Is biochar-manure co-compost a better solution for soil health improvement and N2O emissions mitigation?

NH3 and greenhouse gas emissions during co-composting of lignite and poultry wastes and the following amendment of co-composted products in soil

Ammonia (NH3) and greenhouse gas (GHG) emissions are substantial contributors to C and N loss in composting. Lignite can increase N retention by absorbing N H 4 + and NH3. However, the effects of co-composting on NH3 and GHG emissions in view of closing nutrient cycle are still poorly investigated. In the study, poultry litter was composted without (CK) or with lignite (T1) or dewatered lignite (T2), and their respective composts N H 4 + Com_CK, Com_T1, and Com_T2) were tested in a soil incubation to assess NH3 and GHG emission during composting and following soil utilization. The cumulative NH3 flux in T1 and T2 were reduced by 39.3% and 50.2%, while N2O emissions were increased by 7.5 and 15.6 times, relative to CK. The total GHG emission in T2 was reduced by 16.8% compared to CK. Lignite addition significantly increased nitrification and denitrification as evidenced by the increased abundances of amoA, amoB, nirK, and nirS. The increased reduction on NH3 emission by dewatered lignite could be attributed to reduced pH and enhanced cation exchangeable capacity than lignite. The increased N2O was related to enhanced nitrification and denitrification. In the soil incubation experiment, compost addition reduced NH3 emission by 72%∼83% while increased emissions of CO2 and N2O by 306%∼740% and 208%∼454%, compared with urea. Com_T2 strongly reduced NH3 and GHG emissions after soil amendment compared to Com_CK. Overall, dewatered lignite, as an effective additive, exhibits great potential to simultaneously mitigate NH3 and GHG secondary pollution during composting and subsequent utilization of manure composts.

A comprehensive review on the preparation of biochar from digestate sources and its application in environmental pollution remediation

The preparation of biochar from digestate is one of the effective ways to achieve the safe disposal and resource utilization of digestate. Nevertheless, up to now, a comprehensive review encompassing the factors influencing anaerobic digestate-derived biochar production and its applications is scarce in the literature. Therefore, to fill this gap, the present work first outlined the research hotspots of digestate in the last decade using bibliometric statistical analysis with the help of VOSviewer. Then, the characteristics of the different sources of digestate were summarized. Furthermore, the influencing factors of biochar preparation from digestate and the modification methods of digestate-derived biochar and associated mechanisms were analyzed. Notably, a comprehensive synthesis of anaerobic digestate-derived biochar applications is provided, encompassing enhanced anaerobic digestion, heavy metal remediation, aerobic composting, antibiotic/antibiotic resistance gene removal, and phosphorus recovery from digestate liquor. The economic and environmental impacts of digestate-derived biochar were also analyzed. Finally, the development prospect and challenges of using biochar from digestate to combat environmental pollution are foreseen. The aim is to not only address digestate management challenges at the source but also offer a novel path for the resourceful utilization of digestate.

Malonic acid shapes bacterial community dynamics in compost to promote carbon sequestration and humic substance synthesis

The incorporation of malonic acid (MA) into compost as a regulator of the tricarboxylic acid (TCA) cycle has the potential to increase carbon sequestration. However, the influence of MA on the transformation of the microbial community during the composting process remains unclear. In this investigation, MA was introduced at different stages of chicken manure (CM) composting to characterize the bacterial community within the compost using high-throughput sequencing. We assess the extent of increased carbon sequestration by comparing the concentration of total organic carbon (TOC). At the same time, this study examines whether increased carbon sequestration contributes to humus formation, which was elucidated by evaluating the content and composition of humus. Our results show that the addition of MA significantly improved carbon sequestration within the compost, reducing the carbon loss rate (C loss (%)) from 64.70% to 52.94%, while increasing HS content and stability. High throughput sequencing and Random Forest (RF) analysis show that the introduction of MA leads to a reduction in the diversity of the bacterial communities, but enhanced the ability of bacterial communities to synthesize humus. Furthermore, the addition of MA favors the proliferation of Firmicutes. Also, the hub of operational taxonomic units (OTUs) within the community co-occurrence network shifts from Proteobacteria to Firmicutes. Remarkably, our study finds a significant decrease in negative correlations between bacteria, potentially mitigating substrate consumption due to negative interactions such as competition. This phenomenon contributes to the improved retention of TOC in the compost. This research provides new insights into the mechanisms by which MA regulates bacterial communities in compost, and provides a valuable theoretical basis for the adoption of this innovative composting strategy.

Response of soil N2O production pathways to biochar amendment and its isotope discrimination methods

Reducing nitrous oxide (N2O) emission from farmland is crucial for alleviating global warming since agriculture is an important contributor of atmospheric N2O. Returning biochar to agricultural fields is an important measure to mitigate soil N2O emissions. Accurately quantifying the effect of biochar on the process of N2O production and its driving factors is critical for achieving N2O emission mitigation. Recently, stable isotope techniques such as isotope labeling, natural abundance, and site preference (SP) value, have been widely used to distinguish N2O production pathways. However, the different isotope methods have certain limitations in distinguishing N2O production in biochar-amended soils where it is difficult to identify the relative contribution of individual pathways for N2O production. This paper systematically reviews the pathways of soil N2O production (nitrification, nitrifier denitrification, bacterial denitrification, fungal denitrification, coupled nitrification-denitrification, dissimilatory nitrate reduction to ammonium and abiotic processes) and their response mechanism to the addition of biochar, as well as the development history and advantages of isotopes in differentiating N2O production pathways in biochar-amended soils. Moreover, the limitations of current research methods and future research directions are proposed. These results will help resolve how biochar affects different processes that lead to soil N2O generation and provide a scientific basis for sustainable agricultural carbon sequestration and the fulfilment of carbon neutrality goals.

Mechanisms of mitigating nitrous oxide emission during composting by biochar and calcium carbonate addition

To investigate the mechanisms underlying effects of biochar and calcium carbonate (CaCO3) addition on nitrous oxide (N2O) emissions during composting, this paper conducted a systematic study on mineral nitrogen (N), dissolved organic carbon (C) and N, sources of N2O, and functional genes. Biochar and CaCO3 addition decreased N2O emissions by 26.5-47.8% (9.5-96.9 mg N kg-1 dw) and 13.9-37.4% (12.0-121.0 mg N kg-1 dw) compared to the control (14.3-179.7 mg N kg-1 dw), respectively. The mitigation of N2O emission was caused by decreased contribution of ammonia-oxidizing bacteria (AOB) and fungi to N2O production due to diminished AOB amoA, fungal nirK and P450 gene abundances, or by stimulated N2O reduction to N2 owing to increased abundances of nosZⅠ and nosZⅠⅠ genes under biochar and CaCO3 addition. The findings suggest that the addition of biochar or CaCO3 is effective in mitigating N2O emission during composting.

Impact of bentonite on greenhouse gas emissions during pig manure composting and its subsequent application

Additives were widely investigated to retain the nutrients and mitigate the greenhouse gas emissions (GHGs) during manure composting. However, the sustained effects of additives on the GHGs emissions following incorporation of composts to soil were scarcely explored. This study evaluated the effects of bentonite added at the beginning of pig manure composting on the GHGs emissions during two successive processes, i.e., composting and soil incubation amended with composting products. Addition of bentonite did not hinder the composting process and alter the total CO2 emission. On the other hand, reduction by about 17% and 29% for CH4 and N2O emission, respectively, was achieved in the presence of bentonite during composting. Incorporation of the final composting products to soil enhanced significantly the soil C and N of various forms, and gas emissions of CO2 and N2O. However, no significant differences were observed between bentonite-manure co-compost and manure-only compost application except for the N2O emission. Compared to the manure-only compost, compost amended with bentonite reduced N2O loss by around 6.8%, but not statistically significant. This study confirmed that addition of bentonite at the composting stage can mitigate the GHGs emission considering both composting and compost application stages, with all reductions occurring at the composting stage.

Acidified biochar improves lead tolerance and enhances morphological and biochemical attributes of mint in saline soil

Lead (Pb) toxicity is a significant environmental issue, especially in areas with a past of industrial activities and mining. The existence of Pb in the soil can have negative impacts on plant growth and development, and it can also pose a risk to human health through the food chain. Acidified carbon has shown promise as an effective management technology for mitigating Pb toxicity. This study provides important insights into the potential of acidified biochar as a low-cost and eco-friendly method for managing Pb-contaminated soils. The current study explores the effectiveness of acidified biochar (AB) in alleviating Pb stress in mint. The study involved two levels of Pb (0 = control and 200 mg/kg Pb) and four levels of AB as treatments (0, 0.45, 0.90, and 1.20%). Results indicate that 1.20% AB was the most effective treatment, significantly decreasing root and shoot Pb concentration while enhancing shoot and root fresh and dry weight, shoot and root length, and shoot and root N, P, and K concentration. Moreover, a significant decrease in MDA (0.45AB, 0.90AB, and 1.20AB caused a decline in MDA content by 14.3%, 27.8%, and 40.2%, respectively) and an increase in ascorbic acid (0.45AB, 0.90AB, and 1.20AB led to an increase in ascorbic acid content of 1.9%, 24.8%, and 28.4%, respectively) validated the effectiveness of 1.20% AB compared to the control. Adding 0.45AB, 0.90AB, and 1.20AB led to an increase in soluble sugar content of 15.6%, 27.5%, and 32.1%, respectively, compared to the treatment without AB. Further investigations at the field level are suggested to confirm the efficacy of 1.20% AB as the best treatment against Pb toxicity in saline soil conditions.

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.

Can Biochar Improve the Sustainability of Animal Production?

Animal production is a significant contributor of organic and inorganic contaminants in air, soil, and water systems. These pollutants are present beginning in animal houses and impacts continue through manure storage, treatment, and land application. As the industry is expected to expand, there is still a lack of affordable, sustainable solutions to many environmental concerns in animal production. Biochar is a low-cost, sustainable biomaterial with many environmental remediation applications. Its physicochemical properties have been proven to provide environmental benefits via the adsorption of organic and inorganic contaminants, promote plant growth, improve soil quality, and provide a form of carbon sequestration. For these reasons, biochar has been researched regarding biochar production, and application methods to biological systems have a significant influence on the moisture content, pH, microbial communities, and carbon and nitrogen retention. There remain unanswered questions about how we can manipulate biochar via physical and chemical activation methods to enhance the performance for specific applications. This review article addresses the positive and negative impacts of biochar addition at various stages in animal production from feed intake to manure land application.

Co-composted biochar derived from rice straw and sugarcane bagasse improved soil properties, carbon balance, and zucchini growth in a sandy soil: A trial for enhancing the health of low fertile arid soils

Sustainable management of low fertile arid soils using carbon-rich organic amendments such as biochar and compost is of great concern from both agricultural and environmental points of view. The impact of pyrolysis, composting, and co-composting processes of different feedstocks on carbon loss and emissions, soil properties, and plant growth in arid soils with low organic matter content has not been sufficiently explored yet. Consequently, the aim of this work was to 1) investigate the effects of the pyrolysis, composting, and co-composting processes on the properties of the produced biochar, compost, and co-composted biochar from rice straw (RS) and sugarcane bagasse (SB), and 2) examine the impact of addition of RB biochar (RSB), SB biochar (SBB), RS compost (RSC), SB compost (SBC), co-composted RS biochar (RSCB), and co-composted SB biochar (SBCB) at an application dose of 10 ton/hectare on soil properties, carbon emission, and growth of zucchini (Cucurbita pepo) in a sandy arid soil. Carbon loss (kg C kg^-1 feedstock) was significantly (P < 0.05) lower during the preparation of the compost (90.36 in RSC, 220.00 in SBC) and co-composted-biochar (146.35 in RSCB, 125.20 in SBCB) than in biochar (176.5 in RSB, 305.6 in SBB). The C/N ratios of the compost and co-composted biochar (11-28.5) were narrower than the corresponding values of biochars (48-90). All amendments increased significantly soil organic carbon content (2.5 in RSC to 5.5 g kg^-1 in RSCB), as compared to the non-amended control (1.2 g kg^-1). All amendments, particularly RSCB, increased significantly (P < 0.05) the zucchini seed vigor index, dry weight, total chlorophyll content, and root and shoot length, as compared to the control. Moreover, RSCB was the only amendment that showed a positive soil carbon balance. The modified integrated two-way ecological model data also indicated that the co-composted biochar, particularly RSCB, is a promising amendment to improve soil quality and plant growth in sandy arid soils. However, those data should be verified under field conditions.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Biochar derived from spent mushroom substrate reduced N2O emissions with lower water content but increased CH4 emissions under flooded condition from fertilized soils in Camellia oleifera plantations

Agricultural soils are major sources of greenhouse gases (GHGs) that related with intensive fertilizer input. Biochar is widely used to mitigate GHGs, which may interact with soil water content impacting GHG emissions. Camellia oleifera fruit shell (FS) and spent mushroom substrate (MS) are ideal biochar feedstocks. However, the impact of water content and biochar on soil GHG emissions has not been thoroughly understood. Here, we examined CH₄ and N₂O emissions from C. oleifera plantation soils as affected by biochar (derived from MS or FS, 1 g 25 g^-1 soil), water content (60%, 120%, 240% or 360% water holding capacity, WHC), and fertilization (control or chicken manure, CM 2.5 g 25 g^-1 soil). We determined the abundance of related microbial functional genes to obtain the underlining mechanisms. The results showed that higher N₂O emissions occurred in soils with 120%WHC, due to increased abundance of AOA, AOB and nirS. MS or FS biochar differed in their effects on soil GHG emissions with different WHC. MS biochar was higher in pH, C/N and specific surface area, and mitigated more N₂O emissions from soils with CM and 120%WHC relative to FS biochar (by 92.9% and 34.6%, respectively). MS biochar significantly decreased abundance of nitrification related functional genes (AOA, AOB) in soils with 120%WHC and CM, which explained the decrease in N₂O emissions. However, MS biochar increased cumulative CH₄ emissions from flooded soils via increase in mcrA abundance. Thereby, biochar feedstocks should be considered in CH₄ and N₂O mitigations from soils with different water contents.

Effect of biochar amendment on compost quality, gaseous emissions and pathogen reduction during in-vessel composting of chicken manure

Because of rapid development in the livestock industry, the production of chicken manure has subsequently increased, which may contribute to environmental pollution. In this regard, in-vessel composting of biochar amended chicken manure and sawdust mixtures was investigated to find out the effect of biochar at the ratios of 0% (control), 3% (T1), 5% (T2), and 10% (T3) on ammonia and greenhouse gases (GHGs) emission, compost quality, pathogenic contaminants and phytotoxicity. The composting process was performed in 100-L, pilot-scale, plastic, cylindrical vessels for 50 days. The addition of biochar (3%, 5%, and 10%) increased the thermophilic temperature with a significant reduction in gaseous emissions (ammonia and CO₂), microbial pathogens (Escherichia coli and Salmonella sp.), and phytotoxicity (Lepidium sativum seed germination assay) compared with that of the control compost products. However, according to the obtained results with in-vessel composting, the amendment of 10% biochar showed the most significant effects concerning the quality of the compost nutrients. The study reveals that the addition of biochar during in-vessel chicken manure composting is beneficial in the reduction of gaseous emissions and pathogenic microorganisms apart from improvement in plant nutrients.

Proliferation of antibiotic-resistant microorganisms and associated genes during composting: An overview of the potential impacts on public health, management and future

Antibiotic residues together with non-antibiotic drugs and heavy metals act as a selective pressure for the spread of antibiotic-resistant microorganisms (ARMs), antibiotic-resistant genes (ARGs), and mobile genetic elements (MGEs) during composting of livestock manure. ARMs, ARGs and MGEs have become emerging contaminants since they are regularly implicated in the majority of compost produced from livestock manure. The prevalence of these contaminants in agricultural soil receiving compost has drawn huge attention globally due to the risks they pose to the total environment. Although a large body of literature exists on the application of composting methods in minimizing the relative abundance of these contaminants, there is a paucity of information on the robustness, limitations and opportunities and threats of various composting protocols currently deployed. To address this knowledge gap, the current review compiled literature on the origin and mechanisms of the proliferation of ARMs, ARGs, and MGEs during composting of livestock manure. The effectiveness of current composting protocols in the reduction or removal of emerging contaminants was evaluated. Furthermore, the potential environmental impacts and human health risks of these contaminants following land application of compost were also presented. Finally, we propose some strategic approaches for the reduction of ARGs and MGEs during composting of livestock manure.

Effects of Organic Fertilizers on the Soil Microorganisms Responsible for N2O Emissions: A Review

The use of organic fertilizers constitutes a sustainable strategy to recycle nutrients, increase soil carbon (C) stocks and mitigate climate change. Yet, this depends largely on balance between soil C sequestration and the emissions of the potent greenhouse gas nitrous oxide (N₂O). Organic fertilizers strongly influence the microbial processes leading to the release of N₂O. The magnitude and pattern of N₂O emissions are different from the emissions observed from inorganic fertilizers and difficult to predict, which hinders developing best management practices specific to organic fertilizers. Currently, we lack a comprehensive evaluation of the effects of OFs on the function and structure of the N cycling microbial communities. Focusing on animal manures, here we provide an overview of the effects of these organic fertilizers on the community structure and function of nitrifying and denitrifying microorganisms in upland soils. Unprocessed manure with high moisture, high available nitrogen (N) and C content can shift the structure of the microbial community, increasing the abundance and activity of nitrifying and denitrifying microorganisms. Processed manure, such as digestate, compost, vermicompost and biochar, can also stimulate nitrifying and denitrifying microorganisms, although the effects on the soil microbial community structure are different, and N₂O emissions are comparatively lower than raw manure. We propose a framework of best management practices to minimize the negative environmental impacts of organic fertilizers and maximize their benefits in improving soil health and sustaining food production systems. Long-term application of composted manure and the buildup of soil C stocks may contribute to N retention as microbial or stabilized organic N in the soil while increasing the abundance of denitrifying microorganisms and thus reduce the emissions of N₂O by favoring the completion of denitrification to produce dinitrogen gas. Future research using multi-omics approaches can be used to establish key biochemical pathways and microbial taxa responsible for N₂O production under organic fertilization.

Dynamics of soil N2O emissions and functional gene abundance in response to biochar application in the presence of earthworms

Nitrous oxide (N₂O) is a devastating greenhouse gas and acts as an ozone-depleting agent. Earthworms are a potential source of soil N₂O emissions. Application of biochar can mitigate earthworm-induced N₂O emissions. However, the underlying interactive mechanism between earthworms and biochar in soil N₂O emissions is still unclear. A 35-day laboratory experiment was conducted to examine the soil N₂O emission dynamics for four different treatments, earthworm presence with biochar application (EC), earthworm presence without biochar application (E), earthworm absence with biochar application (C) and earthworm absence without biochar application, and the control. Results indicated a negative impact of biochar on earthworm activity, displaying a significantly (p ≤ 0.05) lower survival rate and biomass of earthworms in treatment EC than E. Compared with the control, earthworm presence significantly (p ≤ 0.05) increased cumulative N₂O emissions, while application of biochar in the presence of earthworms significantly (p ≤ 0.05) decreased cumulative N₂O emissions (485 and 690 μg kg^-1 for treatments EC and E, respectively). Treatments E and EC significantly (p ≤ 0.05) increased soil microbial biomass carbon (MBC), ammonium (NH₄⁺-N), nitrate (NO₃^-N), and dissolved organic carbon (DOC) content and soil pH as compared with the control. The gene copy number of 16 S rRNA, AOA, AOB, nirS, and nosZ increased for all treatments when compared with the control; however, a significant (p ≤ 0.05) difference among the studied genes was only observed for the nosZ gene (2.05 and 2.56 × 10⁶ gene copies g^-1 soil for treatments E and EC, respectively). Earthworm-induced soil N₂O emissions were significantly (p ≤ 0.05) reduced by biochar addition. The possible underlying mechanisms may include: (1) short-term negative impacts on earthworm activity; (2) a change of functional gene abundance in earthworm casts; and (3) an increase in soil pH due to addition of biochar.

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.

Use of an in situ thermoelectric generator for electric field-assisted aerobic composting

Electric field-assisted aerobic composting (EAAC) is a simple and effective process. To further improve the EAAC process and make good use of waste heat during composting, in this study, we designed an in situ thermoelectric generator using thermoelectric sheets and applied it for EAAC. The findings show that the voltage generated was 8.8-18.6 V, and the maximum power was over 7 W. A direct current-to-direct current (DC-DC) voltage converter was used to stabilize the output at 6.0 V. Self-powered EAAC (sp-EAAC) enhanced compost maturity compared to conventional aerobic composting (CAC). The germination index reached 118% and 88% in sp-EAAC and CAC, respectively, at the end of composting. This work verified that the temperature gap between compost and the environment could be used for the EAAC process, opening a new way to recover waste heat during aerobic composting and accelerate compost maturity.

Efficiency of Wheat Straw Biochar in Combination with Compost and Biogas Slurry for Enhancing Nutritional Status and Productivity of Soil and Plant

In the present study, we investigated the impact of different combinations of wheat straw biochar, compost and biogas slurry on maize growth, physiology, and nutritional status in less productive soils. The experiment was performed as a completely randomized block design in a greenhouse pot experiment. The compost and biogas slurry were applied with and without biochar. The results revealed that a combination of biochar, compost, and biogas slurry enhanced the cation exchange capacity (31%), carbon (83%), phosphorus (67%) and potassium (81%) contents in the soil. Likewise, a significant increase in soil microbial biomass carbon (15%) and nitrogen (37%) was noticed with the combined use of all organic amendments. Moreover, the combined application of biochar, compost and biogas slurry enhanced soil urease and β-glucosidase activity up to 96% and 67% over control respectively. In addition, plant height, chlorophyll content, water use efficiency and 1000-grain weight were also enhanced up to 54%, 90%, 53% and 21% respectively, with the combined use of all amendments. Here, biochar addition helped to reduce the nutrient losses of compost and biogas slurry as well. It is concluded that biochar application in combination with compost and biogas slurry could be a more sustainable, environment-friendly and cost-effective approach, particularly for less fertile soils.

The mechanisms of biochar interactions with microorganisms in soil

Biochar, a carbonaceous material, is increasingly used in the remediation of the anthropogenically polluted soils and the restoration of their ecological functions. However, the interaction mechanisms among biochar, inorganic and organic soil properties and soil biota are still not very clear. The effect of biochar on soil microorganisms is very diverse. Several mechanisms of these interactions were suggested. However, a well acceptable mechanism of biochar effect on soil microorganisms is still missing. Therefore, efforts were made to examine and proposed a mechanism of the interactions between biochar and microorganisms, as well as existing problems of biochar impacts on main groups of soil enzymes, the composition of the microbiota and the detoxification (heavy metals) and degradation (polycyclic aromatic hydrocarbons) of soil pollutants. The data on the process of biochar colonization by microorganisms and the effect of volatile pyrolysis products released by biochar on the soil microbiota were analysed in detail. The effects of biochar on the physico-chemical properties of soils, the content of mineral nutrients and the response of microbial communities to these changes are also discussed. The information provided here may contribute to the solution of the feasibility, effectiveness and safety of the biochar questions to enhance the soil fertility and to detoxify pollutants in soils.

Effects of biochar particle size and concomitant nitrogen fertilization on soil microbial community structure during the maize seedling stage

Biochar is widely used as a soil amendment, either alone or in association with fertilizer. However, the effects of biochar particle size on the soil microbial community are largely unclear. Biochar was divided into two groups according to diameter sizes: < 1 mm and 2.5-5 mm (labeled as CB1 and CB5, respectively). A pot experiment was established in which maize (Zea maize L.) was treated with CB1, CB5, and/or external nitrogen (N, NH₄NO₃). At the end of the seedling period (45 days), analyses of soil microbial community structure and other soil and crop properties were conducted. The biochar (regardless of N addition) enhanced microbial biomass and activity. CB1 had a stronger capacity than CB5 to modify soil microbial community structure by promoting soil microbial groups (e.g., fungi, Gram-negative bacteria), which is likely due to CB1 undergoing a series of more intense processes (e.g., nutrient release, mineralization) than CB5. However, this difference was diminished or disappeared when N was added, mainly due to the masking effect of soil acidification that was induced by N fertilization. Collectively, fine biochar has a stronger effect on soil microbial community than coarse biochar. Particle size only affects soil microbial community structure when biochar is applied alone; it has no effect when biochar is applied in association with chemical N fertilizer, at least during the seedling period. The relationship between particle size and soil microbial community needs to be considered when using biochar for soil amendment.

Nitrification plays a key role in N2O emission in electric-field assisted aerobic composting

Nitrous oxide (N₂O) emission is a serious environmental problem in composting. Previous studies have indicated that electric field assistance results in lower N₂O emissions in aerobic composting; however, the exact mechanisms involved in electric-field assisted aerobic composting (EAAC) are not clear. In this study, the biological N transformation processes and the N-associated genes were investigated. The results demonstrated that electric field application inhibited nitrification, weakened the nitrifying functional genes (the hao and nxrA genes declined maximally by 86% and 86.8%, respectively), and increased the N₂O consumption-related gene (nosZ) by a maximum factor of 2.76 compared with that in CAC. The correlation analysis demonstrated that nitrification was the main source of N₂O emission in EAAC. The findings imply that EAAC is a promising process for mitigating N₂O emission at the source during aerobic composting.

The role of biochars in sustainable crop production and soil resiliency

Biochar is a promising soil additive for use in support of sustainable crop production. However, the high level of heterogeneity in biochar properties and the variations in soil composition present significant challenges to the successful uptake of biochar technologies in diverse agricultural soils. An improved understanding of the mechanisms that contribute to biochar-soil interactions is required to address issues related to climate change and cultivation practices. This review summarizes biochar modification approaches (physical, chemical, and biochar-based organic composites) and discusses the potential role of biochar in sustainable crop production and soil resiliency, including the degradation of soil organic matter, the improvement of soil quality, and reductions in greenhouse gas emissions. Biochar design is crucial to successful soil remediation, particularly with regard to issues arising from soil structure and composition related to crop production. Given the wide variety of feedstocks for biochar production and the resultant high surface heterogeneity, greater efforts are required to optimize biochar surface functionality and porosity through appropriate modifications. The design and establishment of these approaches and methods are essential for the future utilization of biochar as an effective soil additive to promote sustainable crop production.

Biochar suppresses N2O emissions and alters microbial communities in an acidic tea soil

Biochar has been considered as a promising soil amendment for improving fertility and mitigating N₂O emission from the arable land. However, biochar's effectiveness in acidic tea soil and underlying mechanisms are largely unknown. We conducted a short-term microcosm experiment using two biochars (1% w/w, LB, generated from legume and NLB, non-legume biomass, respectively) to investigate the effects of biochar amendments on soil chemical properties, N₂O emission, and microbial community in an acidic soil. Soil and headspace gas samples were taken on 1, 10, and 30 day's incubation. Biochar amendment increased soil pH and DOC, however, significantly reduced soil inorganic N. Both biochars at ~ 1% addition had little effect on microbial CO₂ respiration but suppressed soil N₂O emission by ~ 40% during the incubation. The divergence in N₂O efflux rates between soils with and without biochar addition aligned to some degree with changes in soil pH, inorganic N, and dissolved organic C (DOC). We also found that biochar addition significantly modified the fungal community structure, in particular the relative abundance of members of Ascomycota, but not the bacterial community. Furthermore, the copy number of nosZ, the gene encoding N₂O reductase, was significantly greater in biochar-amended soils than the soil alone. Our findings contribute to better understanding of the impact of biochar on the soil chemical properties, soil N₂O emission, and microbial community and the consequences of soil biochar amendment for improving the health of acidic tea soil.

Methane and Nitrous Oxide Flux after Biochar Application in Subtropical Acidic Paddy Soils under Tobacco-Rice Rotation

Biochar amendment is a good means of mitigating methane (CH₄) and nitrous oxide (N₂O) emissions. However, the effects of biochar amendment on N₂O and CH₄ reduction in soil under rotation with different soil moisture contents is not well understood. To understand CH₄ and N₂O flux from soil with biochar amendment under water-unsaturated and water-saturated conditions, a field experiment was conducted in a tobacco-rice rotation field in subtropical China to investigate N₂O and CH₄ emissions following soil amendment with tobacco straw biochar at rates of 0, 10, 40 and 80 t·ha⁻¹ (B0, B10, B40 and B80, respectively). N₂O and CH₄ emissions were monitored by a closed-chamber method in the water-unsaturated tobacco (UT) and water-saturated rice (SR) seasons during the 2015 planting season. The soil pH increased from 5.4 in the control to 6.1 in the soil amended with biochar at 80 t·ha⁻¹ in the UT season. During both the UT and SR seasons, with biochar amendment at 40 and 80 t·ha⁻¹, the soil bulk density (BD) decreased, while the soil organic matter (SOM) and available potassium (Av. K) contents increased. N₂O flux was significantly greater in UT than in SR in the controls but decreased with the application of biochar during both the UT and SR seasons. The cumulative CH₄ emission decreased with the rate of biochar application and the methanotroph pmoA gene copy number in soils and increased with the methanogenic archaea 16Sr DNA gene copy number in soils during the rice-cropping season. These results indicated that biochar amendment could decrease methanogenic archaea and increase of methanotroph pmoA gene, which are the mechanistic origin for CH₄ reduction.

Effects of combined biochar and organic fertilizer on nitrous oxide fluxes and the related nitrifier and denitrifier communities in a saline-alkali soil

This study intended to evaluate the combined effects of both biochar and organic fertilizer on nitrous oxide (N₂O) fluxes and composition of nitrifier and denitrifier of saline-alkali soil. Therefore, four different treatments such as CK (only chemical fertilizer), B (only biochar), M (only organic fertilizer), BM (B:M = 1:1) were used in this experiment. The results showed that N₂O emissions were decreased in B and BM treatments compare to the control. In contrast, N₂O emissions were highest before day 12 but lowest after day 19 in M treatment compare to the control. Application of biochar, organic fertilizer and biochar plus organic fertilizer decreased the nirS and nirK genes copies and enhanced the nosZ gene copies which resulting in the lower N₂O fluxes. The ammonia-oxidizing bacteria (AOB) amoA and nirK genes copies were significantly increased by organic fertilizer before day 12, leading to high N₂O emissions. The genera Nitrosospira (AOB) and Nitrososphaera (ammonia-oxidizing archaea, AOA) assumed absolute superiority. Additionally, Nitrosospira (AOB) was also appeared in nirK-type denitrifiers, illustrating denitrification was carried out by nitrifiers. The genera Azospirillum (nirS), Burkholderia (nosZ) and Polymorphum (nosZ) were dominant in CK. There was only one dominant genus, Mesorhizobium (nosZ) in the B treatment. The genera Mesorhizobium (nirK), Azoarcus (nirS), Kocuria (nirS) and Pseudomonas (nosZ) occupied the main status in the M treatment. The relative abundance of Rhodanobacter (nirS) and Azospirillum (nosZ) were higher in the BM treatment compared with other treatments. Soil water content (SWC), pH, NH₄⁺-N and NO₃^--N were the main factors affecting AOB and denitrifiers, which influencing N₂O emissions. Overall, combined application of biochar and organic fertilizer can reduce the N₂O emission where AOB and nirK-type denitrifier were the main contributors to the N₂O emission.

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

The combined use of biochar and compost as a soil amendment presents benefits to crops and nutrient cycling. Although there are literature reviews regarding biochar and biochar-compost mixtures, a quantitative literature review on the role of co-composted biochar (hereby called COMBI) in plant productivity is currently missing. The goal of this review paper is to find evidence-based measures of the effects of application rates, soil pH, plant types, biochar feedstock, and compost materials, on plant productivity. Plant productivity covers a variety of measurements but mostly refers to grain yield and above-ground biomass. Response ratio was selected as the effect size. Funnel plot showed that the studies were reasonably symmetrically distributed around the mean effect size. Results showed that application rates of <20 t/ha and >30 t/ha significantly increased plant productivity by 48.3 and 15.7%, respectively, while no significant yield increases were found for the application rates between 20 and 30 t/ha. When data was grouped based on the soil pH, the greatest increase in plant productivity was found to be at acidic soil pH values (pH 4-5), which was expected because the liming effect of biochar is often reported as one of the main mechanisms behind the increased crop yields. When different plant species were compared, cereal grasses grown with COMBI yielded significantly higher grain yields (39.7%). Rice husk biochar yielded the highest increase in productivity but this result was based on only one study. The second highest increase was obtained with wood-based biochars (29.4%) based on ten studies. The effect sizes found with our meta-analyses are based on 14 research works worldwide and represent the most updated information regarding the effects of COMBI on plant production. As more data on COMBI become available, data analyses can be updated to make more robust comparisons.

A Pine Enhanced Biochar Does Not Decrease Enteric CH4 Emissions, but Alters the Rumen Microbiota

The objective of this study was to examine the effect of a pine enhanced biochar (EB) on rumen fermentation, apparent total tract digestibility, methane (CH4) emissions, and the rumen and fecal microbiome of Angus × Hereford heifers fed a barley silage-based diet. The experiment was a replicated 4 × 4 Latin square using 8 ruminally cannulated heifers (565 ± 35 kg initial BW). The basal diet contained 60% barley silage, 35% barley grain and 5% mineral supplement with EB added at 0% (control), 0.5, 1.0, or 2.0% (DM basis). Each period lasted 28 days, consisting of 14 days adaptation and 14 days of measurements. Samples for profiling of the microbiome in rumen liquid, solids and feces were collected on d 15 before feeding. Rumen samples for fermentation characterization were taken at 0, 3, 6, and 12 h post feeding. Total collection of urine and feces was conducted from days 18 to 22. Heifers were housed in open-circuit respiratory chambers on days 26-28 to estimate CH4 emissions. Ruminal pH was recorded at 1-min intervals during CH4 measurements using indwelling pH loggers. Data were analyzed with the fixed effects of dietary treatment and random effects of square, heifer within square and period. Dry matter intake was similar across treatments (P = 0.21). Ammonia N concentration and protozoa counts responded quadratically (P = 0.01) to EB in which both were decreased by EB included at 0.5 and 1.0%, compared to the control and 2.0% EB. Minimum pH was increased (P = 0.04), and variation of pH was decreased (P = 0.03) by 2.0% EB. Total tract digestibility, N balance and CH4 production were not affected (P ≥ 0.17) by EB. Enhanced biochar decreased the relative abundance of Fibrobacter (P = 0.05) and Tenericutes (P = 0.01), and increased the relative abundance of Spirochaetaes (P = 0.01), Verrucomicrobia (P = 0.02), and Elusimicrobia (P = 0.02). Results suggest that at the examined concentrations, EB was ineffective at decreasing enteric CH4 emissions, but did alter specific rumen microbiota.

Electric field induces electron flow to simultaneously enhance the maturity of aerobic composting and mitigate greenhouse gas emissions

The long maturation period and greenhouse gas (GHG) emission are two major problems that arise during aerobic composting, mainly due to the low efficiency of O₂ transmission and utilization. In this study, a novel electric-field-assisted aerobic composting (EAC) process was tested by simply applying a direct-current voltage of 2 V to a conventional aerobic composting (CAC) process. Compared with the CAC process, the maturation time and the total GHG for the EAC process were reduced by 33% and 70%, respectively. Furthermore, the analyses of O₂ consumption and microbial communities demonstrated that the electric field had enhanced O₂ utilization by 30 ± 9% and increased the relative abundance of electroactive bacteria by about 3.4-fold compared to CAC. This work has represented a proof of principle for EAC and suggests that the electric field is an effective and environmentally friendly strategy for enhancing compost maturity and mitigating GHG emissions during aerobic composting.

Eighteen-Year Farming Management Moderately Shapes the Soil Microbial Community Structure but Promotes Habitat-Specific Taxa

Soil microbes have critical influence on the productivity and sustainability of agricultural ecosystems, yet the magnitude and direction to which management practices affect the soil microbial community remain unclear. This work aimed to examine the impacts of three farming systems, conventional grain cropping (CON), organic grain cropping (ORG), and grain cropping-pasture rotation (ICL), on the soil microbial community structure and putative gene abundances of N transformations using high-throughput 16S rRNA gene and ITS sequencing approaches. Two additional systems, a forest plantation (PF) and an abandoned agricultural field subject to natural succession (SUC), were also included for better assessment of the soil microbial community in terms of variation scale and regulatory importance of management intensity vs. plant type. Farming systems significantly affected the biodiversity of soil fungi but not bacteria, with Shannon index being the lowest in ORG. Bacterial and fungal communities in three cropping systems clustered and separated from those in PF and SUC, suggesting that management practices as such played minor roles in shaping the soil microbial community compared to plant type (i.e., woody vs. herbaceous plants). However, management practices prominently regulated habitat-specific taxa. Lecanoromycetes, a class of Ascomycota accounted for ∼10% of total fungal population in ORG, but almost nil in the other four systems. ORG also enriched bacteria belonging to the phyla, Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, and Gemmatimonadetes. Further, PICRUSt predicted that N-cycle community compositions varied with farming systems; compared to CON, ORG and ICL were more divergent from PF and SUC. Soil pH, together with inorganic N, extractable organic C, and soil organic C:N ratio explained < 50% of the total variations in both bacterial and fungal communities. Our data indicates that while moderately affecting the overall structure of the soil microbial community, management practices, particularly fertilization and the source of N (synthetic vs. organic), were important in regulating the presence and abundance of habitat-specific taxa.

Effects of co-composting of farm manure and biochar on plant growth and carbon mineralization in an alkaline soil

In the present study, the effects of co-composts of biochar (BC) and farm manure (FM) on the growth of wheat (Triticum aestivum L.) and carbon mineralization in an alkaline soil were investigated. The co-composts of FM and BC were prepared at various ratios (FM₁₀₀:BC₀, FM₇₅:BC₂₅, FM₅₀:BC₅₀, FM₂₅:BC₇₅, FM₀:BC₁₀₀) using aboveground piles and were used in two separate experiments conducted simultaneously. In the plant growth trial, prepared co-composts were applied at a rate of 2% w/w and wheat was grown at two fertilizer levels (half and full) until maturity. In the incubation experiment, same treatments were used and carbon mineralization was studied over a period of 79 days. The priming effect and net CO₂ efflux were calculated using CO₂ release data. Analysis of postincubation soil showed no significant effect of treatments on the pH of soil. However, electrical conductivity and organic matter were significantly influenced by all treatments. The increasing BC ratio in the compost reduced the carbon mineralization in soil in a dose-additive manner. Increase in BC proportion in composts (FM₅₀:BC₅₀, FM₂₅:BC₇₅, FM₀:BC₁₀₀) stabilized the native carbon of the soil and caused negative priming effect (-1.9, -5.6, and -8.48%, respectively). Regarding plant growth, the results showed an enhancement in the grain yield with the application of compost than control. Total nitrogen (N), phosphorus, and potassium (K) contents of the soil were also increased by the application of compost than control (un-amended soil). Significantly higher N and K concentrations in wheat plants were also examined when soil was treated with compost than control. The use of compost with half fertilizer was better in increasing grain yield, especially with higher BC proportion in the compost than FM.