near-linear (Freundlich exponent 1/n of 0.799-0.805), but non-linear for biochar (0.430-0.476) and sediment+biochar (0.370-0.421). The mobility of PFOS in the water-sediment system after biochar addition was significantly reduced, with a considerable increase (about three times) in the sediment-water distribution coefficient K_d. Compared to EE2, PFOS is anionic compound and contains hydrophobic C-F chains and hydrophilic S-O groups, making it more susceptible pH influences and resulting in interactions with-OH, -C=O, Si-O-Si, -O-Si, and -Al-O-Al groups via hydrogen bonding, ligand exchange, and surface complexation. We suggest that biochar amendment at ～5% is a viable approach to immobilize EE2 and PFOS at the sediment-water interface.

Effects of biochar and zeolite soil amendments with foliar proline spray on nickel immobilization, nutritional quality and nickel concentrations in wheat

Since Ni-rich soils are a threat to the environment, growing edible crops on Ni-rich soils can pose a serious risk to human, animal, plant and ecosystem health and, hence, is considered as a challenging task for the researchers. Contrarily, limiting the bioavailability of Ni in such soils upon the addition of suitable amendments cum foliar spray of proteinogenic amino acids having an objective to alleviate stress to crop plants can considerably reduce the environmental risk. In this pot trail, we substantiate the effects of biochar (BR) and zeolite (ZL) addition in the soil along with proline (PN) spray on the resistance, and stress responses of wheat against Ni as well as on Ni translocation and accumulation in wheat plants grown on a Ni-rich soil contaminated by electroplating effluent. The treatments, applied with and without PN spray, involved: no amendment; BR; ZL; and a concoction of both amendments (BR50%+ZL50%). We found that BR50%+ZL50% treatment significantly immobilized Ni in the soil, reduced its accumulation in the shoot, root, and grain, blocked membrane lipid peroxidation and showed an improvement in photosynthetic parameters, the status of antioxidant activities, grain biochemistry and grain yield, compared to the control. Interestingly, exogenous PN spray caused a significant additive effect on the aforementioned parameters in the wheat plants grown on BR50%+ZL50% treated soil. Our results involved a reduced Ni bioavailability in wheat rhizosphere due to BR50%+ZL50% in soil and, furthermore, the additive effect of PN spray to scavenging ROS, obstructing peroxidation of lipid membrane and, thus providing resilience to wheat plant against Ni stress. The suggested technique can make Ni-rich soils suitable for cultivation and production of high-quality food by minimizing Ni bioavailability and toxicity to plants.

Biochar-mediated sequestration of Pb and Cd leads to enhanced productivity in Mentha arvensis

Immobilization of cadmium (Cd) and lead (Pb) along with the alleviation of their phytotoxicity in Mentha arvensis by biochar was examined in this investigation. A greenhouse experiment was executed to evaluate the effect of biochar (BC) amended Cd and Pb spiked soil on their immobilization and uptake, plant growth, photosynthetic attributes (total chlorophyll, photosynthetic rate, transpiration rate, and stomatal activity) and oxidative enzymes (guaiacol peroxidase: POD; catalase: CAT and superoxide dismutase: SOD). In the present study, the photosynthetic attributes showed that BC significantly improved the total chlorophyll, photosynthetic, transpiration rates, and stomatal activity in the plants. The incorporation of BC in soil increase the Pb and Cd tolerance in M. arvensis vis-à-vis improved the biomass yield and nutrient intake. In addition, biochar has also reduced the POD, CAT, and SOD in the plant as well as improved the soil pH and enzymatic activities. Overall, BC immobilized the Cd and Pb in soil by providing the binding site to the metals and reduced the phytotoxicity in M. arvensis. However, large-scale field trials of BC are required for safe cultivation of M. arvensis which is known for its phytopharmaceuticals importance.

Biochar alleviates fluoride toxicity and oxidative stress in safflower (Carthamus tinctorius L.) seedlings

An original research was laid out as factorial to evaluate the possible effects of biochar (0, 25 and 50 g kg^-1 soil) on mitigating fluoride toxicity (non-contamination, 100, 200, 400 and 800 mg NaF kg^-1 soil) in safflower seedlings. Increasing fluoride toxicity up to 200 mg NaF kg^-1 soil did not decrease the safflower growth. However, the growth of plants under 400 and 800 mg NaF kg^-1 was reduced by enhancing soluble fluoride concentration in the soil. This growth reduction was the consequence of an increase in fluoride content of plant tissues, generation of super oxide radicals and hydrogen peroxide, lipid peroxidation, misbalancing potassium and calcium ions, and a decrease in synthesis of photosynthetic pigments including chlorophylls, carotenoids, anthocyanin, flavonoids and xanthophyll's and photochemical efficiency of photosystem II. Application of biochar decreased the fluoride solubility, fluoride content of plant tissues, oxidative stress and antioxidant enzymes activities, leading to an increase in cation exchange capacity of soil and the pH, calcium and potassium uptakes, maximum efficiency of photosystem II, synthesis of photosynthetic pigments, and plant growth. In general, addition of 50 g biochar to 1 kg soil was the best treatment for alleviation of the fluoride toxicity in safflower plants.

The effect of biochars application on reducing the toxic effects of nickel and growth indices of spinach (Spinacia oleracea L.) in a calcareous soil

Nowadays, production of biochar from agricultural wastes and its use for the amelioration of contaminated soils with heavy metals is increasing to reduce their negative effects on the growth of various plants. A factorial greenhouse experiment as a completely randomized design with three replications was performed to study the effect of different biochars on the spinach growth in a calcareous soil with different levels of nickel (Ni). The first factor consisted of biochars (control (CL), licorice root pulp (LRB), and rice husk (RHB) prepared at two pyrolysis temperatures (350 °C and 550 °C), each at 2.5% (w/w)), and the second factor included Ni application levels (0 (N₀), 150 (N₁), and 300 (N₂) mg kg^-1 soil). Shoot dry weight (15.0%), photosynthetic pigments (chlorophyll a (46.5%), b (39.5%), carotenoids (52.0%)), and micronutrients uptake (iron (51.8%), manganese (66.4%), copper (62.9%), and zinc (47.1%)) were decreased by increasing the Ni levels from N₀ to N₂. The activity of antioxidant enzymes (catalase (36.3%) and guaiacol peroxidase (29.3%)) and Ni uptake were increased by the Ni application levels. The biochar treatments (RHB350, RHB550, and LRB550) increased shoot dry weight of spinach through the reduction of Ni uptake, activity of antioxidant enzymes and enhancement of the micronutrients absorption. In general, the effect of the biochars produced at 550 °C on the reduction of Ni uptake and the increase in plant growth were better than the biochars produced at 350 °C. Finally, it could be concluded that the RHB550 is more suitable for reducing the Ni toxicity and improving the growth indices of the spinach.

Promoting the productivity and quality of brinjal aligned with heavy metals immobilization in a wastewater irrigated heavy metal polluted soil with biochar and chitosan

Depleting aquifers, lack of planning and low socioeconomic status of Pakistani farmers have led them to use wastewater (WW) for irrigating their crops causing food contamination with heavy metals and ultimately negative effects on human health. This study evaluates the effects of chitosan (CH) and biochar (BC) on growth and nutritional quality of brinjal plant together with in situ immobilization of heavy metals in a soil polluted with heavy metals due to irrigation with wastewater (SPHIW) and further irrigated with the same WW. Both CH and BC were applied at three different rates i.e. low rate [(LR), BC0.5%, CH0.5% and BC0.25%+CH0.25%], medium rate [(MR), BC1%, CH1% and BC0.5%+CH0.5%] and high rate [(HR), BC1.5%, CH1.5% and BC0.75%+CH0.75%]. Result revealed that brinjal growth, antioxidant enzymes, and fruit nutritional quality significantly improved from LR to HR for each amendment, relative to control. However, these results were more prominent with BC alone and BC+CH, compared with CH alone at each rate. Similarly, with few exceptions, significant reduction in Ni, Cd, Co, Cr and Pb concentrations in the root, shoot and fruit were found in sole CH treatment both at LR and MR but in both CH and BC+CH treatments at HR, relative to control. Interestingly, the concentrations of Fe in the roots, shoots and fruit were more pronounced at BC treatments relative to CH and BC+CH treatments at each rate, compared to control. Overall, the BC+CH treatment at HR was the most effective treatment for in situ immobilization of heavy metals in SPHIW and further irrigated with the same WW, compared to rest of the treatments. This study indicates that BC0.75%+CH0.75% treatment can be used to reduce mobility and bioavailability of heavy metals in SPHIW and facilitates plant growth by improving the antioxidant system. However, the feasibility of BC0.75%+CH0.75% treatment should also be tested at the field scale.

Improvement in productivity, nutritional quality, and antioxidative defense mechanisms of sunflower (Helianthus annuus L.) and maize (Zea mays L.) in nickel contaminated soil amended with different biochar and zeolite ratios

Nickel (Ni) contaminated soils pose a potential ecological risk to the environment, soil health, and quality of food produced on them. We hypothesized that application of miscanthus biochar (BC) and cationic zeolite (ZE) at various proportions into a Ni contaminated soil can efficiently immobilize Ni and reduce its bioavailability to sunflower (Helianthus annuus L.) and maize (Zea mays L.). An electroplating effluent contaminated soil was amended with BC and ZE, as sole treatments (2% w/w) and their combinations of various ratios (BC, ZE, BC25%ZE75%, BC50%ZE50% and BC75%ZE25%) for immobilization of Ni in the soil. Furthermore, the associated effects of these treatments on residual and DTPA-extractable Ni from the soil; concentrations of Ni in shoots, roots, and grain; growth, physiology, biochemistry and the antioxidant defence mechanisms of sunflower and maize were investigated. Results revealed that BC50%ZE50% treatment efficiently reduced DTPA-extractable Ni in the soil, Ni concentrations in shoots, roots, and grain, while improved selective parameters of both plants. Interestingly, the BC75%ZE25% treatment significantly improved the biomass, grain yield, physiology, biochemistry and antioxidant defense machinery, while decreased Ni oxidative stress in both sunflower and maize, compared to rest of the treatments. The results demonstrate that the BC50%ZE50% treatment can efficiently reduce Ni concentrations in the roots, shoots and grain of both sunflower and maize whereas, an improvement in biomass, grain yield, physiological, biochemical, and antioxidant defense machinery of both crops can only be achieved with the application of BC75%ZE25% treatment in a Ni contaminated soil.

Assessment of nickel bioavailability through chemical extractants and red clover (Trifolium pratense L.) in an amended soil: Related changes in various parameters of red clover

Application of immobilizing agents may efficiently reduce the bioavailability of nickel (Ni) in the soil. Here we report the effect of biochar (BC), gravel sludge (GS) and zeolite (ZE) as a sole treatment and their combinations on the bioavailability of Ni after their application into a Ni-polluted soil. The bioavailability of Ni after the application of immobilizing agents was assessed through an indicator plant (red clover) and chemical indicators of bioavailability like soil water extract (SWE), DTPA and Ca(NO₃)₂ extracts. Additionally, the effects of Ni bioavailability and immobilizing agents on the growth, physiological and biochemical attributes of red clover were also observed. Application of ZE significantly reduced Ni concentrations in all chemical extracts compared to rest of the treatments. Similarly, the combined application of BC and ZE (BC+ ZE) significantly reduced Ni concentrations, reactive oxygen species (ROS) whereas, significant enhancement in the growth, physiological and biochemical attributes along with an improvement in antioxidant defence machinery of red clover plant, compared to rest of the treatments, were observed. Furthermore, BC+ ZE treatment significantly reduced bioconcentration factor (BCF) and bioaccumulation factor (BAF) of Ni in red clover, compared to rest of the treatments. The Ni concentrations in red clover leaves individually reflected a good correlation with Ni concentrations in the extracts (SWE at R²=0.79, DTPA extract at R²=0.84 and Ca(NO₃)₂ extracts at R²=0.86). Our results indicate that combined application of ZE and BC can significantly reduce the Ni bioavailability in the soil while in parallel improve the antioxidant defence mechanism in plants.