A quantitative understanding of the role of co-composted biochar in plant growth using meta-analysis

Application of municipal solid waste (MSW) char during rotary drum co-composting (RDC) of vegetable waste and its characterization

Composting, a sustainable method for handling biodegradable waste constituting nearly 50% of municipal solid waste (MSW), can be enhanced by incorporating char produced from MSW pyrolysis. This study investigates the impact of MSW char (0% char-Control, 2.5% char-Trial 1, 5% char-Trial 2) on the physicochemical properties of vegetable waste compost. A thermophilic temperature range of 53.8 °C was detected in Trial 2, 50.8 °C in Trial 1, and 46.8 °C in Control. The pH of the mixes increased at day 20 to 7.5, 7.87, and 8.2 in Control, Trial 1, and Trial 2, respectively. The highest drop of total organic carbon (TOC) and volatile solids in Trial 2 is about 21.18% and 21.02%, respectively. Total Kjeldahl nitrogen (TKN) increased, particularly in Trial 2 (2.35%), while NH4-N concentrations decreased, and phosphorus levels rose notably to 23.48 mg/kg, with 2.49 mg/kg available phosphorus in Trial 2. The C/N was reduced to 10 in Trial 2. Total potassium increase was highest for Trial 1 (6.9 g/kg). Trial 2 had the highest overall macronutrient concentration and correspondingly showed the greatest decrease in volatile solids. Furthermore, Trial 1 demonstrated a reduction in heavy metal concentration in comparison to Control and Trial 2. Consequently, the utilization of MSW char during rotary drum composting enhances the process of composting and significantly improves compost quality, making it a sustainable waste management solution.

Alternative crop residue management practices to mitigate the environmental and economic impacts of open burning of agricultural residues

Deliberate open burning of crop residues emits greenhouse gases and toxic pollutants into the atmosphere. This study investigates the environmental impacts (global warming potential, GWP) and economic impacts (net cash flow) of nine agricultural residue management schemes, including open burning, fertilizer production, and biochar production for corn residue, rice straw, and sugarcane leaves. The environmental assessment shows that, except the open burning schemes, fossil fuel consumption is the main contributor of the GWP impact. The fertilizer and biochar schemes reduce the GWP impact including black carbon by 1.88-1.96 and 2.46-3.22 times compared to open burning. The biochar schemes have the lowest GWP (- 1833.19 to - 1473.21 kg CO2-eq/ton). The economic assessment outcomes reveal that the biochar schemes have the highest net cash flow (222.72-889.31 US$2022/ton or 1258.15-13409.16 US$2022/ha). The expenditures of open burning are practically zero, while the biochar schemes are the most costly to operate. The most preferable agricultural residue management type is the biochar production, given the lowest GWP impact and the highest net cash flow. To discourage open burning, the government should tailor the government assistance programs to the needs of the farmers and make the financial assistance more accessible.

Biochar and nano biochar: Enhancing salt resilience in plants and soil while mitigating greenhouse gas emissions: A comprehensive review

Salinity stress poses a significant challenge to agriculture, impacting soil health, plant growth and contributing to greenhouse gas (GHG) emissions. In response to these intertwined challenges, the use of biochar and its nanoscale counterpart, nano-biochar, has gained increasing attention. This comprehensive review explores the heterogeneous role of biochar and nano-biochar in enhancing salt resilience in plants and soil while concurrently mitigating GHG emissions. The review discusses the effects of these amendments on soil physicochemical properties, improved water and nutrient uptake, reduced oxidative damage, enhanced growth and the alternation of soil microbial communities, enhance soil fertility and resilience. Furthermore, it examines their impact on plant growth, ion homeostasis, osmotic adjustment and plant stress tolerance, promoting plant development under salinity stress conditions. Emphasis is placed on the potential of biochar and nano-biochar to influence soil microbial activities, leading to altered emissions of GHG emissions, particularly nitrous oxide(N2O) and methane(CH4), contributing to climate change mitigation. The comprehensive synthesis of current research findings in this review provides insights into the multifunctional applications of biochar and nano-biochar, highlighting their potential to address salinity stress in agriculture and their role in sustainable soil and environmental management. Moreover, it identifies areas for further investigation, aiming to enhance our understanding of the intricate interplay between biochar, nano-biochar, soil, plants, and greenhouse gas emissions.

Biochar-based organic fertilizers: Influence on yield and concentration of antioxidants in the stigma of saffron and rhizosphere bacterial diversity of slightly saline and non-saline soils

Being the most expensive spice, saffron has great economic importance. This crop grows well in cold arid deserts. Salinity is one of the important limiting factors for the cultivation of this crop. However, the use of composted manured and co-composted biochar and fertilizers can play a role in attenuating the salinity stress on this crop. In this two-year field study, manures from three sources: sheep and goat (SG), cow and buffalo (FYM), and poultry (PM) farms, and their co-compost with slow-pyrolyzed wood-derived biochar (B) were used for saffron cultivation in slightly saline (electrical conductivity 1.95 dS m-1) and non-saline soils. Yield and concentration of antioxidants of stigma and bacterial diversity in the rhizosphere of this crop, under salinity and non-salinity conditions, were evaluated. Results revealed that in non-saline soil of first-year crops, all fertilizers decreased the yield of stigma than control by 15-49 % (P ≤ 0.05) but increased the concentration of carotenoids and total polyphenolics (P ≤ 0.05). In saline soil, no difference in yield was observed between treatments for the first-year crop; however, for the second-year crop, as compared to control, PM and FYM significantly increased yield by 41 % and 44 % respectively, whereas FYM also increased the concentration of total polyphenolics (P ≤ 0.05). The FYM fertilizer was found suitable for the yield and quality of saffron stigma for second-year crops in both soils (non-saline and saline). The observed OTUs, Chao1, Fischer, and ACE indexes based on 16 s rRNA metagenomic analysis revealed 2-4 times greater bacterial diversity in the rhizosphere soil of PM-B and SG-B treatments than in the control. Furthermore, 347 bacterial species were found in PM-B- or SG-B-amended soils absent in control treatments.

Exploring negative emission potential of biochar to achieve carbon neutrality goal in China

Limiting global warming to within 1.5 °C might require large-scale deployment of premature negative emission technologies with potentially adverse effects on the key sustainable development goals. Biochar has been proposed as an established technology for carbon sequestration with co-benefits in terms of soil quality and crop yield. However, the considerable uncertainties that exist in the potential, cost, and deployment strategies of biochar systems at national level prevent its deployment in China. Here, we conduct a spatially explicit analysis to investigate the negative emission potential, economics, and priority deployment sites of biochar derived from multiple feedstocks in China. Results show that biochar has negative emission potential of up to 0.92 billion tons of CO2 per year with an average net cost of US$90 per ton of CO2 in a sustainable manner, which could satisfy the negative emission demands in most mitigation scenarios compatible with China's target of carbon neutrality by 2060.

Mathematical modeling of biochar's role in elevating co-composted poultry carcass temperatures

Previous studies reported that incorporating biochar into composting systems leads to an increase in compost temperatures. Although potential reasons, such as improved microbial activity or increased insulation, were suggested, no study has quantitatively determined the contribution of either aspect. In this study, we developed a heat transfer model for a biochar-amended co-composting system based on the measurements from our two previously published studies conducted to co-compost poultry carcasses with woodchips and wood-based (WBC), distillers grain (DGBC), and cow manure (CMB) biochar. The two composting studies were conducted over three heating cycles, with two turnings separating each cycle. The simulation for the second heating cycle, during which the compost materials began to degrade and were well-mixed, showed an average R2 value of 0.86 and was selected for further analyses. Results from the model suggested that incorporating biochar into the composting mixture increases thermal conductive losses. For example, at a biochar addition rate of 13 % (v/v), the predicted longitudinal conductive resistance of the compost pile was reduced by 24.9 %. However, the total heat unit still increased by 11.2 ± 3.17 % due to the enhancement of microbial activity as supported by elevated oxygen consumption (38.1-61.1 %). When biochar was applied in layers on the surface of the composting bins, its impact on microbial activity was minimal, primarily functioning as an insulator. Under these conditions, the total heat unit was 8.7 % higher than the control. These findings suggest that biochar's primary effect on temperature development was through promoting microbial activity.

Co-composting of digestate and garden waste with biochar: effect on greenhouse gas production and fertilizer value of the matured compost

Biogas digestate is a nitrogen (N) rich waste product that has potential for application to soil as a fertilizer. Composting of digestate is recognized as an effective step to reduce potentially negative consequences of digestate application to soils. However, the structure of the digestate and the high N content can hinder effective composting. Biochar, which can be produced through the pyrolysis of waste biomass, has shown the potential to improve compost structure and increase N retention in soils. We studied how a high-temperature wood biochar affects the composting process, including greenhouse gas emissions, and the fertilizer value of the compost product including nutrient content, leachability and plant growth. The high Biochar dose (17% w/w) had a significantly positive effect on the maximum temperature (5°C increase vs. no biochar) and appeared to improve temperature stability during composting with less variability between replicates. Biochar addition reduced cumulative N2O emission by 65-70%, but had no significant effect on CO2 and CH4 emission. Biochar did not contribute to greater retention of nitrogen (N) contained in the digestate, but had a dilution effect on both N content and mineral nutrients. Fertilization with compost enhanced plant growth and nutrient retention in soil compared to mineral fertilization (NPK), but biochar had no additional effects on these parameters. Our results show that biochar improves the composting of digestate with no subsequent negative effects on plants.

Improved remediation of amoxicillin-contaminated water by floating treatment wetlands intensified with biochar, nutrients, aeration, and antibiotic-degrading bacteria

Residual antibiotics have become emerging contaminants of concern for their adverse impact on the ecosystem. Additionally, their accumulation in the environment is increasing antibiotic resistance among pathogens. This study assessed the impact of intensification of biochar, nutrients, aeration, and bacteria (BNAB) on the remediation potential of floating treatment wetlands (FTWs) to treat amoxicillin (AMX)-contaminated water. The FTWs were developed with saplings of Vetiveria zizanioides and intensified with biochar (1.5%), nutrients (25 mgL-1 N, 25 mgL-1 P, 20 mg L1 K), aeration (7 mg L-1), and AMX-degrading bacteria. The results showed that all the amendments enhanced the AMX degradation, while the maximum reduction in COD (89%), BOD (88%), TOC (87%), and AMX (97%) was shown by the combined application of all the amendments. The combined application also enhanced plant growth and persistence of the inoculated bacteria in the water, roots, and shoots. This approach can be employed for the low-cost, environment-friendly treatment, and recycling of antibiotic-contaminated wastewater, where BNAB intensification can further improve the bioremediation efficiency of FTWs in the case of heavily polluted waters.

Biochar and Chlorella increase rice yield by improving saline-alkali soil physicochemical properties and regulating bacteria under aquaculture wastewater irrigation

The combined effects of biochar and Chlorella under aquaculture wastewater irrigation in improving saline-alkali soil physicochemical properties, microbial communities, and rice yield, is not yet clear. This study utilized soil physicochemical indicators and gene sequencing to examine the effect of salinity stress, biochar and Chlorella under aquaculture wastewater irrigation on soil properties, bacterial community compositions, and rice production. Treatments included three factors in a randomized complete block design with three replications: (i) Biochar - 40 tons ha -1 (BW) versus no-biochar (BN); (ii) Salinity - 3‰ salinity (SH) versus 1‰ salinity (SL); and (iii) Chlorella - with 107 cells mL -1 Chlorella (CW) versus no-Chlorella (CN). The results revealed that increased salinity adversely affected the soil nutrients (TOC, NO3⁻-N, NH4+-N, Olsen-P), and enzyme activity (urease, sucrase, catalase), resulting in a 9.67% reduction in rice yield compared to SL treatment. However, the close correlation between alterations in soil bacterial communities, functions, and soil physicochemical properties, as well as rice yield, indicated that biochar and Chlorella promoted rice yield by enhancing the physicochemical properties of saline-alkali soil and bacterial community when irrigated with aquaculture wastewater: (1) addition of biochar increased the146.05% rice yield by increasing TOC content, the complexity of bacterial co-occurrence patterns, nitrogen fixation potential, and nitrification potential, (2) addition of Chlorella increased TOC, NO3⁻-N, NH4+-N, enhanced urease, sucrase, catalase activity, and nitrification potential to increased rice yield by 60.29%, and (3) compared with the treatment T3 (SHBNCN), the treatments with biochar (BW) and Chlorella (CW) increased the yield by 561.30% and 445.03% under 1‰ and 3‰ salinity, respectively. These findings provide novel perspectives on the capacity of biochar and Chlorella to improve saline-alkali soil properties and increase rice yield irrigated with aquaculture wastewater.

Investigating the role of bulking agents in compost maturity

Kitchen waste is increasing globally, similarly in Pakistan bulk of municipal solid waste comprises of kitchen waste specifically, tea waste. Composting of kitchen waste is one of the promising ways to convert waste into useful product, resulting into zero waste. This study is aimed to convert waste (kitchen waste) in to a resource (compost) using bulking agents (tea waste and biochar) for reducing maturity time. Secondly, compost application on Solanum lycopersicum (tomato) was also tested. Four compost treatments were designed under aerobic composting conditions for 30 days. Tea waste and biochar have accelerated the maturity rate and produced a nutrient rich compost. Final compost had Electrical Conductivity of 2mS/cm, Carbon Nitrogen ration of 15, 54% of organic matter, 15% of moisture content, 48% of cellulose content, and 28% of Lignin content. With the use of Co-compost the Solanum lycopersicum showed 133% germination index, 100% germination, 235% Munoo-Liisa Vitality Index and 1238% seed vigor index. Co-compost also improved the soil total nitrogen by 1.4%, total phosphorous by 2%, total potassium by 2.1% and bulk density by 2.6 gcm-3. This study successfully used tea waste and biochar as bulking agents to reduce maturation time to 30 days. Tea waste and biochar enhanced the organic matter degradation, lignocellulose degradation, water holding capacity, porosity, seed's vigor, germination index. This research can be helpful in developing home composting and home gardening to combat solid waste management and food security issue in developing countries.

Biochar-amended compost as a promising soil amendment for enhancing plant productivity: A meta-analysis study

A meta-analysis was conducted to evaluate the effect of biochar-amended compost (BAC) on plant productivity (PP) and soil quality. The analysis was based on observations from 47 peer-reviewed publications. The results showed that BAC application significantly increased PP by 74.9 %, the total nitrogen content of soil by 37.6 %, and the organic matter content of soil by 98.6 %. Additionally, BAC application significantly decreased the bioavailability of cadmium (-58.3 %), lead (-50.1 %), and zinc (-87.3 %). However, the bioavailability of copper increased by 30.1 %. The study explored the key factors regulating the response of PP to BAC through subgroup analysis. It was found that the increase in the organic matter content of the soil was the key mechanism for PP improvement. The recommended rate of BAC application for improving PP was found to be between 10 and 20 t ha^-1. Overall, the findings of this study are significant in providing data support and technical guidance for the application of BAC in agricultural production. However, the high heterogeneity of BAC application conditions, soil properties, and plant types suggests that site-specific factors should be considered when applying BAC to soils.

Meeting the heavy-metal safety requirements for food crops by using biochar: An investigation using sunflower as a representative plant under different atmospheric CO2 concentrations

Global warming impacts on plant growth and food safety are emerging topics of concern, while biochar as a soil additive benefits plants. This study investigates (1) sunflower plant growth at various biochar concentrations in a soil-compost growing substrate under both ambient (420 ppm) and elevated (740 ppm) atmospheric CO₂ concentrations, and (2) concentrations of heavy metals in the growing substrates and organs of the plants. The elevated CO₂ concentration benefits the vegetative parts but harms the reproductive parts of the plants. Additionally, the elevated CO₂ concentration inhibits the beneficial effects that biochar confers on the plants at the ambient concentration. The optimum biochar concentration at both CO₂ levels was found to be 15%. At the time of harvest, most of the heavy-metal concentrations in the growing substrate increased. It was demonstrated that biochar can reduce the amount of heavy metals that accumulate in the roots and seeds whose heavy-metal concentrations complied with Singapore food safety regulations, while those for the biochar met the proposed Singapore biochar standard's thresholds. Our results show that the proposed Singapore biochar standard is practical and sound.

The Effects of Two Organic Soil Amendments, Biochar and Insect Frass Fertilizer, on Shoot Growth of Cereal Seedlings

To mitigate the environmental harm associated with high-input agriculture, arable farmers are increasingly required to maintain productivity while reducing inputs of synthetic fertilizers. Thus, a diverse range of organic products are now being investigated in terms of their value as alternative fertilizers and soil amendments. This study used a series of glasshouse trials to investigate the effects of an insect frass-based fertilizer derived from black soldier fly waste [HexaFrass™, Meath, Ireland] and biochar on four cereals grown in Ireland (barley, oats, triticale, spelt) as animal feed and for human consumption. In general, the application of low quantities of HexaFrass™ resulted in significant increases in shoot growth in all four cereal species, along with increased foliage concentrations of NPK and SPAD levels (a measure of chlorophyll density). These positive effects of HexaFrass™ on shoot growth were observed, however, only when a potting mix with low basal nutrients was used. Additionally, excessive application of HexaFrass™ resulted in reduced shoot growth and, in some cases, seedling mortality. The application of finely ground or crushed biochar produced from four different feedstocks (Ulex, Juncus, woodchip, olive stone) had no consistent positive or negative effects on cereal shoot growth. Overall, our results indicate that insect frass-based fertilizers have good potential in low-input, organic, or regenerative cereal production systems. Based on our results, biochar appears to have less potential as a plant growth promoting product, but could be used as a tool for lowering whole-farm carbon budgets by providing a simplistic means of storing carbon in farm soils.

Response of water-biochar interactions to physical and biochemical aging

Biochar aging may affect the interactions of biochar with water and thus its performance as soil amendment; yet the specific mechanisms underlying these effects are poorly understood. By means of FTIR, N₂ adsorption, Hg intrusion porosimetry, thermogravimetric analysis, ¹³C solid state nuclear magnetic resonance (NMR) and ¹H NMR relaxometry, we investigated changes in the chemistry and structure of biochar as well as its interaction with water after biochar aging, both physical (simulated by ball-milling) and biochemical (simulated by co-composting). Three different porosities of biochar were examined: <5 nm, 1 μm and 10 μm diameter sizes. Physical aging caused the disappearance of the porosity at 10 μm. With biochemical aging, biochar underwent an enrichment of oxygenated functional groups either as a result of surface functionalisation processes or by the deposition of fresh organic matter layers on the surface and pores of biochar. ¹H NMR relaxometry revealed that the proportion of water strongly interacting with biochar increased with both physical and biochemical aging. Although biochemical aging significantly altered the composition of biochar surface and modulates its interaction with water, ¹H NMR relaxometry proved that physical aging had a relatively stronger influence on water mobility and dynamics in biochar, lowering both T₁ and T₂ relaxation times in the initial contact times of biochar and water.

Profitability and agronomic potential of cotton (Gossypium hirsutum L.) under biochar-compost-based amendments in three agroecological zones of northern Benin

Low land productivity is a major constraint facing agriculture in sub-Saharan Africa, which severely affects crop yields, particularly cotton which is main export agricultural produce of Northern Benin. To overcome this situation, the hill-placement of microdose biochar-compost-based amendments was carried out at two research stations and on farmer's fields in three agroecological zones of northern Benin. The study aims to evaluate the agronomic and economic performance of cotton under two types of compost and biochar-based amendments. On stations, the experimental design used was a complete randomized block with one factor and ten treatments replicated four times as follows: (i) absolute control without any amendment (Ck), (ii) mineral fertilizer (MF) at 200 kg/ha, (iii) cow dung-based compost at 200kg/ha (CP1_200) and (iv) 300kg (CP1_300), (v) household waste-based compost at 200kg/ha (CP2_200) and (vi) 300 kg (CP2_300), the combination of CP1 and 15% biochar designated Terra preta (TP) applied at 200kg/ha (vii, TP1_200) and 300kg/ha (viii, TP1_300), the combination of CP2 and 15% biochar applied at 200kg/ha (ix, TP2_200) and 300kg/ha (x, TP2_300). On-farms, the experimental design was a randomized complete block with one factor and six optimal treatments extracted from the on-station experiments with three replicates installed in four farmers' fields from each location studied. The six treatments were: Ck, MF, CP1_200, CP2_200, TP1_200 and TP2_200. Cotton growth (Plant height, number of vegetative and reproductive branches and total bolls per plant) and yield data were collected. The treatment TP1_300 yielded higher cotton seed with 2.53 t/ha, i.e., 86% more than the absolute control. However, the highest plant growth parameters were obtained with MF which were similar to those obtained with TP1_300 (P &gt; 0.05). Likewise, at farms, the highest plant growth parameters and yield were observed with MF followed by TP1_200 (with a cotton seed yield increase of 146% compared to the control, P &lt; 0.05). In addition, no significant differences were observed between organic fertilizers treatments for growth variables. However yield differences occurred. To resume, TP1_300 kg/ha performed best in terms of growth and yield in on-station experiments, while on-farms, TP1_200 kg/ha produced the highest responses of cotton. Value Cost Ratio (VCR) and Benefit Cost Ratio (BCR) values were generally as good or even better for MF treatment and treatments involving CP1 at both on station and on farm, compared to Ck. Although applying mineral fertilizer (MF) alone as currently done by many farmers appears to make economic sense, this practice is unlikely to be sustainable in the long term. Applying TP1_200 and TP1_300 are two possible strategies that are affordable to farmers and provide returns on investment at least as good as the current practice of sole application of MF. However, a long-term study to assess the effect of compost-activated biochar on crop productivity and soil quality is advised.

Impacted Application of Water-Hyacinth-Derived Biochar and Organic Manures on Soil Properties and Barley Growth

The biochar application can improve the physiochemical properties of both sandy and clayey loam soils and is considered a potential adaptation tool toward climate change. Therefore, the current study is novel in combining water-hyacinth-derived biochar with organic manures as a suggested effective way of treating the soil with biochar under arid and semiarid conditions. Water hyacinth weeds were slow pyrolyzed at a temperature of 300 °C, which resulted in nonalkaline biochar with a pH value of 6.31, which is suitable for alkaline soils. A pot experiment was established to study the impact of the solo application of nonalkaline water-hyacinth-derived biochar (WHB) and its combined application with farmyard (WHB/FM) and poultry manure (WHB/PM) at a rate of 1.5 and 3%, respectively, on some chemical and physical properties of sandy and clay loam soils and some barley’s growth parameters. WHB, WHB/FM, and WHB/PM significantly affected the soil pH at different application rates (1.5 and 3%) in sandy soil. A considerable alteration in water-stable aggregates (WSA), dispersion ratio (DR), available water content (AWC), and cation ratio of soil structural stability (CROSS) index resulted from combining manures (FM and PM) with biochar better than the solo application of biochar. WHB/PM treatments had a superior effect in improving barley’s growth. Relative increases were by 37.3 and 11.0% in plant height and by 61.6 and 28.5% in the dry matter in sandy and clayey loam soils, respectively. Under the conditions of this study, we can conclude that treating the soil with WHB/PM at a rate of 1.5 and 3% is the most effective application. The current study may have a vital role in Egyptian agriculture sustainability by enhancing the soil characteristics of the old agricultural and the newly reclaimed lands.

Effects of Biochar and Manure Co-Application on Aggregate Stability and Pore Size Distribution of Vertisols

BACKGROUND

The combination of biochar and organic manure has substantial local impacts on soil properties, greenhouse gas emissions, and crop yield. However, the research on soil health or quality is still in its early stages. Four pot experiments were carried out: C (30 g biochar (kg soil)^-1), M (10 g manure (kg soil)^-1), CM (15 g biochar (kg soil)^-1 + 5 g manure (kg soil)^-1), and the control (without any amendments).

RESULTS

When compared to C and M treatments, the MWD of CM was reduced by 5.5% and increased by 4.9%, respectively, and the micropore volume (5-30 m) was increased by 17.6% and 89.6%. The structural equation model shows that soil structural parameters and physical properties regulate the distribution of micropores (5-30 μm) in amended soil.

CONCLUSION

Our studies discovered that biochar mixed with poultry manure had antagonistic and synergistic effects on soil aggregate stability and micropore volume in vertisol, respectively, and thus enhanced crop yield by 71.1%, which might be used as a technological model for farmers in China's Huang-Huai-Hai region to improve low- and medium-yielding soil and maintain soil health.

Dairy Manure Co-composting with Wood Biochar Plays a Critical Role in Meeting Global Methane Goals

Livestock are the largest source of anthropogenic methane (CH₄) emissions, and in intensive dairy systems, manure management can contribute half of livestock CH₄. Recent policies such as California's short-lived climate pollutant reduction law (SB 1383) and the Global Methane Pledge call for cuts to livestock CH₄ by 2030. However, investments in CH₄ reduction strategies are primarily aimed at liquid dairy manure, whereas stockpiled solids remain a large source of CH₄. Here, we measure the CH₄ and net greenhouse gas reduction potential of dairy manure biochar-composting, a novel manure management strategy, through a composting experiment and life-cycle analysis. We found that biochar-composting reduces CH₄ by 79%, compared to composting without biochar. In addition to reducing CH₄ during composting, we show that the added climate benefit from biochar production and application contributes to a substantially reduced life-cycle global warming potential for biochar-composting: -535 kg CO₂e Mg^-1 manure compared to -194 kg CO₂e Mg^-1 for composting and 102 kg CO₂e Mg^-1 for stockpiling. If biochar-composting replaces manure stockpiling and complements anaerobic digestion, California could meet SB 1383 with 132 less digesters. When scaled up globally, biochar-composting could mitigate 1.59 Tg CH₄ yr^-1 while doubling the climate change mitigation potential from dairy manure management.

Biochar-based compost: a bibliometric and visualization analysis

The co-application of biochar compost as organic amendment for crop production and soil remediation has gained momentum due to their positive effect on plant growth and soil quality improvement. The application of biochar and compost which are green and cost-effective soil remediators would promote the availability and distribution of food, planetary conservation, alleviate poverty, and enhance the attainment of Sustainable Millennium Development Goals (SDGs). A bibliometric analysis was conducted to overview research on biochar compost from 2011 to 2021. Two hundred and fifty-four research papers were retrieved from the Scopus database and analyzed using VOS viewer. Analysis revealed that 217 (85.43%) were articles, 21 (8.27%) were conference papers, and 12 (4.72%) were review papers. The results showed an exponential increase in the number of publications. The most productive countries in the investigated subject were China (49), followed by USA (36), Australia (29), Italy (28), Germany (25), and Indonesia (20). After the search terms, 'soil,' which had links with keywords like 'soil fertility,' 'soil quality,' 'soil pollution,' 'phosphorus,' 'nitrogen,' 'maize,' 'greenhouse gas,' etc., had the highest occurrences (94). From the results of the current hotspot research in the field, the effect of biochar-compost mixture and co-composted biochar on soil remediation is currently being studied by several researchers. Biochar and compost incorporation in soil reduce the uptake of pollutants by plants which consequently increase essential nutrients for plant and soil productivity.

Superphosphate, biochar, and a microbial inoculum regulate phytotoxicity and humification during chicken manure composting

The germination index (GI) is the best index for evaluating compost phytotoxicity and maturity. In order to improve GI and reduce phytotoxicity of chicken manure compost, superphosphate, biochar, and a microbial inoculum were added in this study. Maturity indices (pH, electrical conductivity, and GI), water-soluble ion, organic matter, humic acid, humic precursor contents, and the bacteria community were analyzed during the experiment. NH₄⁺, volatile fatty acids, and humic acid strongly affected the GI, which increased as the humic acid content increased and the volatile fatty acid and NH₄⁺ contents decreased. The three additives affected compost maturity differently. Adding biochar decreased microbial diversity and complexity, but improved the GI mainly by affecting abiotic factors. Adding the microbial inoculum increased biotic activity and promoted humus and precursor formation. Superphosphate activated core functional bacteria and increased bacterial diversity and complexity, and 16 genera and 2 phyla (Gemmatimonadota and Chloroflexi) were found only in this composting pile. Superphosphate markedly accelerated humification and decreased the salt (NH₄⁺ and NO₃^-) and heavy metal ion (Cu²⁺, Cd²⁺, Cr³⁺) contents, forming stable substances to reduce the key phytotoxic matters, which in turn decreased the compost phytotoxicity and improved the GI. These results provide a new sight for promoting maturity by functional material regulation in composting.

Revamping highly weathered soils in the tropics with biochar application: What we know and what is needed

Fast weathering of parent materials and rapid mineralization of organic matter because of prevalent climatic conditions, and subsequent development of acidity and loss/exhaustion of nutrient elements due to intensive agricultural practices have resulted in the degradation of soil fertility and productivity in the vast tropical areas of the world. There is an urgent need for rejuvenation of weathered tropical soils to improve crop productivity and sustainability. For this purpose, biochar has been found to be more effective than other organic soil amendments due to biochar's stability in soil, and thus can extend the benefits over long duration. This review synthesizes information concerning the present status of biochar application in highly weathered tropical soils highlighting promising application strategies for improving resource use efficiency in terms of economic feasibility. In this respect, biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils. This paper identifies several advance strategies that can maximize the effectiveness of biochar application in weathered tropical soils. However, strategies for the reduction of costs of biochar production and application to increase the material's use efficiency need future development. At the same time, policy decision by linking economic benefits with social and environmental issues is necessary for successful implementation of biochar technology in weathered tropical soils. This review recommends that advanced biochar strategies hold potential for sustaining soil quality and agricultural productivity in tropical soils.

Impacts of gasification biochar and its particle size on the thermal behavior of organic waste co-composting process

This work investigates the effects of gasification biochar on the thermal behavior of organic municipal waste composting. Two different biochar granulometries were mixed in a 3% w/w share with the organic fraction of municipal waste and tested in nine (three per thesis and three as control) reactors of 1 m³ of volume, designed to simulate full-scale aerated static piles. The temperatures of each composter were monitored for 31 days of the active composting phase and used as key parameters for air flow tuning. After the active phase was completed, the air was turned off and the temperatures were monitored for an additional 31 days during compost maturation. Results show that biochar-aided composters run 4 °C hotter and are more stable in temperature compared to the control thesis. Experimental data were used as a basis for thermal energy modeling: the addition of fine biochar to composting material increased the thermal energy production by 0.5 MJ kg^-1 compared to the control thesis; coarse biochar increased the thermal energy production by 0.4 MJ kg^-1. The standard composting process, without biochar, produced 2.5 MJ kg^-1. Results might serve as a starting point for further considerations in terms of composting time reduction, improvement of the final product and reduction of process related issues, such as undesired anaerobic decomposition, leachate production and temperature instability.

Behavioral intentions of rural farmers to recycle human excreta in agriculture

Considerable progress has been made in developing human excreta recovery pathways and processes for maximum nutrient recovery and contaminant elimination. The demand segment has often been ignored as an area for future research, especially during the technology development. The findings from the few published articles on social acceptance show missing and inconclusive influence of demographic, sociological, and economic farmer-characteristics. This study endeavours to close this gap by using the social psychological theories, technology adoption theories and the new ecological paradigm to investigate the factors that influence the behavioral intentions of rural farmers to recycle human excreta in agriculture. Study findings show that social acceptance was driven by awareness, religiosity, income, source of income, and environmental dispositions. Perceived behavioral control represents a potential barrier to human excreta reuse. The study recommends the demographic, cultural, sociological, and economic mainstreaming of dissemination strategies of circular bioeconomy approaches within the context of agricultural innovation systems.

Biochar and nitrogen fertilizer co-application changed SOC content and fraction composition in Huang-Huai-Hai plain, China

Biochar can significantly enhance soil organic carbon (SOC) and crop yield, and it is therefore the preferred material for soil improvement in medium-low yield fields. In this study, a field experiment was designed to explore the impacts of biochar application on SOC content and fraction composition. Results indicated that incorporation of biochar into soil increased the SOC content by 26.9%-65.3% in the surface layer (0-10 cm) and 30.3%-63.0% in the subsurface layer (10-20 cm) of soil, while water-soluble organic carbon (WSOC) of the two layers was increased by 2.2-40.0% and 2.3-39.8%, respectively. Microbial biomass carbon decreased under conventional nitrogen treatments and increased with biochar addition under increased nitrogen application. The C:N value increased with biochar application, while the water-soluble C:N value of soil applied with 30 t ha^-1 biochar was lower than that of soil applied with 15 t ha^-1 biochar, both in the two tested soil layers. Wheat yield is evidently correlated with SOC, with the correlation coefficients of 0.919 and 0.952 in the surface and subsurface soil layers (P < 0.01), respectively. Particularly, increasing fulvic and humic acid-like compounds of WSOC promoted the bioavailability of nutrient elements, thereby increasing the crop yields. Therefore, biochar application is an effective means to fertilize middle-low yield soils through increasing SOC sequestration and nutrient reserves, or adjusting soil C:N value to a proper range, thereby reducing nutrient loss and increasing wheat yield.

Cadmium contamination in agricultural soils of Bangladesh and management by application of organic amendments: evaluation of field assessment and pot experiments

In recent years, cadmium (Cd) contamination in agricultural soils and its subsequent transfer to crops is one of the high-priority environmental and public health issues of global concern, especially in densely populated developing countries like Bangladesh. However, no effective strategy has been introduced or implemented yet to manage Cd-contaminated soils in order to sustain agricultural production with no human health risks. In this study, agricultural soil samples were collected from 60 locations of 10 upazilas from Tangail district to assess the extent of soil Cd contamination. The Cd concentration ranged from 0.83 to 4.08 mg kg^-1 with a mean of 2.17 mg kg^-1 in topsoil (0-15 cm), and from 0.67 to 3.74 mg kg^-1 with a mean of 2.10 mg kg^-1 in subsoil (16-30 cm). The values of contamination factor (CF) indicated that all the sampling locations were found to be highly contaminated with Cd. Pot trials with the application of different doses of biochar and vermicompost in Cd-contaminated soil (0.8 mg kg^-1 Cd) revealed that integrated application of biochar (5 t ha^-1) and vermicompost (5 t ha^-1) was the best treatment that significantly (p < 0.05) reduced plant Cd concentration (72%) and increased the biomass of experimental crop, Red amaranth (Amaranthus cruentus). This combined treatment also significantly reduced the uptake of Cr (37%) when co-contamination was present. The study suggests the application of biochar (5 t ha^-1) in combination with vermicompost (5 t ha^-1) to reduce human health risk and increase crop production when the soil is loamy sand in texture.

Mitigation of carbon and nitrogen losses during pig manure composting: A meta-analysis

Composting is a reliable way to recycle manure for use on croplands in sustainable agriculture. Poor management of the composting process can result in a decrease in the final compost quality and negative environmental impacts. Optimization technologies during composting have varied effects on the mitigation of carbon (C) and nitrogen (N) losses. To determine the feasibility and effectiveness of mitigation options, a meta-analysis was performed based on 68 studies in which C and/or N losses were investigated during pig manure composting. The results indicated that 48.7% of the total C (TC) was lost with 34.8% as CO₂-C and 0.9% as CH₄-C, and 27.5% of the total N (TN) was lost with 17.1% as NH₃-N and 1.5% as N₂O-N. The composting method and bulking agent type obviously influenced the C and N losses. CO₂-C and CH₄-C emission was significantly influenced by the initial C/N ratio and moisture, respectively. At the same time, NH₃-N and N₂O-N emissions were remarkably affected by the initial pH and composting duration, respectively. The results of the meta-analysis showed that TC and TN losses were reduced by 12.4% and 27.5%, respectively. Controlling feedstock, including the C/N ratio and moisture, could be regarded as N conservation technology. Controlling aeration, including turning frequency and ventilation rate, would be reliable in reducing greenhouse gas emissions. Applying additives, especially biochar and superphosphate, was found to be an effective method for synergistically mitigating C and N losses. Therefore, the production of high-quality compost products and minimization of environmental pollution will be achieved by a combination of adjusting the initial substrate properties, controlling the composting process conditions and applying additives.

Role of biochar, compost and plant growth promoting rhizobacteria in the management of tomato early blight disease

The individual role of biochar, compost and PGPR has been widely studied in increasing the productivity of plants by inducing resistance against phyto-pathogens. However, the knowledge on combined effect of biochar and PGPR on plant health and management of foliar pathogens is still at juvenile stage. The effect of green waste biochar (GWB) and wood biochar (WB), together with compost (Comp) and plant growth promoting rhizobacteria (PGPR; Bacillus subtilis) was examined on tomato (Solanum lycopersicum L.) physiology and Alternaria solani development both in vivo and in vitro. Tomato plants were raised in potting mixture modified with only compost (Comp) at application rate of 20% (v/v), and along with WB and GWB at application rate of 3 and 6% (v/v), each separately, in combination with or without B. subtilis. In comparison with WB amended soil substrate, percentage disease index was significantly reduced in GWB amended treatments (Comp + 6%GWB and Comp + 3%GWB; 48.21 and 35.6%, respectively). Whereas, in the presence of B. subtilis disease suppression was also maximum (up to 80%) in the substrate containing GWB. Tomato plant growth and physiological parameters were significantly higher in treatment containing GWB (6%) alone as well as in combination with PGPR. Alternaria solani mycelial growth inhibition was less than 50% in comp, WB and GWB amended growth media, whereas B. subtilis induced maximum inhibition (55.75%). Conclusively, the variable impact of WB, GWB and subsequently their concentrations in the soil substrate was evident on early blight development and plant physiology. To our knowledge, this is the first report implying biochar in synergism with PGPR to hinder the early blight development in tomatoes.

Biochar and effective microorganisms promote Sesbania cannabina growth and soil quality in the coastal saline-alkali soil of the Yellow River Delta, China

Soil salinization and nutrient deficiency have emerged as the major factors negatively impacting soil quality and primary productivity in the coastal saline-alkali soil of the Yellow River Delta. Biochar has been proposed as an efficient strategy for promoting plant growth and restoring degraded saline-alkali soil. However, knowledge is inadequate regarding the effects of adding Spartina alterniflora-derived biochar alone or in combination with effective microorganisms (EM) on the growth of Sesbania cannabina and soil quality in saline-alkali soil. To enhance this knowledge, a pot experiment with different EM treatments (without EM addition, EM-; with EM addition, EM+) and a gradient of biochar treatments (0%, B₀; 0.5%, B₁; 1.5%, B₂; and 3%, B₃; biochar weight/soil weight) was conducted. Our results showed that biochar addition alone and in combination with EM significantly increased seed germination, plant height, stem diameter, total biomass and plant nutrient uptake of S. cannabina. Biochar addition, EM addition and their interaction significantly decreased soil salt content efficiently and increased soil total carbon (TC), total nitrogen (TN), available phosphorus (AP) and available potassium (AK) but had little effect on soil pH. Biochar addition increased soil organic carbon, soil NH₄⁺ and NO₃-, microbial biomass carbon, and soil enzyme activities and these effects increased in strength when biochar and EM were present simultaneously. Of the treatments, the EM + B₃ treatment had the largest effects in terms of inhibiting salinization, increasing soil fertility, elevating soil nutrients and enzyme activities, and improving plant growth. Moreover, the application of biochar and EM promoted the growth of S. cannabina by enhancing plant nutrient uptake, improving soil fertility (e.g., TN, AP, AK, NH₄⁺ and NO₃^-), and elevating soil enzyme activities (urease and alkaline phosphatase activity). Overall, the integrated use of an appropriate biochar rate (3%) and EM for coastal saline-alkali soil could be an effective strategy to ameliorate soil salinity, improve soil quality and promote plant productivity.

The roles of co-composted biochar (COMBI) in improving soil quality, crop productivity, and toxic metal amelioration

The use of co-composted biochar (COMBI) made by the addition of biochar at the beginning of the composting process has greatly increased in agriculture during the last decade. There are more benefits of using the co-composting end product COMBI than using compost and biochar separately or the mixture of the two products. We conducted an extensive review of the production of several COMBIs and their contribution to the composting process and biochar properties as well as the further use of COMBIs in agricultural lands to improve soil health and increase crop yields, and to remediate areas severely contaminated with potentially toxic metals (PTMs). Although the number of researches focused on COMBI production and its application is so far limited, there is enough evidence to elucidate the importance of creating such products to promote sustainable agriculture and environmental safety. Even if a few drawbacks or side effects are found, they are outweighed by the many benefits achieved with COMBIs production and application in comparison to other amendments. The quality of both biochar and compost is largely improved in so many ways during the co-composting process, which in turn improved soil health and crop yields of up to 300% in some particular cases. This work improved the overall understanding of COMBI production and application in agriculture. Based on the review, we suggested future researches to better understand the mechanisms of COMBI long-term application to promote awareness on its role over time through alterations in its surface chemistry, ionic nutrient adsorption, supply (aging effect), and environmental implications.

A review of recent advancements in utilization of biomass and industrial wastes into engineered biochar

For past few years, biochar has gained a great deal of attention for its versatile utility in agricultural and environmental applications. The diverse functionality and environmental-friendly nature of biochar have motivated many researchers to delve into biochar researches and spurred rapid expansion of literature in recent years. Biochar can be produced from virtually all the biomass, but the properties of biochar are highly dependent upon the types of feedstock biomass and preparation methods. The overall performances of as-prepared biochar in treating soil and water contaminants is generally inferior to activated carbon due to its lower surface area and limited functionalities. This limitation has led to many follow-up studies that focused on improving material characteristics by imparting desired functionality. Such efforts have greatly advanced knowledge to produce better-performing engineered biochar with enhanced capability and versatility. To this end, this review was prepared to compile recent advancements in fabrication and application of engineered biochar, especially with respect to the influences of biomass feedstock on the properties of biochar and the utilization of industrial wastes in fabrication of engineered biochar.

Investigations of the effect of the amount of biochar on soil porosity and aggregation and crop yields on fertilized black soil in northern China

The combination of chemical fertilizer and biochar is regarded as a useful soil supplement for improving the properties of soil and crop yields, and this study describes how the biochar of maize straw can be used to improve the quality of the degraded black soil. This has been achieved by examining the effects of combining different amounts of biochar with chemical fertilizer on the porosities and aggregate formation of soil and exploring how these changes positively impact on crop yields. A field trial design combining different amounts of maize straw biochar [0 (NPK), 15.75 (BC1), 31.5 (BC2), and 47.25 t ha-1 (BC3)] with a chemical fertilizer (NPK) has been used to investigate changes in the formation of soil aggregate, clay content, soil organic carbon (SOC), and crop yields in Chinese black soil over a three year period from 2013 to 2015. The results of this study show that the addition of fertilizer and biochar in 2013 to black soil results in an increased soybean and maize yields from 2013 to 2015 for all the treatments, with BC1/BC2 affording improved crop yields in 2015, while BC3 gave a lower soybean yield in 2015. Total porosities and pore volumes were increased for BC1 and BC2 treatments but relatively decreased for BC3, which could be attributed to increased soil capillary caused by the presence of higher numbers of fine soil particles. The addition of biochar had a positive influence on the numbers and mean weight diameters (MWD) of soil macroaggregates (>0.25 mm) that were present, with the ratio of SOC to TN in soil macroaggregates found to be greater than in the microaggregates. The most significant amount of carbon present in macroaggregates (>2 mm and 0.25-2 mm) was observed when BC2 was applied as a soil additive. Increasing the levels of maze straw biochar to 47.25 t ha-1 led to an increase in the total organic carbon of soil, however, the overall amount of macroaggregates and MWD were decreased, which is possibly due to localized changes in microbial habitat. The supplementation of biochar increased in the amount of aromatic C present (most significant effect observed for BC2), with the ratio of aliphatic C to aromatic C found to be enhanced due to a relative reduction in the aliphatic C content with >2 mm particle fraction. These changes in organic carbon content and soil stability were analyzed using univariate quadratic equations to explain the relationship between the type of functional groups (polysaccharide C, aliphatic C, aromatic C, aliphatic C/aromatic C) present in the soil aggregates and their MWDs, which were found to vary significantly. Overall, the results of this study indicate that the use of controlled amounts of maize-straw biochar in black soil is beneficial for improving crop yields and levels of soil aggregation, however, the use of excessive amounts of biochar results in unfavorable aggregate formation which negatively impacts the yields of crop growth. The data produced suggest that aromatic C content can be used as a single independent variable to characterize the stability of soil aggregate when biochar/fertilizer mixtures are used as soil additives to boost growth yields. Analysis of soil and crop performance in black soil revealed that the application of maize-straw biochar at a rate of 15.75 and 31.5 t ha-1 had positive effects on crop yields, soil aggregation and accumulation of aromatic C in the aggregate fractions when a soybean-maize rotation system was followed over three years.

The Effects of Fertilizer Type and Application Time on Soil Properties, Plant Traits, Yield and Quality of Tomato

Compost is considered to be superior fertilizer for soil quality and productivity, and is commonly used with chemical fertilizer. The optimal mixed ratio of compost with chemical fertilizer and the best application time is necessary to know for sustainable agriculture practices and management. Compared to the control treatment, this study comprehensively evaluated the effects of four mixed ratios of compost with chemical fertilizer, two nitrogen application times of chemical fertilizer, and their interaction on the soil properties, plant traits, yield, and quality of tomato plants. The soil properties, plant traits, and yield of tomato with all compost-mixed fertilizers performed better than the treatment without fertilizer. Furthermore, the amounts of available nitrogen, phosphorus, organic matter, plant weight, and yield in a 30% chemical fertilizer + 70% compost treatments (CF30) were even better than those with pure chemical fertilizer (CF100). No significant effect of nitrogen application time and its interaction with the mixed ratio treatment was detected, and the quality of fruit remained consistent among treatments. This study demonstrated a suitable practical application method for cow manure compost as a nutrient source in tomato crop production under silty loam soil.

Can biochar reclaim coal mine spoil?

Surface coal mining activities completely destroy vegetation cover, soil and biodiversity. The aftermaths include huge coal mine spoil dumps, changed topography, drainage and landscape, deteriorated aesthetics and increased pollution load. These coal mine spoils are characterised by high rock fragments, extremely low water holding capacity, compacted and high bulk density, lack of organic carbon and plant nutrients, low cation exchange capacity, acidic pH and toxic metal contamination, which poses difficulties in reclamation. An array of studies has been focused on the sustainable use of biochar for restoration of degraded agricultural soil by improving the soil physicochemical, nutritional and biological properties. Although a volume of studies has been done on biochar application, its specialised application in reclamation of coal mine spoils is still atypical, also a systematic review on the mechanism by which biochar amends the mine spoil is lacking. This review focuses on i) factors affecting the biochar properties, ii) the mechanism involved in altering the physical, chemical and biological properties by biochar, (iii) remediation of potentially toxic elements in soil and restoration of degraded land using biochar, and, iv) highlighting the important aspects to be considered while using biochar for reclamation of coal mine spoil. Biochar prepared at 450 °C from a lignocellulosic rich biomass can be an alternative for reclamation for coal mine spoil. Review also suggested suitable methodologies for bulk production, application and economics of biochar in coal mine spoil reclamation.

Recent advances in biochar application for water and wastewater treatment: a review

In the past decade, researchers have carried out a massive amount of research on the application of biochar for contaminants removal from aqueous solutions. As an emerging sorbent with great potential, biochar has shown significant advantages such as the broad sources of feedstocks, easy preparation process, and favorable surface and structural properties. This review provides an overview of recent advances in biochar application in water and wastewater treatment, including a brief discussion of the involved sorption mechanisms of contaminants removal, as well as the biochar modification methods. Furthermore, environmental concerns of biochar that need to be paid attention to and future research directions are put forward to promote the further application of biochar in practical water and wastewater treatment.

Application of co-composted biochar significantly improved plant-growth relevant physical/chemical properties of a metal contaminated soil

A woody-biochar was added to waste biomass during a composting process. The resulting compost-char was amended to a metal contaminated soil and two plant species, L. perenne and E. sativa, were grown in a pot experiment to determine 1) plant survival and stress factors, 2) uptake of metals to plants and, 3) chemical characteristics of sampled soils and pore waters. Compost supplemented with biochar after the composting process were also tested, as well as a commercially available compost, for comparison. Co-composting with biochar hastened the composting process, resulting in a composite material of reduced odour, increased maturity, circum-neutral pH and increased moisture retention than compost (increase by 3% of easily removable water content). When amended to the soil, CaCl₂ extractable and pore water metals s were reduced by all compost treatments with little influence of biochar addition at any tested dose. Plant growth success was promoted furthest by the addition of co-composted biochar to the test soil, especially in the case of E. sativa. For both tested plant species significant reductions in plant metal concentrations (e.g. 8-times for Zn) were achieved, against the control soil, by compost, regardless of biochar addition. The results of this study demonstrate that the addition of biochar into the composting process can hasten the stability of the resulting compost-char, with more favourable characteristics as a soil amendment/improver than compost alone. This appears achievable whilst also maintaining the provision of available nutrients to soils and the reduction of metal mobility, and improved conditions for plant establishment.

Potentials, Limitations, Co-Benefits, and Trade-Offs of Biochar Applications to Soils for Climate Change Mitigation

Biochar is one of the most affordable negative emission technologies (NET) at hand for future large-scale deployment of carbon dioxide removal (CDR), which is typically found essential to stabilizing global temperature rise at relatively low levels. Biochar has also attracted attention as a soil amendment capable of improving yield and soil quality and of reducing soil greenhouse gas (GHG) emissions. In this work, we review the literature on biochar production potential and its effects on climate, food security, ecosystems, and toxicity. We identify three key factors that are largely affecting the environmental performance of biochar application to agricultural soils: (1) production condition during pyrolysis, (2) soil conditions and background climate, and (3) field management of biochar. Biochar production using only forest or crop residues can achieve up to 10% of the required CDR for 1.5 ∘ C pathways and about 25% for 2 ∘ C pathways; the consideration of dedicated crops as biochar feedstocks increases the CDR potential up to 15–35% and 35–50%, respectively. A quantitative review of life-cycle assessment (LCA) studies of biochar systems shows that the total climate change assessment of biochar ranges between a net emission of 0.04 tCO 2 eq and a net reduction of 1.67 tCO 2 eq per tonnes feedstock. The wide range of values is due to different assumptions in the LCA studies, such as type of feedstock, biochar stability in soils, soil emissions, substitution effects, and methodological issues. Potential trade-offs between climate mitigation and other environmental impact categories include particulate matter, acidification, and eutrophication and mostly depend on the background energy system considered and on whether residues or dedicated feedstocks are used for biochar production. Overall, our review finds that biochar in soils presents relatively low risks in terms of negative environmental impacts and can improve soil quality and that decisions regarding feedstock mix and pyrolysis conditions can be optimized to maximize climate benefits and to reduce trade-offs under different soil conditions. However, more knowledge on the fate of biochar in freshwater systems and as black carbon emissions is required, as they represent potential negative consequences for climate and toxicity. Biochar systems also interact with the climate through many complex mechanisms (i.e., surface albedo, black carbon emissions from soils, etc.) or with water bodies through leaching of nutrients. These effects are complex and the lack of simplified metrics and approaches prevents their routine inclusion in environmental assessment studies. Specific emission factors produced from more sophisticated climate and ecosystem models are instrumental to increasing the resolution and accuracy of environmental sustainability analysis of biochar systems and can ultimately improve the characterization of the heterogeneities of varying local conditions and combinations of type feedstock, conversion process, soil conditions, and application practice.