Biochar for delivery of agri-inputs: Current status and future perspectives

Phytoremediation of mercury-contaminated Soil by Vigna radiata L. plant in companion with bacterial and fungal biofertilizers

Mercury is one of the most toxic pollutants that has drawn the attention of scientists. This study investigates the phytoremediation capabilities of Vigna radiata L. in conjunction with microbial biostimulators. The inoculated seeds were cultivated in soil under controlled greenhouse conditions. The concentration of Hg, biomass, and photosynthetic pigments was investigated under amendment factor including EDTA, bacterial, fungal (Mycorrhiza and Trichoderma), biochar, and combined levels, as well as the pollution factor with three levels of HgCl2 as two factorial experiments. Results showed that Plant Growth-Promoting Microorganisms (PGPMs) influenced mercury absorption and distribution in different plant organs. Aside from biochar, all stimulators increased the plant's Hg concentration. Although EDTA greatly increased mercury accumulation in plants, it reduced biomass. Fungal and bacterial treatments increased total mercury in the plant but decreased its concentration in the leaves. The combination of bacteria and fungi resulted in the highest mercury absorption, while the biochar in combination with PGPMs produced the greatest biomass. Analysis of mercury concentration in seeds indicated that V radiata effectively prevented its contamination in seeds. The results disclosed that microbial combinations of bacteria and fungi could increase the plant's potential to cope with heavy metal pollution. This improvement is due to the different roles of these two organisms, like nitrogen fixation by bacteria and phosphorus absorption by mycorrhiza fungi. Moreover, biochar as a soil amendment and microorganism carrier was noticed. Finally, considering the plant's inherent capacity to stabilize mercury in the roots, phytostabilization with the benefit of combined levels of biochar and microorganisms can be introduced as the best approach.

Analysis of the adsorption and fixation process of ammonium nitrogen in arable soil by biochar based on molecular dynamics simulation

The ammonia nitrogen in arable land soil is susceptible to environmental and anthropogenic influences, leading to nutrient loss. This study utilized indoor soil column leaching experiments, combined with adsorption mathematical models, traditional characterization methods, and molecular dynamics simulation methods, to analyze the effects of biochar on changes in ammonium ions in different soil layers and leachate of arable land soil. The study found that applying biochar at a ratio of 10 % to arable land soil could effectively increase the ammonium ion content in the 0-10 cm soil layer by 1.57-2.36 times and reduce loss by 44.83-72.27 %. The adsorption and fixation process of biochar is controlled by electrostatic attraction and ion exchange processes. Interactions between molecules, electrostatic forces, and system internal energy also have certain effects on the process. Near the structure of C6H12O6, there are low-energy adsorption sites for ammonium ions, which can provide the energy required for electrostatic attraction. Structures such as C5H10O5, C-S-H, C-SO3, and C4H7NO4 respectively play roles in physical adsorption or chemical adsorption through displacement reactions, electron exchange, and other forms. The adsorption free energy is -394,590.84 kcal/mol, indicating stable adsorption and a process that tends to interact with the biochar surface. This study addresses issues such as the easy loss of ammonia nitrogen in arable land soil and the unclear adsorption mechanism of biochar on ammonium ions, providing a theoretical basis for the field of environmental science.

Biopolymer as an additive for effective biochar-based rhizobial inoculant

Biochar is an efficient and inexpensive carrier for bacteria that stimulate plant development and growth. In this study, different biopolymer additives (cellulose, xanthan gum, chitin and tryptone) were tested with different addition ratios (1:0.1, 1:0.5 and 1:1) on further enhancing biochar capacity for supporting the growth and activity of Bradyrhizobium japonicum (CB1809). We utilized pine wood biochar (PWBC) pyrolyzed at 400 °C as the base inoculum carrier. The shelf life and survival rate of CB1809 were counted using the colony-forming unit (CFU) method for up to 120 days. Peat served as a standard reference material against which all treatments were compared. Subsequent experiments evaluated the ability of carrier inoculants to promote Glycine max L. (soybean) plant growth and nodulation under different watering regimes, i.e., 55 % water holding capacity (WHC) (D0), 30 % WHC (D1) and, 15 % WHC (D2) using sandy loam soil. Results revealed that among different additives; xanthan gum with 1:0.5 to PWBC [PWBC-xanthan gum(1:0.5)] was observed as a superior formulation in supporting rhizobial shelf life and survival rate of CB1809. In pot experiments, plants with PWBC-xanthan gum(1:0.5) formulation showed significant increase in various physiological characteristics (nitrogenase activity, chlorophyll pigments, membrane stability index, and relative water content), root architecture (root surface area, root average diameter, root volume, root tips, root forks and root crossings), and plant growth attributes (shoot/root dry biomass, shoot/root length, and number of nodules). Additionally, a reduced enrichment of isotopic signatures (δ13C, δ15N) was observed in plants treated with PWBC-xanthan gum(1:0.5), less enrichment of δ15N indicates an inverse link to nodulation and nitrogenase activity, while lower δ13C values indicates effective water use efficiency by plants during drought stress. These results suggest that biopolymers supplementation of the PWBC is useful in promoting shelf life or survival rate of CB1809.

Biotoxicity attenuation and the underlying physicochemical mechanism of biochar aged under simulated natural environmental conditions

Biochar (BC), with the benefits of enhancing soil fertility, absorbing heavy metals, carbon sequestration, and mitigating the greenhouse effect, has been extensively used for soil remediation. However, the long-term changes in the biotoxicity of BC under complex environmental conditions, which are the key factors influencing the sustainable application of BC in soil, are still unclear. Herein, the biotoxicity of BC aged with various processes, including dry‒wet cycle (DW) aging, freeze‒thaw cycle (FT) aging, ultraviolet irradiation (UV) aging, and low molecular weight organic acid (OA) aging, was systematically investigated by Escherichia coli (E. coli) culture experiments. The toxicity attenuation rate (%·week-1) was proposed to more concisely and clearly compare the influence of different aging methods on BC toxicity. The results indicated that after 5 weeks of aging, the toxicity attenuation rate during the four aging modes followed the order OA aging > FT aging > UV aging > DW aging. BC was nontoxic after 1 week of OA aging, 4 weeks of FT aging, 7 weeks of UV aging, and 14 weeks of DW aging. Spectroscopic characterizations revealed that humic acids in the dissolved organic matter of BC were the main reason for the biotoxicity. In addition, the attenuation of environmentally persistent free radicals on BC during aging was also an important factor for reducing environmental toxicity. This work provides insight into the detoxification mechanism of the BC aging process under ordinary environmental conditions and guidance for the safe application of BC in soil.

The fate and supply capacity of potassium in biochar used in agriculture

We used chemical extraction, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) to study the potassium (K) in biochar prepared from corn straw at different temperatures (300 °C, 500 °C, 700 °C and 900 °C). The characteristics of biochar were analyzed through Fourier transform infrared spectroscopy (FTIR) and specific surface area analysis. We found that the potassium in biochar can be divided into water soluble potassium, exchangeable potassium, non-exchangeable potassium, and insoluble potassium according to the availability of agricultural potassium. The fate of potassium in straw changed as follows: with increasing pyrolysis temperature, the proportion of the sum of exchangeable and non-exchangeable potassium decreased, and the proportions of insoluble and lost potassium increased. The total, water soluble and exchangeable potassium contents in biochar were highest at 700 °C. The non-exchangeable and insoluble potassium contents were highest at 300 °C and 900 °C, respectively. Kinetics experiments were conducted to determine the different fates of potassium released from biochar at different temperatures; pot experiments were also undertaken. The release of different forms of potassium in biochar at different temperatures is mainly dominated by heterogeneous diffusion. Biochar increased not only the content of different forms of potassium in soil but also the potassium content of soybean stems and leaves. We calculated the potassium supply capacity of biochar by two strategies, measurements of the potassium content in biochar and the conversion rate of potassium in straw during pyrolysis. The most active and efficient potassium supply capacities were 33.60 g·kg-1 and 9.53 g·kg-1 at 700 °C and 300 °C, respectively. Biochar provides readily available (water soluble and exchangeable) potassium and a long-term (non-exchangeable) potassium supply to soil.

Biochar Decreases Fertilizer Leaching and Promotes Miscanthus Growth in Saline-Alkaline Soil

Biochar has been widely reported to improve soil conditions and affect plant growth. However, its effectiveness is limited by soil type and production technology. Considering the application effect of biochar in saline alkali soil, there is currently a lack of in-depth mechanism explanations in the research. Therefore, we designed an experiment to explore the effect of biochar on plant growth in saline alkali soil and conducted soil column experiments in a greenhouse environment using composite inorganic fertilizer (NPK). The results showed that biochar significantly affected the distribution of soil nutrient content at different depths, with a significant increase in fertility levels in the surface and middle layers and a decrease in fertility levels in deep soils. Compared to using fertilizers alone, the combined use of biochar and fertilizers further expands the enrichment effect and significantly reduces the leaching of fertilizers into deeper layers. At the same time, the application of biochar also improved soil properties, including an increase in electrical conductivity and organic matter content, as well as an increase in soil enzyme activity. On the other hand, the application of biochar also increases the activity of antioxidant enzymes and the content of osmoregulation substances in plants, reducing the environmental stress that plants are subjected to. Therefore, our results indicate that biochar can reduce the leaching of fertilizers into deep soil layers, improve soil properties, and promotes the growth of Miscanthus in saline alkali soils.

Regulation and safety measures for nanotechnology-based agri-products

There is a wide range of application for nanotechnology in agriculture, including fertilizers, aquaculture, irrigation, water filtration, animal feed, animal vaccines, food processing, and packaging. In recent decades, nanotechnology emerged as a prospective and promising approach for the advancement of Agri-sector such as pest/disease prevention, fertilizers, agrochemicals, biofertilizers, bio-stimulants, post-harvest storage, pheromones-, and nutrient-delivery, and genetic manipulation in plants for crop improvement by using nanomaterial as a carrier system. Exponential increase in global population has enhanced food demand, so to fulfil the demand markets already included nano-based product likewise nano-encapsulated nutrients/agrochemicals, antimicrobial and packaging of food. For the approval of nano-based product, applicants for a marketing approval must show that such novel items can be used safely without endangering the consumer and environment. Several nations throughout the world have been actively looking at whether their regulatory frameworks are suitable for handling nanotechnologies. As a result, many techniques to regulate nano-based products in agriculture, feed, and food have been used. Here, we have contextualized different regulatory measures of several countries for nano-based products in agriculture, from feed to food, including guidance and legislation for safety assessment worldwide.

Potassium assisted pyrolysis of Chinese Baijiu distillers' grains to prepare biochar as controlled-release K fertilizer

A novel K-loaded biochar as controlled-release K fertilizer was prepared through K assisted pyrolysis of distillers' grains (DGs, typical solid-byproducts of Chinese Baijiu) under different atmospheres (N₂ and CO₂) and temperatures (400 and 800 °C). The fabricated DGs-based biochar exhibited high K loading (200.20-232.33 mg/g), and the release kinetics and column leaching experiments suggested that K-loaded biochar exhibited excellent controlled release performance in a long term. Compared with other biochar, the K-loaded biochar prepared at CO₂ and 400 °C has lower cumulative release ratio of 82.35 %, and could retain the durative K release at ~0.5 % for 25 d. The release kinetics suggested that the K release behavior was dominated by dissolution, electrostatic attraction, adsorption, confinement effect, and chemical interaction. Furthermore, pot experiments revealed that K-loaded biochar could promote the growth of Komatsuna, in which the fresh weight and chlorophyll relative content of Komatsuna cultivated with biochar prepared at CO₂ and 400 °C reached 0.146 g and 41.95 after 25 d growth, respectively. The above results suggested that the K-loaded biochar exhibited excellent utilization potential as a controlled-release K fertilizer, facilitating the sustainable development and resource valorization of Baijiu industry.

Nanocomposite-based smart fertilizers: A boon to agricultural and environmental sustainability

Fertilizers are indispensable agri-inputs to accomplish the growing food demand. The injudicious use of conventional fertilizer products has resulted in several environmental and human health complications. To mitigate these problems, nanocomposite-based fertilizers are viable alternative options. Nanocomposites, a novel class of materials having improved mechanical strength, barrier properties, and mechanical and thermal stability, are suitable candidates to develop eco-friendly slow/controlled release fertilizer formulations. In this review, the use of different nanocomposite materials developed for nutrient management in agriculture has been summarized with a major focus on their synthesis and characterization techniques, and application aspects in plant nutrition, along with addressing constraints and future opportunities of this domain. Further detailed studies on nanocomposite-based fertilizers are required to evaluate the cost-effective synthesis methods, in-depth field efficacy, environmental fate, stability, etc. before commercialization in the field of agriculture. The present review is expected to help the policy makers and all the stakeholders in the large-scale commercialization and application of nanocomposite-based smart fertilizer products with greater societal acceptance and environmental sustainability in near future.

Recovery of nitrogen and phosphorus in wastewater by red mud-modified biochar and its potential application

A large amount of wastewater containing nitrogen, phosphorus, and fluorine produces in the production of phosphate fertilizer. In this study, to simultaneously recover nitrogen and phosphorus from phosphorus-containing wastewater and realize the resource utilization of red mud and rape straw, red mud-modified rape straw biochar (RM/RSBC) was prepared by facile one step, and the physicochemical properties were characterized by Zeta potential, SEM-EDS, BET specific surface area (SSA), FTIR, XRD, and XPS. The adsorption performance and mechanisms of ammonium and phosphate onto RM/RSBC were explored through static, fixed-bed column adsorption, and practical wastewater experiments. The results showed that pH = 3.0 and 8.0 were favorable for the removal of phosphate and ammonium, respectively. The main adsorption mechanisms of ammonium and phosphate were the interaction between ammonium and surface functional groups and surface precipitation, respectively. The removal efficiencies of ammonium and phosphate by fixed-bed column adsorption mainly depended on the addition amount of RM/RSBC, the concentration of ammonium and phosphate, and the flow rate. The results of the germination experiment showed that adding > 0.5 wt% of RM/RSBC loaded with ammonium and phosphate promoted the growth of mung beans. This study shows that RM/RSBC can not only recover ammonium and phosphate in wastewater, but also realize the resource utilization of red mud and rape straw.

Synergistic removal of nitrate by a cellulose-degrading and denitrifying strain through iron loaded corn cobs filled biofilm reactor at low C/N ratio: Capability, enhancement and microbiome analysis

Optimization of nitrate removal rate under low carbon-to-nitrogen ratio has always been one of the research hotspots. Biofilm reactor based on functional carrier and using interspecific synergic effect of strains provides an insight. In this study, iron-loaded corn cob was used as a functional carrier that can contribute to the cellulose degradation, iron cycling, and collaborative denitrification process of microorganisms. During biofilm reactor operation, the maximum nitrate removal efficiency was 99.30% and could reach 81.73% at no carbon source. Dissolved organic carbon and carrier characterization showed that strain ZY7 promoted the release of carbon source. The crystallinity of cellulose I and II in carrier of experimental group increased by 31.26% and decreased by 21.83%, respectively, in comparison to the control group. Microbial community showed the synergistic effect among different strains. The vitality and metabolic activity of the target microorganisms in bioreactor were increased through interspecific bacterial cooperation.

Biochar combined with Bacillus subtilis SL-44 as an eco-friendly strategy to improve soil fertility, reduce Fusarium wilt, and promote radish growth

Bacillus subtilis as microbial fertilizers contribute to avoiding the harmful effects of traditional agricultural fertilizers and pesticides. However, there are many restrictions on the practical application of fertilizers. In this study, microbial biochar formulations (BCMs) were prepared by loading biochar with B. subtilis SL-44. Pot experiments were conducted to evaluate the effects of the BCMs on soil fertility, Fusarium wilt control, and radish plant growth. The application of BCMs dramatically improved soil properties and favored plant growth. Compared with SL-44 and biochar treatments, the BCMs treatments increased radish plant physical-chemical properties and activities of several enzymes in the soil. What's more, Fusarium wilt incidence had decreased by 59.88%. In addition, the BCMs treatments exhibited a significant increase in the abundance of bacterial genera in the rhizosphere soil of radish. Therefore, this study demonstrated that BCMs may be an eco-friendly strategy for improving soil fertility, reducing Fusarium wilt, and promoting radish plant growth.

Biochar surface properties and chemical composition determine the rhizobial survival rate

Biochar may be potentially used as a rhizobial carrier due to its specific chemical compositions and surface properties, but the relationship between these properties and rhizobial survival rate is largely unknown. Here, we analysed the physicochemical characteristics and carrier potential of six types of biochars made from various feedstocks at 600 °C using slow pyrolysis method, and results were compared with conventional carrier material peat. Liquid suspension of Bradyrhziobium japonicum CB1809 was used to inoculate all the carrier materials. Shelf life and survival rate was determined via colony forming unit (CFU) method for up to 90 days under two storage temperature conditions (28 °C and 38 °C). The determined physicochemical characteristics of biochars were categorized into major elements, trace elements, relative ratios, surface morphology, functional groups, and key basic properties; and their interaction to shelf life was analysed using hypothesis-oriented structure equation modelling (path analysis). Results revealed that different types of biochars had different capacity to impact on shelf life due to their different physicochemical properties. Among all biochars pine wood BC was the most suitable carrier with the highest counts of 10.11 Log 10 CFU g^-1 and 9.76 Log 10 CFU g^-1 at the end of 90 days at 28 °C and 38 °C storage, respectively. Path analysis revealed that rhizobial shelf life was largely explained by total carbon (TC), manganese (Mn), specific surface area (SSA), pore size, CO (ketonic carbon), and O-CO (carboxyl carbon) functional groups, and all these indicators exhibited positive direct impact on shelf life. Pinewood BC showed the highest values of Mn, SSA, pore size and functional groups (CO and O-CO), contributing to its highest rhizobial shelf life and survival rate among other biochars and peat tested.

Iron-modified biochar derived from sugarcane bagasse for adequate removal of aqueous imidacloprid: sorption mechanism study

Adsorption has been considered as a promising remediation technology to separate organic and inorganic agrochemicals from contaminated soil and water. Low-cost adsorbents, including waste derived materials, clay composites, biochar, and biochar modified materials, have attracted enormous attention for the removal of organic contaminants, including pesticides. In this study, iron-modified base-activated biochar (FeBBC) was prepared by pyrolysis (at 400 °C for 1 h) of iron-doped base (KOH) activated sugarcane bagasse for the removal of a widely used insecticide, namely imidacloprid (IMI) from water. The maximum adsorption capacity of the adsorbent (FeBBC) was calculated as 10.33 (± 1.57) mg/g from Langmuir isotherm model. The adsorbents could remove up to ~ 92% of IMI from aqueous solution at 23.8 mg/L IMI. Experimental data fitted well with the Freundlich model and pseudo-second-order model, demonstrating physisorption, as well as chemosorption, contributed to the sorption process. Even at highly acidic/basic solution pH, the FeBBC could remove substantial amount of IMI demonstrating hydrophobic interaction and pore diffusion play vital role for removal of IMI. The slight improving of IMI sorption with increasing solution pH indicated the sorption was also facilitated through ionic interaction alongside physical sorption. However, physical sorption including hydrophobic interaction and pore-filling interaction plays a vital role in the sorption of IMI.

Integrating Biochar, Bacteria, and Plants for Sustainable Remediation of Soils Contaminated with Organic Pollutants

The contamination of soil with organic pollutants has been accelerated by agricultural and industrial development and poses a major threat to global ecosystems and human health. Various chemical and physical techniques have been developed to remediate soils contaminated with organic pollutants, but challenges related to cost, efficacy, and toxic byproducts often limit their sustainability. Fortunately, phytoremediation, achieved through the use of plants and associated microbiomes, has shown great promise for tackling environmental pollution; this technology has been tested both in the laboratory and in the field. Plant-microbe interactions further promote the efficacy of phytoremediation, with plant growth-promoting bacteria (PGPB) often used to assist the remediation of organic pollutants. However, the efficiency of microbe-assisted phytoremediation can be impeded by (i) high concentrations of secondary toxins, (ii) the absence of a suitable sink for these toxins, (iii) nutrient limitations, (iv) the lack of continued release of microbial inocula, and (v) the lack of shelter or porous habitats for planktonic organisms. In this regard, biochar affords unparalleled positive attributes that make it a suitable bacterial carrier and soil health enhancer. We propose that several barriers can be overcome by integrating plants, PGPB, and biochar for the remediation of organic pollutants in soil. Here, we explore the mechanisms by which biochar and PGPB can assist plants in the remediation of organic pollutants in soils, and thereby improve soil health. We analyze the cost-effectiveness, feasibility, life cycle, and practicality of this integration for sustainable restoration and management of soil.

The effect of biochar on the migration theory of nutrient ions

As the acidification of arable soils increases, the utilization of nutrient ions such as N, P, and K decreases substantially. It causes environmental pollution and reduces crop yields. Through previous studies, acidified soil amendments have problems such as easy-retrograde and unclear mechanism. Therefore, in this study, biochar prepared by pyrolysis using peanut shells was used as a green amendment for acidified soil. Biochar with 0, 5 and 10 % biochar ratios were applied to the acidified soil, and the improvement and mechanism were investigated via experiments and software simulations. Analysis of the software simulation results revealed that biochar had the highest unit adsorption of K⁺ through physical adsorption at 820.38 mg/g. This was followed by PO₄^3-, NO₃^-, and NH₄⁺ as 270.51, 235.65 and 130.93 mg/g, respectively. These ions were controlled by both electrostatic and ion-exchange adsorption processes. During the improvement, the 10 % biochar ratio group performed the best with a 65.32 % reduction in the outlet volume, and the accumulated levels of nutrient ions in the leachate dropped by 48.40-68.28 % and increased by 437.80-913.87 % in the surface soil. Nutrient ion levels decreased gradually with the increase of soil depth, which agreed with the software simulation results. This study found that applying biochar to acidified soils can provide a solution to low nutrient utilization efficiency and unclear improvement mechanism of acidified soils, and provide a partial theoretical basis for the large-scale application of biochar. Future research on biochar for soil carbon sink and microbial expansion can be strengthened to contribute to environmental protection and multi-level utilization of energy.

Building a risk matrix for the safety assessment of wood derived biochars

Biochar is recognized as an efficient amendment and soil improver. However, environmental and quality assessments are needed to ensure the sustainability of its use in agriculture. This work considers the biochar's chemical-physical characterization and its potential phyto- and geno-toxicity, assessed with germination and Ames tests, obtaining valuable information for a safe field application. Three biochar types, obtained from gasification at different temperatures of green biomasses from the Tuscan-Emilian Apennines (in Italy), were compared through a broad chemical, physical and biological evaluation. The results obtained showed the relevance of temperature in determining the chemical and morphological properties of biochar, which was shown with several analytical techniques such as the elemental composition, water holding capacity, ash content, but also with FTIR and X-ray spectroscopies. These techniques showed the presence of different relevant surface aliphatic and aromatic groups. The procedures for evaluating the potential toxicity using seeds germination and Ames genotoxicity assay highlights that biochar does not cause detrimental effects when it enters in contact with soil, micro- and macro-organisms, and plants. The genotoxicity test provided a new highlight in evaluating biochar environmental safety.

Biochar-microorganism interactions for organic pollutant remediation: Challenges and perspectives

Numerous harmful chemicals are introduced every year in the environment through anthropogenic and geological activities raising global concerns of their ecotoxicological effects and decontamination strategies. Biochar technology has been recognized as an important pillar for recycling of biomass, contributing to the carbon capture and bioenergy industries, and remediation of contaminated soil, sediments and water. This paper aims to critically review the application potential of biochar with a special focus on the synergistic and antagonistic effects on contaminant-degrading microorganisms in single and mixed-contaminated systems. Owing to the high specific surface area, porous structure, and compatible surface chemistry, biochar can support the proliferation and activity of contaminant-degrading microorganisms. A combination of biochar and microorganisms to remove a variety of contaminants has gained popularity in recent years alongside traditional chemical and physical remediation technologies. The microbial compatibility of biochar can be improved by optimizing the surface parameters so that toxic pollutant release is minimized, biofilm formation is encouraged, and microbial populations are enhanced. Biocompatible biochar thus shows potential in the bioremediation of organic contaminants by harboring microbial populations, releasing contaminant-degrading enzymes, and protecting beneficial microorganisms from immediate toxicity of surrounding contaminants. This review recommends that biochar-microorganism co-deployment holds a great potential for the removal of contaminants thereby reducing the risk of organic contaminants to human and environmental health.

Experiment and Model Study on the Destination of 3,5,6-Trichloro-2-pyridinol in the Purple Soil of Southwestern China with a High Ratio of Biochar Applied

3,5,6-Trichloro-2-pyridinol (TCP), the main degradation production of the pesticide chlorpyrifos and the herbicide triclopyr, features anti-degradation and high water solubility that challenge the in situ prevention of the migration of TCP from soils to water bodies. Biochar is a widely used amendment, but previous studies focused on the low content of biochar application that restricted the off-site prevention. In this study, therefore, both experiments and models were employed to explore the destination of TCP in purple soil, an Entisol with low organic matter content, large pores, and high water conductivity in southwestern China with a high ratio of biochar applied. Soil columns were homogeneously packed by mixing biochar at 0, 1%, 2%, 3%, 4%, 5%, 7.5%, 10%, 15%, and 20%, then the impulsive input of the breakthrough curves was used to explore the adsorption and desorption process of TCP, and the release of adsorbed TCP was traced by Br−. Following the dynamic outflow during the adsorption processes was simulated using the cumulative distribution function of gamma distribution, and the release of TCP was simulated by coupling the mass balance equation and first-order decay kinetics equation. The results revealed that the adsorption ability of the soil increased exponentially with the content of mixed biochar, implying a much larger increment at high content. For the removal rate of 90%, e.g., the increment was about 20 mg/kg when the content of biochar was raised from 15% to 20%, while it was about 7 mg/kg when the content was raised from 0 to 5%. The dynamic release and the unreleasable TCP could be well simulated by the first-order decay kinetics equation and the logarithmic model, respectively. The releasable TCP showed an increase–decrease pattern, and the maximum was observed at a 5% biochar content. These results above will provide a systematic experimental scheme, model support, and data reference to control organic pollutants with high solubility, stability, and strong migration using biochar in an off-site pattern such as an ecological ditch system.

Low-temperature straw biochar: Sustainable approach for sustaining higher survival of B. megaterium and managing phosphorus deficiency in the soil

Inoculation of phosphate-solubilizing bacteria (PSB) is a sustainable approach to increase the available P content in soils for crop production. This application, however, is constrained by the low survival rate of PSB in the field. Biochar, a carbon-rich biomaterial with a well-developed porous structure, has recently emerged as an appealing option to maintain the population size of inoculants in the soil. The efficacy of biochar as a PSB carrier is primarily determined by its physicochemical properties, which are dominated by the feedstocks and the pyrolysis temperatures. This study demonstrated a comprehensive assessment of the efficacy of straw-derived biochars prepared from different feedstocks (i.e., crop straws from cotton, peanut, maize, soybean, and wheat) and pyrolysis temperatures (i.e., 300 and 600 °C). We employed B. megaterium carrying green fluorescence protein and evaluated its survival rate and phosphate-solubilizing performance in various inoculated biochars that have distinct physicochemical properties. Our results showed that the pyrolysis temperature is more determinant of the beneficial effect of straw biochar than the feedstock species. Cotton straw biochar pyrolyzed at low temperature (i.e., 300 °C) sustained a survival rate of 6.17% for the B. megaterium and thereby entailed a significant increase in available P in soil by 30.05 mg kg^-1 soil, which were nearly 18-fold and 8-fold higher than that of the no carrier treatment respectively. The performance of biochar-assisted PSB was dominant-negatively affected by the increasing pH, ash content, surface area, and total pore volume of biochar, while larger H/C ratio, water holding capacity, pore size, and surface hydrophobicity were predominantly conducive to the colonization and survival of PSB. The results of this study were expected to provide valuable guidance for biochar preparation in practice to enhance the survival and activity of PSB and maximize the utility of PSB as sustainable phosphorus fertilizer with economic applicability.

Establishing a quality management framework for commercial inoculants containing arbuscular mycorrhizal fungi

Microbial inoculants containing arbuscular mycorrhizal (AM) fungi are potential tools in increasing the sustainability of our food production systems. Given the demand for sustainable agriculture, the production of such inoculants has potential economic value and has resulted in a variety of commercial inoculants currently being advertised. However, their use is limited by inconsistent product efficacy and lack of consumer confidence. Here, we propose a framework that can be used to assess the quality and reliability of AM inoculants. First, we set out a range of basic quality criteria which are required to achieve reliable inoculants. This is followed by a standardized bioassay which can be used to test inoculum viability and efficacy under controlled conditions. Implementation of these measurements would contribute to the adoption of AM inoculants by producers with the potential to increase sustainability in food production systems.

Biochar application with reduced chemical fertilizers improves soil pore structure and rice productivity

Biochar is an efficient amendment to improve soil quality and crop productivity, but the potential of biochar as a substitute for chemical fertilizers is still unknown. Here we conducted a 6-year field experiment to investigate how partial substitution of biochar to NPK fertilizers affect soil quality and rice yield in the northeast of China. The experiment included three treatments: Control (B0: NPK fertilizers only: 240 kg N ha^-1, 52 kg P ha^-1, and 100 kg K ha^-1); Low-input biochar (B1.5: 95% N, 89% P, 75% K + 1.5 t biochar ha^-1 year^-1); and High-input biochar (B3.0: 90% N, 78% P, 50% K + 3.0 t biochar ha^-1 year^-1). The amounts of NPK application in the biochar treatments were determined according to an equivalent method. We evaluated the soil pore structure characteristics via a CT technology, and investigated soil nutrients, plant biomass, root growth, and grain yields. The results showed that, after the 6-year application, the soil pore structure and rice productivity of B1.5 were significantly improved in compared to those of B0 and B3.0. B1.5 had similar soil available NPK contents, but 6.6% higher rice yield as compared to B0, because of increased root length density (33.2%) and aboveground biomass (10.2%). B1.5 also increased soil macroporosity (>100 μm) (141.4%), fraction dimension (8.4%), and pore connectivity (16.6%) in compared with those of B0. However, B3.0 showed the lowest rice yield due to lower soil available N content (19.2%), macroporosity (28.5%), fraction dimension (5.5%), and pore connectivity (85.3%) than B0. This study demonstrated that a moderate NPK fertilizer replacement by biochar could be an effective practice that improves soil quality, increases rice growth and yield, and reduces the input of chemical fertilizers for rice production.

Biochar in environmental friendly fertilizers - Prospects of development products and technologies

According to the circular economy concept, the production of fertilizers should be closed in a loop, which prevents excessive emissions and harmful effects to the environment. Biological wastes are problematic to collect and transport. They undergo a biological transformation that causes greenhouse gases emission and sanitary hazards. Biomass sources used for organic or organo-mineral fertilizers must be free of pathogens and rich in macro and microelements. Solid residues can be processed thermally. Biochar is a carbon produced by biomass pyrolysis without oxygen presence and has been used for many years to improve soil quality and enhance the efficiency of fertilization. There are many research works on the use of biochar in fertilization. This study is also extended by the latest developments and technologies from the patent database (recent year) and biochar-based fertilizers market. To the best of our knowledge, there is no such review currently available in scientific databases. Based on the collected data, the best method of biochar management was proposed - soil application. Biochar applied to soil has several advantages: it improves soil structure and its sorption capacity, enhances soil-nutrient retention and water-holding capacity, immobilizes contaminants from soil (sorption), reduces greenhouse gas emissions and soil nutrient leaching losses while stimulating the growth of a plant.

Use of Biochar to Improve the Sustainable Crop Production of Cauliflower (Brassica oleracea L.)

In agriculture, biochar (B) application has been suggested as a green technology to reduce nitrate pollution from agricultural origins and improve crop yield. The agronomic impact of B use on soil has been extensively studied, while knowledge of its possible effects on horticultural cultivation is still scarce. A greenhouse experiment was conducted to evaluate the effect of using biochar in soils treated with two different rates of nitrogen fertilizers on soil properties and nitrogen (N) leachate. This study also investigated the vegetative parameters during the crop growing season of Brassica oleracea L. var. botrytis. Soil mesocosms were set up to test the following treatments: untreated/control (C); normal dose of N fertilizer (130 kg N ha^-1) (ND); ND+B; high dose of N fertilizer (260 kg N ha^-1) (HD); and HD+B. Principal component analysis and cluster analysis were exploited to assess biochar's ability to reduce nitrate leaching and enhance soil-vegetative properties. Biochar addition affected the soil chemical properties of the fertilized microcosms (ND and HD). Biochar increased the NH4+ content in HD soil and the NO3- content in ND soil by 26 mg/L and 48.76 mg/L, respectively. The results showed that biochar application increased the marketable cauliflower yield. In ND+B and HD+B, the curd weight was 880.68 kg and 1097.60 kg, respectively. In addition, a small number of nitrogenous compounds in the leachate were quantified in experimental lines with the biochar. Therefore, biochar use improves the marketable yield of horticulture, mitigating the negative impacts associated with the mass use of N fertilizers in agriculture.

Sorption, separation and recycling of ammonium in agricultural soils: A viable application for magnetic biochar?

Recent research on the magnetisation of biochar, a carbon-based material that can be used as a sorbent, has opened novel opportunities in the field of environmental remediation, as incorporating magnetic particles into biochar can simplify subsequent separation. This could offer a sustainable circular economy-based solution in two areas of waste management; firstly, pyrolysis of agricultural waste for magnetic biochar synthesis could reduce greenhouse gas emissions derived from traditional agricultural waste processing, such as landfill and incineration, while secondly, application of magnetic biochar to remove excess nitrogen from soils (made possible through magnetic separation) could provide opportunities for this pollutant to be used as a recycled fertiliser. While sorption of pollutants by magnetic biochar has been researched in wastewater, few studies have investigated magnetic biochar use in polluted soils. Nitrogen pollution (e.g. NH₄⁺), stemming from agricultural fertiliser management, is a major environmental and economic issue that could be significantly reduced before losses from soils occur. This review demonstrates that the use of magnetic biochar tailored to NH₄⁺ adsorption has potential to remove (and recycle for reuse) excess nitrogen from soils. Analysis of research into recovery of NH₄⁺ by sorption/desorption, biochar magnetisation and biochar-soil interactions, suggests that this is a promising application, but a more cohesive, interdisciplinary approach is called for to elucidate its feasibility. Furthermore, research shows variable impacts of biochar upon soil chemistry and biology, such as pH and microbial diversity. Considering wide concerns surrounding global biodiversity depletion, a more comprehensive understanding of biochar-soil dynamics is required to protect and support soil ecosystems. Finally, addressing research gaps, such as optimisation and scaling-up of magnetic biochar synthesis, would benefit from systems thinking approaches, ensuring the many complex considerations across science, industry, policy and economics are connected by circular-economy principles.

Technologies and perspectives for achieving carbon neutrality

Global development has been heavily reliant on the overexploitation of natural resources since the Industrial Revolution. With the extensive use of fossil fuels, deforestation, and other forms of land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (GHGs) in the atmosphere, causing global climate change. In response to the worsening global climate change, achieving carbon neutrality by 2050 is the most pressing task on the planet. To this end, it is of utmost importance and a significant challenge to reform the current production systems to reduce GHG emissions and promote the capture of CO2 from the atmosphere. Herein, we review innovative technologies that offer solutions achieving carbon (C) neutrality and sustainable development, including those for renewable energy production, food system transformation, waste valorization, C sink conservation, and C-negative manufacturing. The wealth of knowledge disseminated in this review could inspire the global community and drive the further development of innovative technologies to mitigate climate change and sustainably support human activities.

Integrated eco-strategies towards sustainable carbon and nitrogen cycling in agriculture

To meet the ever-growing human demands for food, fuel, and fiber, agricultural activities have dramatically altered the global carbon (C) and nitrogen (N) cycles. These biogeochemical cycles along with water, phosphorus, and sulfur cycles are fundamental features of life on Earth. Human alteration of the global N cycle has had both positive and negative outcomes. To efficiently feed a growing population, crop-livestock production systems have been developed, however, these systems also contribute significantly to environmental pollution and global climate change. Management of agricultural waste (AW) and the application of N fertilizers are central to the issues of greenhouse gas (GHG) emissions and nutrient runoff that contributes to the eutrophication of water bodies. If managed properly, AW can provide nutrients for plants and contribute to the conservation of soil health. In order to achieve the long-term conservation of agricultural production systems, it is important to promote the proper recycling of AW in agroecosystems and to minimize the reliance on chemical N fertilizers. Composting is one of the sustainable and effective approaches for recycling AW in agriculture. However, the conventional composting process is dilatory and produces compost with low N content compared to chemical N fertilizers. For this reason, comprehensive research is required to improve the composting process and the N content of the soil organic amendments. This work aims to explore the beneficial effects of the integrated application of biochar and specific C and N cycling microorganisms to the composting process and the quality of the composted products. In pursuit of replacing chemical N fertilizers with bio/organic fertilizers, we further discussed the power of the combined application of compost, biochar, and N-fixing bacteria in agricultural production systems. The knowledge of smart integration of AW and microorganisms in agriculture could solve the main agricultural and environmental problems associated with human-induced flows of C and N. Building upon the knowledge disseminated in review to further extensive research will pave the way for better management of agricultural production systems and sustainable C and N cycling in agriculture.

The Effects of Biochar on Indigenous Arbuscular Mycorrhizae Fungi from Agroenvironments

The effects of biochar on soil–plant–microorganisms systems are currently being extensively investigated. Considering that arbuscular mycorrhizal fungi (AMF) play an essential role in nutrient dynamics, the present study aims at understanding vine shoot-derived biochar effects on AMF activity and the impact of their multiplication in soils on water-stress resistance of plants. Three agronomic tests were performed in greenhouse pots. The first experiment evaluated the effects of three factors: final pyrolysis temperature for biochar production (400 °C and 600 °C), application rate (0 weight-wt.- % as a control, 1.5 wt. %, and 3.0 wt. %) and texture of the growing media (sandy-loam and clay-loam origin) on AMF, microbial communities and phosphatase activity. In the second experiment, an indigenous consortium of AMF was multiplied through the solid substrate method and sorghum as a trap plant with biochar addition. This process was compared to a control treatment without biochar. Obtained inocula were tested in a third experiment with lettuce plants under different water irrigation conditions. Results from the first experiment showed a general increase in AMF activity with the addition of the biochar produced at 400 °C in the sandy-loam texture substrate. Results of the second experiment showed that the biochar addition increased AMF root colonization, the number of AMF spores and AMF infective potential. Results of the third experiment showed that biochar-derived AMF inoculum increased AMF root colonization, AMF spores, dry biomass and the SPAD index in a lettuce crop under low-water irrigation conditions.

Biochar-bacteria-plant partnerships: Eco-solutions for tackling heavy metal pollution

Over the past 30 years, the ever-rising demands of the modern and growing population have led to the rapid development of agricultural and industrial sectors worldwide. However, this expansion has exposed the environment to various pollutants including heavy metal (HM)s. Almost all HMs are serious toxicants and can pose serious health risks to living organisms in addition to their bioaccumulative and non-biodegradable nature. Different techniques have been developed to restore the ecological functions of the HM-contaminated soil (HMCS). However, the major downfalls of the commonly used remediation technologies are the generation of secondary wastes, high operating costs, and high energy consumption. Phytoremediation is a prominent approach that is more innocuous than the existing remediation approaches. Some microbes-plant interactions enhance the bioremediation process, with heavy metal resistant-plant growth promoting bacteria (HMRPGPB) being widely used to assist phytoremediation of HMs. However, the most common of all major microbial assisted-phytoremediation disturbances is that the HM-contaminated soil is generally deficient in nutrients and cannot sustain the rapid growth of the applied HMRPGPB. In this case, biochar has recently been approved as a potential carrier of microbial agents. The biochar-HMRPGPB-plant association could provide a promising green approach to remediate HM-polluted sites. Therefore, this review addresses the mechanisms through which biochar and HMRPGPB can enhance phytoremediation. This knowledge of biochar-HMRPGPB-plant interactions is significant with respect to sustainable management of the HM-polluted environment in terms of both ecology and economy, and it offers the possibility of further development of new green technologies.