The effect of biochar feedstock, pyrolysis temperature, and application rate on the reduction of ammonia volatilisation from biochar-amended soil

Mitigation of ammonia volatilization from organic and inorganic nitrogen sources applied to soil using water hyacinth biochars

The recent global population explosion has increased people's food demand. To meet this demand, huge amounts of nitrogen (N) fertilizer have been applied in the worldwide. However, ammonia (NH3) volatilization is one of the primary factors of N loss from soil after N application causing decrease crop N utilization efficiency and productivity. Incubation experiments were conducted on an acidic clayey soil with two different N sources (urea and anaerobic digestion effluent; ADE), two differently-produced biochars, and three biochar application rates (0%, 0.25%, and 1.0% w/w). Ammonia volatilization was lower from urea (14.0-23.5 mg N kg-1) and ADE (11.3-21.0 mg N kg-1) with biochar application than those without biochar (40.1 and 26.2 mg N kg-1 from urea and ADE alone, respectively). Biochar application significantly mitigated volatilization and reduction percentages for urea and ADE were 40%-64% and 18%-55%, respectively. 1.0% biochar application mitigated volatilization significantly compared to 0.25% application regardless of N source and biochar types. Possible mechanism for volatilization mitigation for urea and ADE were increased N immobilization by soil microorganisms and accelerated net nitrification rate due to increased soil nitrifying bacteria, respectively. Overall, our results clarified different mechanisms for N volatilization mitigation from different (inorganic vs. organic) N sources with biochar application.

Sustainable management of campus fallen leaves through low-temperature pyrolysis and application in Pb immobilization

Realizing campus sustainability requires the environmental-friendly and economical treatment of tremendous fallen leaves. Producing fallen leaf biochar at a low temperature is a candidate approach. In this study, six common types of fallen leaves on the campus were pyrolyzed at 300 °C. The obtained biochars were characterized and the adsorption mechanisms of lead (Pb) by the fallen leaf biochars were investigated. The adsorption capacity of leaf biochar for Pb was relatively high, up to 209 mg/g (Yulania denudata leaf biochar). Adsorption of Pb onto active sites was the rate-limiting step for most leaf biochars. But for Platanus leaf biochar, intraparticle diffusion of Pb2+ dominated owing to the lowest adsorption capacity. However, the highest exchangeable Pb fraction (27%) indicated its potential for removing aqueous Pb2+. Ginkgo and Prunus cerasifera leaf biochar immobilized Pb by surface complexation and precipitation as lead oxalate. Hence, they were suitable for soil heavy metal remediation. This study shed the light on the sustainable utilization of campus fallen leaves and the application of fallen leaf biochars in heavy metal remediation.

Evaluation Health Risks and Sorption of Hexavalent Chromium (Cr(VI) by Biochar and Iron Doped Zinc Oxide Modified Biochar (Fe-ZnO@BC) Using Trifolium: A Green Synthesis Technique

Contamination of aquatic and terrestrial environment with hexavalent chromium Cr(VI) is one of the major hazards worldwide due its carcinogenicity, persistency and immobility. Different research techniques have been adopted for Cr(VI) remediation present in terrestrial and aquatic media, while adsorption being the most advance, low cost, environmentally friendly and common method. The present study discussed the mechanisms of Parthenium hysterophorus derived biochar, iron-doped zinc oxide nanoparticles (nFe-ZnO) and Fe-ZnO modified biochar (Fe-ZnO@BC) involved in Cr(VI) mobility and bioavailability. Pot experiments were conducted to study the effect of Parthenium hysterophorus derived biochar, nFe-ZnO and Fe-ZnO@BC application rates (2%, 2 mg/kg, 10 mg/kg, respectively). The results indicated that the addition of soil amendments reduced Cr(VI) mobility. The findings revealed that the reduction in chromium mobility was observed by P. hysterophorus BC, and Fe-ZnO@BC but nFe-ZnO application significantly (p = 0.05) reduced Cr(VI) and CrT uptake as compared to the control treatments. The results of SEM coupled with EDS showed a high micropores and channel, smooth surface which helped in adsorption, and may enhance soil conditions. The concentration index (CI) by different amendments in trifolium plant was followed the descending order as: nFe-ZnO > Fe-ZnO@BC > P. hysterophorus BC after 30, 60 and 90 days of harvesting, respectively. In addition, human health risk index was found less than one (H1 < 1.0) in amended soils as compared to control treatments.

Pyrolysis temperature and time of rice husk biochar potentially control ammonia emissions and Chinese cabbage yield from urea-fertilized soils

Current agricultural practices are increasingly favoring the biochar application to sequester carbon, enhance crop growth, and mitigate various environmental pollutants resulting from nitrogen (N) loss. However, since biochar's characteristics can vary depending on pyrolysis conditions, it is essential to determine the optimal standard, as they can have different effects on soil health. In this study, we categorized rice husk biochars basis on their pH levels and investigated the role of each rice husk biochar in reducing ammonia (NH3) emissions and promoting the growth of Chinese cabbage in urea-fertilized fields. The findings of this study revealed that the variation in pyrolysis conditions of rice husk biochars and N rates affected both the NH3 emissions and crop growth. The neutral (pH 7.10) biochar exhibited effective NH3 volatilization reduction, attributed to its high surface area (6.49 m2 g-1), outperforming the acidic (pH 6.10) and basic (pH 11.01) biochars, particularly under high N rates (640 kg N ha-1). Chinese cabbage yield was highest, reaching 4.00 kg plant-1, with the basic biochar application with high N rates. Therefore, the neutral rice husk biochar effectively mitigate the NH3 emissions from urea-treated fields, while the agronomic performance of Chinese cabbage enhanced in all biochar amendments.

Impact of some amendments on kinetics of leaching dissolved organic carbon and ammonium in calcareous sandy soil under vinasse addition

The access of vinasse leachates to water bodies and groundwater exacerbates environmental problems, especially eutrophication. Therefore, a column experiment was performed to examine the effect of adding zeolite (ZL), bone char (BC), and wood chips biochar (WCB) in the presence of vinasse on carbon dioxide (CO2) emission, leaching dissolved organic carbon (DOC) and ammonium (NH4+) in calcareous sandy soil, as well as studying the kinetics of leaching dissolved organic carbon and ammonium. This column experiment contains four treatments: soil alone (CK), soil + zeolite (SZL), soil + bone char (SBC), and soil + wood chips biochar (SWCB). These amendments were applied to the soil at a level of 4%. Vinasse was added to all treatments at a level of 13 mL per column. The leached total cumulative DOC and total cumulative soluble ammonium amounts decreased significantly with applying ZL, BC, and WCB compared with the soil alone. The effectiveness of these amendments in lowering the total cumulative DOC leaching is in the order of SBC > SWCB > SZL > CK. However, the effectiveness of these amendments in decreasing the total cumulative NH4+ leaching is in the order of SZL > SWCB > SBC > CK. The rate constant (k) of DOC leaching decreased significantly with the application of bone char compared to soil alone treatment. In the presence of vinasse, the apparent half-life of leached DOC from the soil was 8.1, 12.9, 36.7, and 15.5 days for soil CK, SZL, SBC, and SWCB treatments, respectively. Half-life values of leached soluble ammonium from the soil in the presence of vinasse addition were 10.1, 39.5, 28.5, and 37.9 days for CK, SZL, SBC, and SWCB treatments, respectively. Amending soil with BC increased significantly the phosphorus availability, however, applying ZL and BC caused a significant increase in the available potassium in calcareous sandy soil compared to the control treatment. According to these results, it is recommended not to add vinasse alone to sandy soils, but it is preferred to be co-applied with BC amendment at the level of 4% better than ZL and WCB. This would decrease leaching DOC and ammonium to the water table and groundwater as well as enhance nutrient retention in the soil, which in turn, plays a vital role in reducing the harmful effect of vinasse and improving soil fertility.

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

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

Effects of five-year field aged zeolite on grain yield and reactive gaseous N losses in alternate wetting and drying paddy system

Clinoptilolite zeolite has been widely used in agricultural production systems for enhancing water and fertilizer savings, mitigating greenhouse gas emissions, and increasing yield. However, there is little information on field-aged effects of zeolite on reactive gaseous N losses under alternate wetting and drying irrigation (AWD). We conducted a five-year field experiment to investigate field-aged effect of natural zeolite addition at 0 (Z0), 5 (Z5), and 10 (Z10) t ha-1 on reactive gaseous N losses (NH3, N2O), N-related global warming potential (GWPN), soil properties and grain yield under two irrigation regimes (CF: continuous flooding irrigation; AWD) in the 4th (2020) and 5th (2021) years since its initial application in 2017. As compared with CF, AWD did not significantly affect grain yield and NH3 volatilization but increased seasonal N2O emissions by 46 %-71 % over two years. Zeolite increased rice yield for five consecutive years. Z10 reduced averaged cumulative NH3 volatilization and GWPN by 23 % and 26 %, compared to zeolite-free treatment, respectively, in the 4th and 5th years. Soil NH4+-N was increased with the increased rate of Z application under both CF and AWD. Z10 increased soil NH4+-N by 27 %-38 % and NO3--N by 14 %-22 % in five years, compared to Z0, respectively. Compared to AWD without zeolite, the addition of 10 t ha-1 zeolite under AWD lowered NH3 volatilization, cumulative N2O emissions, and GWPN by an average of 28 %, 29 %, and 30 % in two years, respectively. IAWDZ10 did not differ from ICFZ0 on reactive gaseous N losses but significantly lowered reactive gaseous losses relative to IAWDZ0. Therefore, zeolite addition could mitigate the reactive gaseous N losses and GWPN for at least five years after initial application, which is beneficial to promoting zeolite application and ensuring sustainable agriculture.

The increasing risk of ammonia volatilization in farmland from the recovery product of magnesium-modified biochar after nitrogen and phosphorus adsorption

Many studies have shown that magnesium modified biochar (MgBC) can recover nutrients from wastewater and be applied as an excellent slow-release fertilizer in farmland. However, the recovery products (NP-loaden MgBC), represented by struvite or magnesium phosphate, have a high degree of self-alkalinity, which may significantly increase the ammonia (NH3) volatilization in farmland. In this study, the optimal adsorption parameters, self-alkaline regulation process and co-adsorption mechanism of MgBC for ammonium ion (NH4+) and phosphate ion (PO43-) were studied through batch experiments. A field experiment was conducted with three treatments, including local conventional fertilization (N1B0) and the application of 5 t·ha-1 or 10 t·ha-1 NP-loaden MgBC in combination with local conventional fertilization (N1B1 and N1B2, respectively), to determine the impact of NP-loaden MgBC on NH3 volatilization, surface water c(NH4+-N) and pH. The results indicated that the maximum NH4+ and PO43- synergistic recovery of MgBC under the optimal adsorption parameters (dosage of 0.6 g·L-1; initial NH4+ and PO43- concentrations of 120 and 60 mg·L-1 and pH of 8) were 59.96 and 98.60 mg·g-1, respectively. Self-regulating alkaline MgBC maintained pH suitable for struvite, and precipitation mechanism controlled the adsorption. The presence of NP-loaden MgBC raised the pH levels in surface water during the basal fertilization stage and increased c(NH4+-N) in surface water during the topdressing stages. This, in turn, led to a significant increase in NH3 volatilization loss during the entire rice-growing period, with N1B1 and N1B2 experiencing a 23.87 % and 48.91 % increase respectively, compared to N1B0. Therefore, it is imperative to take into account the adverse impact of NP-laden MgBC on NH3 loss in paddy fields when considering its application in future field studies.

Hydrothermal carbonization of biogas slurry and cattle manure into soil conditioner mitigates ammonia volatilization from paddy soil

Hydrothermal carbonization of biogas slurry and animal manure into hydrochar could enhance waste recycling waste and minimize ammonia (NH3) volatilization from paddy fields. In this study, cattle manure-derived hydrochar prepared in the presence of Milli-Q water (CMWH) and biogas slurry (CMBSH), and biogas slurry-based hydrochar embedded with zeolite (ZHC) were applied to rice-paddy soil. The results demonstrated that CMBSH and ZHC treatments could significantly mitigate the cumulative NH3 volatilization and yield-scale NH3 volatilization by 27.9-45.2% and 28.5-45.4%, respectively, compared to the control group (without hydrochar addition), and significantly correlated with pH and ammonium-nitrogen (NH4+-N) concentration in floodwater. Nitrogen (N) loss via NH3 volatilization in the control group accounted for 24.9% of the applied N fertilizer, whereas CMBSH- and ZHC-amended treatments accounted for 13.6-17.9% of N in applied fertilizer. The reduced N loss improved soil N retention and availability for rice; consequently, grain N content significantly increased by 6.5-14.9% and N-use efficiency increased by 6.4-16.0% (P < 0.05), respectively. Based on linear fitting results, NH3 volatilization mitigation resulted from lower pH and NH4+-N concentration in floodwater that resulted from the acidic property and specific surface area of hydrochar treatments. Moreover, NH3-oxidizing archaea abundance in hydrochar-treated soil decreased by 40.9-46.9% in response to CMBSH and ZHC treatments, potentially suppressing NH4+-N transformation into nitrate and improving soil NH4+-N retention capacity. To date, this study applied biogas slurry-based hydrochar into paddy soil for the first time and demonstrated that ZHC significantly mitigated NH3 and increased N content. Overall, this study proposes an environmental-friendly strategy to recycle the wastes, biogas slurry, to the paddy fields to mitigate NH3 volatilization and increase grain yield of rice.

Synergistic effects of biochar derived from different sources on greenhouse gas emissions and microplastics mitigation during sewage sludge composting

This study aimed to investigate the effects of biochar derived from different sources (wheat straw, sawdust and pig manure) on greenhouse gas and microplastics (MPs) mitigation during sewage sludge composting. Compared to the control, all biochar significantly reduced the N2O by 28.91-41.23%, while having no apparent effect on CH4. Sawdust biochar and pig manure biochar significantly reduced the NH3 by 12.53-23.53%. Adding biochar decreased the global warming potential during composting, especially pig manure biochar (177.48 g/kg CO2-eq.). The concentration of MPs significantly increased in the control (43736.86 particles/kg) compared to the initial mixtures, while the addition of biochar promoted the oxidation and degradation of MPs (15896.06-23225.11 particles/kg), with sawdust biochar and manure biochar were more effective. Additionally, biochar significantly reduced the abundance of small-sized (10-100 μm) MPs compared to the control. Moreover, biochar might regulate specific microbes (e.g., Thermobifida, Bacillus and Ureibacillus) to mitigate greenhouse gas emissions and MPs degradation.

New insights into the production, characterization and potential uses of vineyard pruning waste biochars

Vineyard pruning waste (VP) can be converted into a useful char using pyrolysis as part of a valorization strategy. This study analyzed the effect of temperature (300 and 600 °C) and residence time (1 and 3 h) on an ample number of properties of VP derived biochars, including potential negative environmental impacts. The results showed a clear influence of temperature on biochar's properties and a weaker effect of residence time. Increasing temperature raised soil pH, electrical conductivity (EC), ash and C contents, aromaticity, specific surface area, solid density, mesoporosity and partial graphitization. However, higher pyrolysis temperature reduced O/C and N/C ratios, total N, P and Mg, and polycyclic aromatic hydrocarbons (PAHs). Particularly, the concentration of water extractable organic carbon (WEOC) decreased dramatically with pyrolysis temperature. Moreover, the WEOC fraction of biochars pyrolyzed at 300 °C exhibited a larger aromaticity than those pyrolyzed at 600 °C. Prolonged residence time increased ash content and fixed carbon (FC) and decreased H/C and O/C ratios; however, most frequently this parameter affected biochar properties following opposite trends for the two pyrolysis temperatures. Hydrophysical properties were adequate to consider VP derived biochars as growing media component. PAH concentration was much lower than thresholds following international standards. The germination index increased with temperature and decreased with residence time, so that phytotoxicity was observed in VP and in biochars pyrolyzed for 3 h. Our research demonstrates that, besides temperature, residence time can be useful to modulate the properties of biochars and that prolonged time effect is temperature-dependent.

Effects of fungal agents and biochar on odor emissions and microbial community dynamics during in-situ treatment of food waste

The effects of the co-addition of fungal agents and biochar on physicochemical properties, odor emissions, microbial community structure, and metabolic functions were investigated during the in-situ treatment of food waste. The combined addition of fungal agents and biochar decreased cumulative NH₃, H₂S, and VOCs emissions by 69.37%, 67.50%, and 52.02%, respectively. The predominant phyla throughout the process were Firmicutes, Actinobacteria, Cyanobacteria, and Proteobacteria. Combined treatment significantly impacted the conversion and release of nitrogen from the perspective of the variation of nitrogen content between different forms. FAPROTAX analysis revealed that the combined application of fungal agents and biochar could effectively inhibit nitrite ammonification and reduce the emission of odorous gases. This work aims to clarify the combined effect of fungal agents and biochar on odor emission and provide a theoretical basis for developing an environmentally friendly in-situ efficient biological deodorization (IEBD) technology.

Circular agriculture increases food production and can reduce N fertilizer use of commercial farms for tropical environments

World food production must increase in the coming years with minimal environmental impact for food and nutrition security. Circular Agriculture has emerged as an approach to minimize non-renewable resource depletion and encourage by-product reuse. The goal of this study was to evaluate Circular Agriculture as a tool to increase food production and N recovery. The assessment was conducted for two Brazilian farms (Farm 1; Farm 2) with Oxisols under no-till and a diversified cropping system, including five species of grain, three cover crop species, and sweet potato. Both farms implemented an annual two-crop rotation and an integrated crop-livestock system with beef cattle confined for 2-years. Grain and forage from the fields, leftovers from silos, and crop residues were used as cattle feed. Grain yield was 4.8 and 4.5 t ha^-1 for soybean, 12.5 and 12.1 t ha^-1 for maize, and 2.6 and 2.4 t ha^-1 for common bean, for Farm 1 and Farm 2, respectively, which is higher than the national average. The animals gained 1.2 kg day^-1 of live weight. Farm 1 exported 246 kg ha^-1 year^-1 of N in grains, tubers, and animals, while 216 kg ha^-1 year^-1 was added as fertilizer and N to cattle. Farm 2 exported 224 kg ha^-1 year^-1 in grain and animals, while 215 kg ha^-1 year^-1 was added as fertilizer and N to cattle. Circular practices, i.e., no-till, crop rotation, year-round soil covered, maize intercropped with brachiaria ruziziensis, biological N fixation, and crop-livestock integration, increased crop yield and decreased N application by 14.7 % (Farm 1) and 4.3 % (Farm 2). 85 % of the N consumed by the confined animals was excreted and converted into organic compost. Overall, circular practices associated with adequate crop management allowed recovering high rate of applied N, reducing environmental impacts, and increasing food production with lower production costs.

Effects of biochar in combination with varied N inputs on grain yield, N uptake, NH3 volatilization, and N2O emission in paddy soil

Biochar application can improve crop yield, reduce ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission from farmland. We here conducted a pot experiment to compare the effects of biochar application on rice yield, nitrogen (N) uptake, NH₃ and N₂O losses in paddy soil with low, medium, and high N inputs at 160 kg/ha, 200 kg/ha and 240 kg/ha, respectively. The results showed that: (1) Biochar significantly increased the rice grain yield at medium (200 kg/ha) and high (240 kg/ha) N inputs by 56.4 and 70.5%, respectively. The way to increase yield was to increase the rice N uptake, rice panicle number per pot and 1,000 grain weight by 78.5-96.5%, 6-16% and 4.4-6.1%, respectively; (2) Under low (160 kg/ha) N input, adding biochar effectively reduced the NH₃ volatilization by 31.6% in rice season. The decreases of pH value and NH₄⁺-N content in surface water, and the increases of the abundance of NH₄⁺-N oxidizing archaea and bacteria (AOA and AOB) communities contributed to the reduction of NH₃ volatilization following the biochar application; (3) Under same N input levels, the total N₂O emission in rice season decreased by 43.3-73.9% after biochar addition. The decreases of nirK and nirS gene abundances but the increases of nosZ gene abundance are the main mechanisms for biochar application to reduce N₂O emissions. Based on the results of the current study, adding biochar at medium (200 kg/ha) N level (N200 + BC) is the best treatment to synchronically reduce NH₃ and N₂O losses, improve grain yield, and reduce fertilizer application in rice production system.

Arbuscular Mycorrhizal Fungi Shift Soil Bacterial Community Composition and Reduce Soil Ammonia Volatilization and Nitrous Oxide Emissions

Arbuscular mycorrhizal fungi (AMF) establish mutualistic relationships with the majority of terrestrial plants, increasing plant uptake of soil nitrogen (N) in exchange for photosynthates. And may influence soil ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions directly by improving plant N uptake, and/or indirectly by modifying soil bacterial community composition for the soil C availability increasing. However, the effects of AMF on soil NH₃ volatilization and N₂O emissions and their underlying mechanisms remain unclear. We carried out two independent experiments using contrasting methods, one with a compartmental box device (in 2016) and the other with growth pot experiment (in 2020) to examine functional relationships between AMF and soil NH₃ volatilization and N₂O emissions under varying N input. The presence of AMF significantly reduced soil NH₃ volatilization and N₂O emissions while enhancing plant biomass and plant N acquisition, and reducing soil NH₄⁺ and NO₃^-, even with high N input. The presence of AMF also significantly reduced the relative abundance within the bacterial orders Sphingomonadales and Rhizobiales. Sphingomonadales correlated significantly and positively with soil NH₃ volatilization in 2016 and N₂O emissions, whereas Rhizobiales correlated positively with soil N₂O emissions. High N input significantly increased soil NH₃ volatilization and N₂O emissions with increasing relative abundance of Sphingomonadales and Rhizobiales. These findings demonstrate the contribution of AMF in regulating NH₃ and N₂O emission by improving plant N uptake and altering soil bacterial communities. They also suggest that altering the rhizosphere microbiome might offer additional potential for restoration of N-enriched agroecosystems.

Microplastics have rice cultivar-dependent impacts on grain yield and quality, and nitrogenous gas losses from paddy, but not on soil properties

Microplastics might affect the nitrogen (N)-use efficiency, crop production, and reactive N losses in agricultural system. However, it remains unclear whether the effects are dependent on crop cultivar. Here, a pot experiment was conducted to evaluate the effects of a typical polyethylene (PE) microplastics addition on grain yield and amino acid content, N-use efficiency, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission, and properties of paddy soil planted with common rice Nangeng 5055 (NG) and hybrid rice Jiafengyou 6 (JFY). The results showed that PE addition significantly reduced the grain yield and total grain amino acid content of hybrid rice by 23% and 1.7%, respectively. In addition, PE addition significantly decreased the N agronomic and recovery efficiencies of hybrid rice by 30% and 27%, respectively. For paddy soil in which hybrid rice was grown, PE addition significantly increased NH₃ volatilization by 72%, but exerted no influence on N₂O emission. Interestingly, the N₂O emission from NG+PE treatment was 15% significantly lower than that from NG treatment, which was associated with decreased gene copies of nirK (by 50%) and nirS (by 84%) in NG+PE treatment. Generally, no significant change in soil properties was found as result of microplastics addition regardless of the cultivar. In conclusion, the impacts of microplastics on rice production and quality, N-use efficiency and nitrogenous gas losses from paddy soil are cultivar-dependent.

Biochar-plant interaction and detoxification strategies under abiotic stresses for achieving agricultural resilience: A critical review

The unpredictable climatic perturbations, the expanding industrial and mining sectors, excessive agrochemicals, greater reliance on wastewater usage in cultivation, and landfill leachates, are collectively causing land degradation and affecting cultivation, thereby reducing food production globally. Biochar can generally mitigate the unfavourable effects brought about by climatic perturbations (drought, waterlogging) and degraded soils to sustain crop production. It can also reduce the bioavailability and phytotoxicity of pollutants in contaminated soils via the immobilization of inorganic and/or organic contaminants, commonly through surface complexation, electrostatic attraction, ion exchange, adsorption, and co-precipitation. When biochar is applied to soil, it typically neutralizes soil acidity, enhances cation exchange capacity, water holding capacity, soil aeration, and microbial activity. Thus, biochar has been was widely used as an amendment to ameliorate crop abiotic/biotic stress. This review discusses the effects of biochar addition under certain unfavourable conditions (salinity, drought, flooding and heavy metal stress) to improve plant resilience undergoing these perturbations. Biochar applied with other stimulants like compost, humic acid, phytohormones, microbes and nanoparticles could be synergistic in some situation to enhance plant resilience and survivorship in especially saline, waterlogged and arid conditions. Overall, biochar can provide an effective and low-cost solution, especially in nutrient-poor and highly degraded soils to sustain plant cultivation.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

Citric acid modified biochar application at a low dosage can synchronically mitigate the nitrogenous gas pollutants emission from rice paddy soils

Raw biochar with high pH possibly stimulated ammonia (NH₃) volatilization in the agricultural soil. We hypothesized that the modified biochar (MBC) with low pH can synchronically decrease the NH₃ and nitrous oxide (N₂O) losses. We performed a two-year experiment to clarify how citric acid MBC influence the NH₃ volatilization and N₂O emission as well as the underlying mechanisms. Two typical paddy soils, i.e., Hydragric Anthrosol and Haplic Acrisol, receiving equal urea N with 240 kg ha^-1 but varied rates of MBC with 0, 5, 10, and 20 t ha^-1 (named Urea, Urea + MBC5, Urea + MBC10, and Urea + MBC20, respectively) were studied. The results showed that MBC-amended treatments effectively mitigated the NH₃ volatilization from Hydragric Anthrosol and Haplic Acrisol by 29.6%-57.9% and 30.5%-62.4% in 2017, and by 16.5%-21.0% and 24.5%-35.0% in 2018, respectively, compared to Urea treatment. In addition, significantly lower N₂O emissions with averaged 38.3% and 43.1% in 2017, and 51.7% and 26.7% were recorded under Hydragric Anthrosol and Haplic Acrisol, respectively, following the MBC application (P < 0.05). Increased MBC addition performed higher efficacy on mitigating NH₃ volatilization, particularly in the first rice season, while this "dosage effect" was not found for N₂O reduction. Lowered pH in overlying water, enhanced adsorption of NH₄⁺-N and its nitrification rate likely contributed to the lower NH₃ volatilization as result of MBC addition. The nirS and nosZ gene copies were not changed by MBC, while the nirK gene copies were decreased as result of MBC amendment by 8.3%-25.2% under Hydragric Anthrosol and by 21.8%-24.9% under Haplic Acrisol. Consequent lower ratio of nirK/(nirS + nosZ) explained the mitigation effect of MBC on N₂O emission. In conclusion, the present two-year study recommends that MBC applied at a low dosage can perform positive effect on controlling the nitrogenous gas pollutants from paddy soil.

Enhancing N uptake and reducing N pollution via green, sustainable N fixation-release model

The overuse of N fertilizers has caused serious environmental problems (e.g., soil acidification, excessive N₂O in the air, and groundwater contamination) and poses a serious threat to human health. Improving N fertilizer utilization efficiency and plant uptake is an alternative for N fertilizers overuses. Enterobacter cloacae is an opportunistic pathogen, also used as plant growth-promoting rhizobacteria (PGPR), has been widely presented in the fields of bioremediation and bioprotection. Here we developed a new N fixation-release model by combining biochar with E. cloacae. The efficiency of the model was evaluated using a greenhouse pot experiment with maize (Zea mays L.) as the test crop. The results showed that biochar combined with E. cloacae significantly increased the N content. The application of biochar combined with E. cloacae increased total N in soil by 33% compared with that of N fertilizers application. The N-uptake and utilization efficiency (NUE) in plant was increased 17.03% and 14.18%, respectively. The activities of urease, dehydrogenase and fluorescein diacetate hydrolase (FDA) was improved, the catalase (CAT) activity decreased. Analysis of the microbial community diversity revealed the abundance of Proteobacteria, Actinobacteria, Firmicutes, and Gemmatimonadetes were significantly improved. The mechanism under the model is that E. cloacae acted as N-fixation by capturing N₂ from air. Biochar served as carrier, supporting better living environment for E. cloacae, also as adsorbent adsorbing N from fertilizer and from fixed N by E. cloacae, the adsorption in turn slower the N release. Altogether, the model promotes N utilization by plants, improves the soil environment, and reduces N pollution.

Ammonia volatilization mitigation in crop farming: A review of fertilizer amendment technologies and mechanisms

Good practices in controlling ammonia produced from the predominant agricultural contributor, crop farming, are the most direct yet effective approaches for mitigating ammonia emissions and further relieving air pollution. Of all the practices that have been investigated in recent decades, fertilizer amendment technologies are garnering increased attention as the low nitrogen use efficiency in most applied quick-acting fertilizers is the main cause of high ammonia emissions. This paper systematically reviews the fertilizer amendment technologies and associated mechanisms that have been developed for ammonia control, especially the technology development of inorganic additives-based complex fertilizers, coating-based enhanced efficiency fertilizers, organic waste-based resource fertilizers and microbial agent and algae-based biofertilizers, and their corresponding mechanisms in farmland properties shifting towards inhibiting ammonia volatilization and enhancing nitrogen use efficiency. The systematic analysis of the literature shows that both enhanced efficiency fertilizers technique and biofertilizers technique present outstanding ammonia inhibition performance with an average mitigation efficiency of 54% and 50.1%, respectively, which is mainly attributed to the slowing down in release and hydrolysis of nitrogen fertilizer, the enhancement in the adsorption and retention of NH₄⁺/NH₃ in soil, and the promotion in the microbial consumption of NH₄⁺ in soil. Furthermore, a combined physical and chemical means, namely membrane/film-based mulching technology, for ammonia volatilization inhibition is also evaluated, which is capable of increasing the resistance of ammonia volatilization. Finally, the review addresses the challenges of mitigating agricultural ammonia emissions with the aim of providing an outlook for future research.

Iron-Modified Biochar Strengthens Simazine Adsorption and Decreases Simazine Decomposition in the Soil

Currently, modified biochar has been successfully used in the remediation of soil polluted with heavy metals. However, the effects of the modified biochar on pesticides (such as simazine) are still unclear. Herein, the environmental fate of simazine, such as decomposition, leaching, and adsorption in unamended soil, in the soil amended with unmodified and modified biochar (biochar + FeCl₃, biochar + FeOS, biochar + Fe) were evaluated. In addition, an incubation experiment was also performed to observe the influence of modified biochar on the microbial community and diversity in the soil. The results showed that modified biochar significantly decreased the decomposition of simazine in the soil compared to its counterpart. Modified biochar also reduced the concentration of simazine in the leachate. Compared with the control, soil microbial biomass in the soil amended with unmodified biochar, biochar + FeCl₃, biochar + Fe, and biochar + FeOS was decreased by 5.3%, 18.8%, 8.7%, and 18.1%, respectively. Furthermore, modified biochar changed the structure of the microbial community. This shows that modified biochar could increase the soil adsorption capacity for simazine and change the amount and microbial community that regulates the fate of simazine in the soil. This study concludes that iron-modified biochar has positive and negative effects on the soil. Therefore, its advantages and side effects should be considered before applying it to the soil.

Banana, pineapple, cassava and sugarcane residue biochars cannot mitigate ammonia volatilization from latosols in tropical farmland

Ammonia (NH₃) volatilization is a major pathway of soil nitrogen loss in tropical farmland, causing many environmental issues. Biochar can improve soil quality and affect soil NH₃ volatilization. However, little is known about the effects of tropical crop residue biochar on soil NH₃ volatilization in tropical farmland. Therefore, a laboratory incubation study was conducted using four kinds of tropical crop residue biochar (pineapple straw (stem and leaves), banana straw, cassava straw and sugarcane bagasse pyrolyzed at 500 °C) with five addition rates (0.5%, 1%, 2%, 4%, and 6%) to evaluate their impact on NH₃ volatilization from tropical latosols. The results showed that NH₃ volatilization peaked twice under biochar application, once at 1-5 days and again at 12-16 days. The cumulative NH₃ volatilization (0.14-0.47 mg kg^-1) of the 20 biochar treatments was higher than that of the control (0.12 mg kg^-1). With the increase in the biochar addition rate, the soil pH, soil organic matter (SOM), urease activity, nitrate nitrogen content (NO₃^--N), nitrification rate and cumulative NH₃ volatilization increased gradually, and the 6% biochar treatment resulted in the highest NH₃ volatilization loss (0.19-0.47 mg kg^-1). The type of biochar is also a main factor affecting soil NH₃ volatilization. The cumulative NH₃ volatilization was the highest under pineapple straw biochar, as it was 19-43% higher than when the other three biochars were applied. However, sugarcane bagasse biochar had the lowest cumulative NH₃ volatilization due to its low quartz, sylvite and calcite contents, lack of -OH hydroxyl groups and high adsorbability. NH₃ volatilization was positively correlated with the soil pH, SOM, urease activity, NO₃^--N and nitrification rate. In conclusion, four tropical crop residue biochars can increase NH₃ volatilization in tropical latosols, so reducing NH₃ volatilization needs to be further considered in tropical crop residue biochar applications.

Recent Advances on Waste Plastic Thermal Pyrolysis: A Critical Overview

Post-consumer plastic management, otherwise termed waste plastic (WP) management, is a great challenge in today’s world, mainly because of its characteristic biodegradation properties. The quantity of waste plastics correspondingly increases with the increase in demand for plastic use. Research has shown that this demand increases yearly. Most of these waste plastics include high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET) and polystyrene (PS). Potentially, these wastes are a wealth, and studies have explored that pyrolysis is a reputable mechanism to accomplish this. In this critical review, an extensive investigation on waste plastics thermal pyrolysis (WPTP) is carried out. The factors that affect the product’s yield and selectivity are discussed, and a comparative quality guarantee of WPTP is examined. This paper presents an assurance into the current findings of WPTP and reveals some common gaps and misconceptions surrounding this field, which are recommendable towards the support of further research work. The significant role of co-pyrolysis of plastics with biomass in this field is also emphasised, and a glimpse into the influence of mixed waste plastics in pyrolysis is presented.

Impact of Biochar Application on Ammonia Volatilization from Paddy Fields under Controlled Irrigation

Ammonia volatilization is an important nitrogen loss pathway in the paddy field ecosystem which leads to low nitrogen-utilization efficiency and severe atmospheric pollution. To reveal the influence and the mechanism of biochar application on ammonia volatilization from paddy fields under controlled irrigation, field experiments were conducted in the Taihu Lake Basin in China. The experiment consisted of three levels of biochar application (0, 20, and 40 t·ha−1) and two types of irrigation management (controlled irrigation and flood irrigation). Increasing ammonia volatilization occurred after fertilization. Biochar application reduced the cumulative ammonia volatilization from controlled-irrigation paddy fields, compared with non-biochar treatment. The cumulative ammonia volatilization in controlled-irrigation paddy fields with 40 t·ha−1 biochar application was reduced by 12.27%. The decrease in ammonia volatilization was related to the change in soil physical and soil physical–chemical properties and soil microbial activities. The high biochar application (40 t·ha−1) increased the NH4+-N content in soil (p < 0.01) and soil solution (p <0.05), increased by 64.98% and 19.72%, respectively. The application also increased the soil urease activity (p < 0.01), and high biochar application (40 t·ha−1) increased soil urease activity by 33.70%. Ammonia volatilization from paddy fields was significantly correlated with the nitrogen concentration (p < 0.01) in the soil solution and soil urease activity (p < 0.05). Meanwhile, the abundance of ammonia monooxygenase subunit A (AOA) and ammonia-oxidizing bacteria (AOB) with biochar application under controlled irrigation showed an increasing trend with rice growth. The long-term application of biochar may have a relatively strong potential to inhibit ammonia volatilization. In general, the combined application of controlled irrigation and biochar provides an eco-friendly strategy for reducing farmland N loss and improving paddy field productivity.

Biochar-N fertilizer interaction increases N utilization efficiency by modifying soil C/N component under N fertilizer deep placement modes

The situation of imbalance application of nitrogenous fertilizers in maize production is a serious issue in China, and excessive nitrogen (N) application is hazardous to sustainable agricultural production and environment. In this experiment, two biochar levels (C0: 0, C1: 2 %), three different N rates (N1: 50, N2: 100, and N3: 200 mg kg^-1), and two fertilization methods (T: traditional N fertilizer application mode and D: deep N fertilizer placement mode) were set up to study the response of different treatments on maize yield, N uptake, and N use efficiency. Herein, we found that fresh and dry biomasses were increased by 292 % and 283 % under C1N3 treatment with the deep application of N fertilizer compared to the control treatment (without nitrogen fertilizers and biochar). According to structural equation modeling (SEM), soil physical and chemical properties, N component and C component in different soil layers were associated with biochar and N fertilizer treatment, especially at 20-40 depth. The combination of N fertilizer and biochar application promoted the effects of biochar on the improving NUE of plants. The biochar alleviated the loss of soil nitrogen (from 52.00 to 25.94 %) under traditional N fertilizer application. Overall, excessive input of N fertilizer not only promotes the growth of crops but also causes a waste of resources and environmental pollution. We suggest that combined application of biochar and N fertilizer could significantly reduce N loss, and improve root growth and N uptake, resulting in improving NUE by improving soil environment (pH, SOM, EC) and adjusting soil C/N component.

Novel agrotechnological intervention for soil amendment through areca nut husk biochar in conjunction with vetiver grass

Soil quality management through effective utilization of agricultural residue is the cynosure of intense global research. Therefore, we have explored the pyrolytic conversion of a locally available agricultural residue, the areca nut husk (AH), into biochar (BC) as a sustainable option towards residue management. The AH was carbonized at 250-400 °C, and residence times of 30-90 min. Subsequent detailed analysis revealed areca nut husk biochar (AHBC) formed at 250 °C with 60 min residence time, had the highest soil organic matter yield index (SOMYI), the lowest H/C and O/C ratio, and an average particle size of 1191.6 nm. Further characterization exposed the highly porous structure of prepared AHBC with oxygenated functional groups attached to its surface. The application of AHBC in conjunction with vetiver (Chrysopogon zizanioides L.) was used as a novel agrotechnological approach to assess soil quality improvement. Various doses of AHBC (5 t ha^-1, 10 t ha^-1, and 15 t ha^-1) were applied in the experimental soils, and the principal component analysis (PCA) revealed that the 15 t ha^-1 dose was optimum for the growth of the vetiver. AHBC amendment in soil resulted in increase of plant height and relative water content. This could be attributed to the increase in organic carbon, cation exchange capacity, and nutrients in the soil. Application of AHBC along with vetiver could be a simple, yet effective option, for sustainable agricultural residue and soil management.

Combined biochar and double inhibitor application offsets NH3 and N2O emissions and mitigates N leaching in paddy fields

The effects of combined biochar and double inhibitor application on gaseous nitrogen (N; nitrous oxide [N₂O] and ammonia [NH₃]) emissions and N leaching in paddy soils remain unclear. We investigated the effects of biochar application at different rates and double inhibitor application (hydroquinone [HQ] and dicyandiamide [DCD]) on NH₃ and N₂O emissions, N leaching, as well as rice yield in a paddy field, with eight treatments, including conventional urea N application at 280 kg N ha^-1 (CN); reduced N application at 240 kg N ha^-1 (RN); RN + 7.5 t ha^-1 biochar (RNB1); RN + 15 t ha^-1 biochar (RNB2); RN + HQ + DCD (RNI); RNB1 + HQ + DCD (RNIB1); RNB2 + HQ + DCD (RNIB2); and a control without N fertilizer. When compared with N leaching under RN, biochar application reduced total N leaching by 26.9-34.8% but stimulated NH₃ emissions by 13.2-27.1%, mainly because of enhanced floodwater and soil NH₄⁺-N concentrations and pH, and increased N₂O emission by 7.7-21.2%, potentially due to increased soil NO₃^--N concentrations. Urease and nitrification inhibitor addition decreased NH₃ and N₂O emissions, and total N leaching by 20.1%, 21.5%, and 22.1%, respectively. Compared with RN, combined biochar (7.5 t ha^-1) and double inhibitor application decreased NH₃ and N₂O emissions, with reductions of 24.3% and 14.6%, respectively, and reduced total N leaching by up to 45.4%. Biochar application alone or combined with double inhibitors enhanced N use efficiency from 26.2% (RN) to 44.7% (RNIB2). Conversely, double inhibitor application alone or combined with biochar enhanced rice yield and reduced yield-scaled N₂O emissions. Our results suggest that double inhibitor application alone or combined with 7.5 t ha^-1 biochar is an effective practice to mitigate NH₃ and N₂O emission and N leaching in paddy fields.

Effects of feedstock and pyrolysis temperature of biochar on promoting hydrogen production of ethanol-type fermentation

Biochar has been shown to benefit fermentative hydrogen production. However, the influencing factors and key characteristics of its promoting function remained to be elucidated. This study investigated the effects of two crucial factors, feedstock and pyrolysis temperature, on the hydrogen production-promoting function of biochar in ethanol-type fermentation. The physicochemical characteristics and promoting effects of biochars prepared with five biomass wastes (coffee ground, corn stalk, Ginkgo biloba leaf, mealworm frass, and sugarcane bagasse) were determined. Sugarcane bagasse-derived biochar (SBBC) showed the best hydrogen production-promoting effect in ethanol-type fermentation. The physicochemical properties of biochar, such as pH, element composition and surface features, were significantly affected by pyrolysis temperature, but the promoting effects were not significantly changed. The hydrogen production-promoting effect of biochar in ethanol-type fermentation was mainly affected by feedstock instead of pyrolysis temperature. A potential promoting mechanism was proposed that biochar prepared at low temperature boosted the hydrogen production with redox activity, while that at high temperature achieved the promotion via cell growth enhancement. This study revealed the key promoting factor of biochar in ethanol-type fermentative hydrogen production, and provided novel insights for the promoting mechanism of biochar.

Water-washed hydrochar in rice paddy soil reduces N2O and CH4 emissions: A whole growth period investigation

Hydrochar (HC), an environment-friendly material, enhances soil carbon sequestration and mitigate greenhouse gases (GHGs) emissions in croplands. In this study, the water-washed HC (WW-HC) was applied to paddy soil to investigate effects on nitrous oxide (N₂O) and methane (CH₄) emissions during rice growth period. Four treatments, namely control (without N fertilizer and WW-HC), N fertilizer (WW-HC00), N fertilizer with 0.5 wt% WW-HC (WW-HC05) and N fertilizer with 1.5 wt% WW-HC (WW-HC15), were established. Results showed the WW-HC addition reduced N₂O and CH₄ emissions, global warming potential (GWP) and greenhouse gas intensity (GHGI) during the growing season. Moreover, the WW-HC application reduced N₂O cumulative emission (P < 0.05) (by 28.6% and 23.8% for WW-HC05 and WW-HC15, respectively). It was mainly due to the reduced ratio of (nirK + nirS) to nosZ under WW-HC15 (P < 0.05). Compared with WW-HC00, the WW-HC05 reduced CH₄ cumulative emissions by 14.8%, while the WW-HC15 increased by 9.7%. This might be ascribed to the significantly reduced expression of the methanogenic mcrA gene and ratio of mcrA to pmoA by WW-HC (P < 0.05). The WW-HC05 amendment decreased GWP and GHGI by 18.6% and 32.5%, respectively. Furthermore, the WW-HC application greatly improved nitrogen use efficiency by 116-145% compared with the control. Our study indicates the WW-HC application is a promising GHGs mitigation practice in paddy fields.

Co-application of high temperature biochar with 3,4-dimethylpyrazole-phosphate treated ammonium sulphate improves nitrogen use efficiency in maize

This study aimed on the increasing nitrogen use efficiency (NUE) of maize via the use of high temperature produced biochar (700 °C). Maize was grown to maturity on two contrasting soils (acidic Cambisol and neutral Chernozem) in pots with a treatment of biochar co-applied with ammonium sulphate stabilised by a nitrification inhibitor (3,4-dimethylpyrazole-phosphate, DMPP) or un-stabilised. The combination of biochar with ammonium sulphate containing DMPP increased maize biomass yield up to 14%, N uptake up to 34% and NUE up to 13.7% compared to the sole application of ammonium sulphate containing DMPP. However, the combination of biochar with un-stabilised ammonium sulphate (without DMPP) had a soil-specific influence and increased maize biomass only by 3.8%, N uptake by 27% and NUE by 11% only in acidic Cambisol. Further, the biochar was able to increase the uptake of phosphorus (P) and potassium (K) in both stabilised and un-stabilised treatments of ammonium sulphate. Generally, this study demonstrated a superior effect from the combined application of biochar with ammonium sulphate containing DMPP, which improved NUE, uptake of P, K and increased maize biomass yield. Such a combination may lead to higher efficiency of fertilisation practices and reduce the amount of N fertiliser to be applied.

Comparison of 17β-estradiol adsorption on soil organic components and soil remediation agent-biochar

Steroid estrogen residues (SEs) in the soil have attracted growing attention because of their potential for endocrine disruption. Soil organic matter (SOM) and soil remediation agent-biochar, both have important influences on the fate of SEs in the soil environment. This study compared the adsorption of 17β-estradiol (E2) on wheat straw biochar (W-BC) and cow manure biochar (C-BC) with main SOM components including biomacromolecules (cellulose, collagen and lignin) and humic acids (HA). The impact of pyrolysis temperature (350 °C, 550 °C, and 700 °C) on the adsorption capacity of biochar and different concentrations NaClO oxidation on the adsorption capacity of HA were also investigated. The experimental results showed that the adsorption of E2 by biomolecules conformed to the linear isotherm (R² > 0.88), and the adsorption of E2 on biochars and HA were well described by the Langmuir and Freundlich isotherm (R² > 0.94). Meanwhile, the order of the E2 adsorption capacity of sorbents was W-BC > C-BC > HA > lignin > collagen > cellulose. The adsorption capacity of biochar and SOM for E2 increased with the enhancement of aromaticity and hydrophobicity and the reduction of polarity. In addition, the increase of pyrolysis temperature of biochars also promoted the adsorption capacity of E2, while oxidation treatment with NaClO reduced the adsorption capacity of HA to E2. These results deepened the understanding of the adsorption behaviour of E2 on SOM and biochar, and expanded the understanding of the behaviour of SEs in the soil environment.

Carbon sequestration, kinetics of ammonia volatilization and nutrient availability in alkaline sandy soil as a function on applying calotropis biochar produced at different pyrolysis temperatures

This incubation study assessed the effects of unpyrolyzed Calotropis procera and its biochar produced at different pyrolysis temperatures as well as incubation periods on carbon (C) emission, ammonia (NH₃) volatilization, soil quality indicators and nutrient availability of alkaline sandy soil. Five treatments were studied in this experiment: unamended soil (CK), unpyrolyzed calotropis (UPC), calotropis biochar at 250 °C (CB250), calotropis biochar at 400 °C (CB400), and calotropis biochar at 650 °C (CB650). These amendments were applied to the soil at level of 4% (w/w). The results of this study showed that applying unpyrolyzed calotropis residues increased cumulative CO₂ emission from the soil by 117.3, 239.4 and 232.0% over CB250, CB400, and CB650, respectively, by the end of incubation. Compared to the unamended soil, applying CB250 reduced cumulative NH₃ volatilization in soil by 71.5%, which attributed to ammonia adsorption because of increased cation exchange capacity and decreased soil pH, but CB650 increased cumulative NH₃ volatilization by 73.3% after the 3-day incubation as a result of high soil pH. The available phosphorus in soil improved significantly (p ≤ 0.01) with adding unpyrolyzed calotropis residues and its biochar produced at different pyrolysis temperatures compared to the unamended soil. The values of available phosphorus in the soil under study influenced significantly by pyrolysis temperatures of produced biochar; this is due to the pyrolysis of feedstocks increases labile phosphorus. Thenceforth, using biochar is an important strategy for enhancing carbon sequestration, decreasing ammonia volatilization and improving soil quality parameters in arid regions.

Biochar production and applications in agro and forestry systems: A review

Biochar is a product of biomass thermochemical conversion. Its yield and quality vary significantly with the production technology and process parameters, which also affect its performance in agro and forestry systems. In this review, biochar production technologies including slow pyrolysis, fast pyrolysis, gasification, and torrefaction were compared. The yield of biochar was found to decrease with faster heating rate or more oxygen available. The benefits of biochar application to agro and forestry systems were discussed. Improvements in soil health, plant growth, carbon sequestration, and greenhouse gas mitigation are apparent in many cases, but opposite results do exist, indicating that the beneficial aspect of biochar are limited to particular conditions such as the type of biochar used, the rate of application, soil type, climate, and crop species. Limitations of current studies and future research needed on biochar are also discussed. Specifically, the relationships among biochar production technologies, biochar properties, and biochar performance in agro and forestry systems must be better understood.

Physicochemical characteristics of biochars can be beneficially manipulated using post-pyrolyzed particle size modification

This work aimed to study the changes in the physicochemical properties of biochars induced by post-pyrolyzed particle size processing. Twelve distinct physicochemical attributes of four different particle sized biochars, derived from three different feedstocks, including rice husk, tea wastes and woodchips; were investigated. Amongst all of the investigated characteristics water repellency (η2 = 0.99) and mean pore diameter (η2 = 0.95) were the characteristics most affected by feedstock type and particle size, respectively. The interaction effect between biochar type and particle size was extremely significant (P < 0.001) for surface area and mean pore diameter. While feedstock mainly controlled biochar characteristics, most characteristics were also particle size dependent, where size dependency was more influential on physical than chemical properties. For most properties a significant interaction effect between biochar type and particle size was also detected.

The characteristics of oestrone mobility in water and soil by the addition of Ca-biochar and Fe-Mn-biochar derived from Litchi chinensis Sonn

In this study, the effect of biochar (BC) derived from Litchi chinensis Sonn. and its modification, including Ca-biochar (Ca-BC) and Fe-Mn-biochar (Fe-Mn-BC), on the transportation of oestrone (E1) in water and soil was investigated. Fe-Mn-BC showed better adsorption ability than other types of biochar (BC, Ca-BC) under different conditions (humic acid, pH, ionic strength) in an aqueous environment. The maximum mass of sorbent at 298 K increased from 1.12 mg g^-1 (BC) to 4.18 mg g^-1 (Fe-Mn-BC). Humic acid had a greater impact on aqueous E1 adsorption on these biochars than did the pH and ionic strength. Fe-Mn-BC as a soil amendment had a great control of E1 transport in soil, and no leachate of E1 was observed in the column experiment. E1 mobility showed strong retardation in amended soil with Ca-BC (R_f = 11.2) compared with raw soil (R_f = 7.1). These results suggested that Fe-Mn-BC was more effective in controlling E1 transportation, and Fe-Mn-BC could be used as an alternative and inexpensive adsorbent to reduce E1 contaminants from water and soil.

Bentonite hydrochar composites mitigate ammonia volatilization from paddy soil and improve nitrogen use efficiency

Clay-hydrochar composites (CHCs) are of great significance in ammonium (NH₄⁺) adsorption and have the potential to be applied to paddy fields to prevent ammonia (NH₃) volatilization. In this study, three CHCs were produced by infusing different clays to poplar-sawdust-derived hydrochar, including a bentonite hydrochar composite (BTHC), montmorillonite hydrochar composite (MTHC), and kaolinite hydrochar composite (KTHC). These three CHCs were applied to a paddy soil column system growing rice. The temporal variations in NH₃ volatilization and NH₄⁺ loss in floodwater were monitored after three fertilization dates. The results showed that among the three CHCs, only the BTHC significantly reduced cumulative NH₃ volatilization (by 41.8%), compared to that of the unamended control (without addition of hydrochar or clay-hydrochar-composite). In the unamended control, NH₃ volatilization loss accounted for 31.4% of the applied N fertilizer; with the BTHC amendment, NH₃ volatilization loss accounted for 17.4% of the applied N fertilizer. The reduced N loss via the BTHC amendment resulted in an increased N supply and further improved the N use efficiency and yield by 37.36% and 18.8% compared to that of the control, respectively. The inhibited NH₃ volatilization was mainly attributed to the increased soil NH₄⁺ retention as a result of BTHC's larger pore volume and specific surface area. In addition, the BTHC treatment significantly reduced the abundance of archaeal amoA genes (AOA), which possibly inhibited nitrification and increased soil NH₄⁺ retention. This study, for the first time, screened BTHC as an excellent material for mitigating NH₃ volatilization from paddy fields. The reduced NH₃ volatilization loss might contribute to increased soil N retention and plant N use efficiency.

Microalgae-derived hydrochar application on rice paddy soil: Higher rice yield but increased gaseous nitrogen loss

Hydrothermal carbonization represents a promising technique for transforming microalgae into the hydrochar with abundant phytoavailable nutrients. However, the effects of microalgae-derived hydrochars on the gaseous nitrogen (N) loss from agricultural field are still unclear. Chlorella vulgaris powder (CVP) and two Chlorella vulgaris-derived hydrochars that employ water (CVHW) or citrate acid solution (CVHCA) as the reaction medium were applied to a soil column system grown with rice. The temporal variations of nitrous oxide (N₂O) emissions and ammonia (NH₃) volatilization were monitored during the whole rice-growing season. Results showed that CVHW and CVHCA addition significantly increased the grain yield (by 13.5-26.8% and 10.5-23.4%) compared with control and CVP group, while concomitantly increasing the ammonia volatilization (by 53.8% and 72.9%) as well as N₂O emissions (by 2.17- and 2.82-fold) from paddy soil compared to control. The microbial functional genes (AOA, AOB, nirk, nirS, nosZ) in soil indicated that CVHW and CVHCA treatment stimulated the nitrification and denitrification, and inhibited the N₂O oxidation in soil. Notably, CVHW was recommended in the view of improving yield and controlling NH₃ volatilization because no significant difference of the yield-scale NH₃ volatilization was detected between control and CVHW treatment. This study for the first time uncovered that Chlorella vulgaris-derived hydrochars have positive effects on rice N utilization and growth but negative effects on the atmospheric environment.

Mechanisms of Pb and/or Zn adsorption by different biochars: Biochar characteristics, stability, and binding energies

Biochar has been widely studied as an amendment for use in remediation of water and soil contaminated with heavy metals such as Pb²⁺ and Zn²⁺, but the effects of biochar characteristics, including stability, on the competitive adsorption of Pb²⁺ and Zn²⁺ by biochars from various sources are incompletely understood. In this work, biochars from three different feedstocks, including rice straw (RS), chicken manure (CM), and sewage sludge (SS), were prepared at two pyrolysis temperatures, 550 and 350 °C, and tested to investigate the influence of their stabilities and other characteristics on their adsorption of Pb²⁺ and Zn²⁺ in both single- and binary-metal systems. RS biochar had the highest carbon and hydrogen contents, greatest number of functional groups (e.g., OH and C=C/C=O), highest pH, most negative surface charge, and highest physical stability, and thus the highest adsorption capacity for Pb²⁺ and Zn²⁺. Pyrolysis at the higher temperature resulted in a slight decrease in aromatic functional groups on biochar surfaces but higher adsorption capacities for Pb²⁺ and Zn²⁺ due to the decreased biochar particle size and increased specific surface area. FTIR, XRD, and XPS analyses indicated that Pb²⁺ and Zn²⁺ were absorbed on the biochars primarily via chemical complexation with aromatic functional groups. Quantum chemistry calculations confirmed that these functional groups (e.g., -OH and-COOH) tended to bind more strongly with Pb²⁺ than with Zn²⁺ due to the former's lower binding energies, which also accounted for the notable decrease in adsorption of Zn²⁺ in the presence of Pb²⁺. In addition, compared to carboxyl groups, hydroxyl groups had smaller binding energies and stronger metal complexation. These findings provide a theoretical basis for improved understanding of potential applications of biochars in environmental remediation.

Relevance of biochar to influence the bacterial succession during pig manure composting

The influence of pig manure biochar amendment (PMBA) during the pig manure (PM) and wheat straw (WS) composting was evaluated. Five concentration of PMBA (0%, 2%, 4%, 6% and10%) were applied to explore the bacterial distributions in PM compost by 16SDNA amplicons sequencing. The results showed that the addition of 6% PMBA could significantly enhanced the bacterial community abundance compared with other composts, while control has relative less bacterial population (332 OTU). The visualization of phylogenetic tree and krona demonstrated the distinctive distribution of each composts, suggested that biochar dosages have an influence on bacterial communities' variation during co-composting. Beta-diversity of distance matrix heat-map and principal component analysis confirmed that bacterial communities were considerably correlated with increasing PMBA. Redundancy also confirmed the similarity and discrepancy among all treatments and environmental factors. This work considered as the potential of PMBA as a booster in composting, where T4 has most plentiful bacterial community and diversity.

Responses of ammonia volatilization from rice paddy soil to application of wood vinegar alone or combined with biochar

Wood vinegar (WV) was applied alone or combined with biochar (BC) to observe their efficiency on suppressing the ammonia (NH₃) volatilization from rice paddy soil. Five treatments, i.e., control (240 kg N ha^-1 applied in urea), WV-5 and WV-10 (240 kg N ha^-1 plus 5 and 10 t WV ha^-1, respectively), and their counterparts WV-5-BC and WV-10-BC (WV-5 and WV-10 plus 7 t BC ha^-1), were evaluated by a soil columns experiment. The N fertilizer was split applied as basal and two supplementary fertilizations (named BF, SF1 and SF2, respectively). The results showed that WV-5 treatment increased rice grain yield up to 11.2% compared to the control. Compared with the control, four WV-amended treatments, exhibited lower pH values of the floodwater (7.94-8.18 vs 8.47 and 7.85-7.91 vs 7.98) and the topsoil (6.52-6.76 vs 6.82 and 6.82-6.92 vs 6.99) during the BF and SF1 periods. Both WV-5 and WV-10 increased the NH₄⁺-N contents of topsoil by 10.9-17.8% and 16.1-36.2% after BF and SF1, respectively, than control treatment. Additionally, the floodwater of the WV-amended treatments had higher NH₄⁺-N concentration than control during the first three days after N fertilization, which can be attributed to the stimulating effect of WV on soil urease enzyme activity. WV did not effectively reduce NH₃ volatilization as hypothesized. Interestingly, four WV-amended had relatively reduced the yield-scale NH₃ volatilization by 13.6% than the control. It is suggested that WV needs to be applied with BC at a moderate rate to achieve optimum rice yield and mitigate NH₃ volatilization.

Biochar-based nitrogen fertilizers: Greenhouse gas emissions, use efficiency, and maize yield in tropical soils

The sustainable development of agriculture depends on increasing N use efficiency (NUE) and consequently reducing N losses from different sources, such as NH₃ volatilization, NO₃^- leaching, and N₂O emissions. While the chemical and physical properties of biochar (BC) in fertilizers have been evaluated to increase NUE, a lack of information exists regarding the effects of BC amendments in tropical soils. We performed a one-year field experiment with tropical soil to evaluate the effects of BC-based N fertilizers (BN) on maize yield and on greenhouse gas (GHG) emissions. The treatments consisted of five fertilizers: ammonium nitrate (AN), urea (U), BN_51/10 (51% BC, 10% N), BN_40/17 (40% BC, 17% N), BN_29/20 (29% BC, 20% N), and a control (without N fertilizer). The N fertilizers (80 kg N ha^-1) were broadcast 20 days after sowing. Yield, grain N uptake, NUE, ammonia volatilization, and GHG emissions were measured. The results demonstrated the potential of BNs to enhance the efficiency of the fertilizers. BN_51/10 and BN_40/17 had an average maize yield that was 26% higher than that of U, and BN_51/10 resulted in a NUE that was 12% higher than what was observed for U. Both the effects on yield and NUE were attributed to lower N release rates of the BN-amended fertilizers compared to that of the conventional soluble N sources. The BC-based fertilizers presented better environmental performance, and BN_51/10 showed the lowest emission intensity when C sequestration by BC was not considered, with a value that was 14% lower than that of the U treatment. When considering C sequestration by BC, the emission intensity of the C equivalents demonstrated that all BNs presented C sequestration that differed from that of the mineral N sources. BC-based nitrogen fertilizers may have promising applications for sustainable agricultural development by mitigating N losses and increasing C stocks.

Effect of biochar and bacterial inoculum additions on cow dung composting

The present study evaluates the effectiveness of different types of biochar additives and bacterial inoculation on gaseous emission, nutrient preservation, and relevant functional bacterial community during cow manure composting. The result revealed that biochar and bacterial consortium inoculation effectively inhibited gaseous emission and improved carbon and nitrogen sequestration, remarkably enriching the abundance of the functional bacteria community. Notably, superior efficacy was found in 12% wheat straw biochar and bacterial consortium amendment composting of T6 with the lowest cumulative CO₂-C and NH₃-N (308.02 g and 12.71 g, respectively), minimal total C and N losses, and the highest bacterial population. Additionally, gaseous emission exhibited a strong correlation between physicochemical properties with intersection of 66.78% and a unique substrate utilizing bacterial communities. Consequently, the integrated application of biochar and bacterial consortium inoculation was suggested as an efficient method to adjust microbial activity and facilitate cellulose-rich waste degradation, enabling efficient management of organic waste from cow manure and wheat straw by composting.

Effect of pyrolysis temperature and correlation analysis on the yield and physicochemical properties of crop residue biochar

The aim of this study was to evaluate how pyrolysis temperature influences the yield and physicochemical properties of biochar. We produced biochar from four feedstocks (wheat straw, corn straw, rape straw, and rice straw) pyrolyzed at 300, 400, 500, and 600 °C for 1 h, respectively. The results showed that all biochar yields decreased consistently with increasing temperature during pyrolysis and showed a steady decrease over 400 °C. Rice straw derived biochar had high yield superiority due to its higher content of ash. Pyrolysis temperature has significant effects on the properties of biochar; demonstrating a negative relationship with H, O, H/C, O/C, (O + N)/C, and functional groups, whilst having a positive relationship with C, ash, pH, electrical conductivity, and surface roughness. Higher pyrolysis temperature was beneficial to the formation of a more recalcitrant constitutions and crystal structure, making it available for material application.

Biochar with near-neutral pH reduces ammonia volatilization and improves plant growth in a soil-plant system: A closed chamber experiment

Ammonia (NH₃) volatilization is considered as one of the major mechanisms responsible for the loss of nitrogen (N) from soil-plant systems worldwide. This study investigated the effect of biochar amendment to a calcareous soil (pH 7.8) on NH₃ volatilization and plant N uptake. In particular, the effect of biochar's feedstock and application rate on both NH₃ volatilization and plant growth were quantified using a specially designed closed chamber system. Two well-characterized biochars prepared from poultry manure (PM-BC) and green waste compost (GW-BC) were applied to the soil (0, 0.5, 1, 1.5 and 2% w/w equivalent to 0, 7.5, 15, 22 and 30 t ha^-1) and wheat (Triticum aestivum, variety: Calingiri) was grown for 30 days. Both PM-BC and GW-BC decreased NH₃ volatilization to a similar degree (by 47 and 38%, respectively), in the soil-plant system compared to the unamended control. Higher plant biomass production of up to 70% was obtained in the closed chamber systems with the addition of biochar. The increase in plant biomass was due to the reduction in N loss as NH₃ gas, thereby increasing the N supply to the plants. Plant N uptake was improved by as much as 58% with biochar addition when additional NPK nutrients were supplied to the soil. This study demonstrates that the application of biochars can mitigate NH₃ emission from calcareous agricultural cropping soil and that the retained N is plant-available and can improve wheat biomass yield.

Floating duckweed mitigated ammonia volatilization and increased grain yield and nitrogen use efficiency of rice in biochar amended paddy soils

Biochar (BC) potentially accelerates ammonia (NH₃) volatilization from rice paddy soils. In this regard, however, application the floating duckweed (FDW) to biochar-amended soil to control the NH₃ volatilization is not studied up-to-date. Therefore, the impacts of BC application with and without FDW on the NH₃ and nitrous oxide (N₂O) emissions, NUE and rice grain yield were evaluated in a soil columns experiment. We repacked soil columns with Hydragric Anthrosol and Haplic Acrisol treated in triplicates with Urea, Urea + BC and Urea + BC + FDW. Total NH₃ losses from Hydragric Anthrosol and Haplic Acrisol were 15.2-33.2 kg N ha^-1 and 19.6-39.7 kg N ha^-1, respectively. Urea + BC treatment recorded 25.6-43.7% higher (p < 0.05) NH₃ losses than Urea treatment, attributing to higher pH value of floodwater. Floating duckweed decreased soil pH and therefore significantly reduced (p < 0.05) the NH₃ volatilizations from the two soils by 50.6-54.2% over Urea + BC and by 34.2-38.0% over Urea treatment. Total N₂O emissions from Hydragric Anthrosol and Haplic Acrisol were 1.19-3.42 kg N ha^-1 and 0.67-2.08 kg N ha^-1, respectively. Urea + BC treatment increased N₂O emissions by 58.8-68.7% and Urea + BC + FDW treatment further increased N₂O emission by 187.4-210.4% over Urea treatment. Higher ammonium content of the topsoil, explained the N₂O increases in the Urea + BC and Urea + BC + FDW treatments. Urea + BC slightly reduced the rice grain yield and NUE, while the Urea + BC + FDW promoted both rice yield and NUE. Our data indicate that co-application of FDW along with BC in paddy soil could mitigate the NH₃ volatilization and enhance the rice grain yield and NUE.

A review on biochar modulated soil condition improvements and nutrient dynamics concerning crop yields: Pathways to climate change mitigation and global food security

The beneficial role of biochar on improvement of soil quality, C sequestration, and enhancing crop yield is widely reported. As such there is not much consolidated information available linking biochar modulated soil condition improvement and soil nutrient availability on crop yields. The present review paper addresses the above issues by compilation of world literature on biochar and a new dimension is introduced in this review by performing a meta-analysis of published data by using multivariate statistical analysis. Hence this review is a new in its kind and is useful to the broad spectrum of readers. Generally, alkalinity in biochar increases with increase in pyrolysis temperature and majority of the biochar is alkaline in nature except a few which are acidic. The N content in many biochar was reported to be more than 4% as well as less than 0.5%. Poultry litter biochar is a rich source of P (3.12%) and K (7.40%), while paper mill sludge biochar is higher in Ca content (31.1%) and swine solids biochar in Zn (49810 mg kg^-1), and Fe (74800 mg kg^-1) contents. The effect of biochar on enhancing soil pH was higher in Alfisol, Ferrosol and Acrisol. Soil application of biochar could on an average increase (78%), decrease (16%), or show no effect on crop yields under different soil types. Biochar produced at a lower pyrolysis temperature could deliver greater soil nutrient availabilities than that prepared at higher temperature. Principal component analysis (PCA) of available data shows an inverse relationship between [pyrolysis temperature and soil pH], and [biochar application rate and soil cation exchange capacity]. The PCA also suggests that the original soil properties and application rate strongly control crop yield stimulations via biochar amendments. Finally, biochar application shows net soil C gains while also serving for increased plant biomass production that strongly recommends biochar as a useful soil amendment. Therefore, the application of biochar to soils emerges as a 'win-win strategy' for sustainable waste management, climate change mitigation and food security.

Reducing ammonia volatilization from paddy field with rice straw derived biochar

Ammonia (NH₃) volatilization is a major loss of nitrogen fertilizer in paddy fields. The incorporation of straw or biochar has been considered to be the alternative options for soil improvement and agriculture sustainability. A field experiment was conducted to evaluate the potential role of rice straw and rice straw derived biochar in controlling NH₃ volatilization according to the conventional nitrogen fertilizer level (urea, 270 kg N ha^-1) during one rice (Oryza sativa L., cv. Xiushui134) growing season. Four treatments comprised rice straw at the rate of 8 t ha^-1 (RS); rice straw derived biochar at the rate of 2.8 t ha^-1 (RSBL); rice straw derived biochar at the rate of 22.5 t ha^-1 (RSBH) and a control (CK). Compared to straw application, biochar incorporation reduced the cumulative NH₃ volatilization (about 20%) from paddy fields significantly (p < 0.05), promoted rice yields and plant N aboveground as well as increased the abundance of ammonia oxidation amoA genes. In contrast with the control, the ratios of NH₃-N to total N input for RS, RSBL and RSBH declined significantly 4.15%, 4.40% and 11.12%, respectively (p < 0.05). Reduced NH₃ volatilization in RSB treatments were mainly attributed to the decrease of NH₄⁺-N concentration in the surface water, which could resulted from the enhancement of rice growth and the promotion of ammonia oxidation in soil. The increase of soil pH and soil CEC with biochar amendment played important roles in nitrogen retention and nitrogen cycle in soil. These results indicated that the incorporation of rice straw derived biochar instead of rice straw could be a promising approach to controlling NH₃ volatilization and improving rice yield.

Dynamics of fungal diversity and interactions with environmental elements in response to wheat straw biochar amended poultry manure composting

The fungal dynamics and its correlation with physicochemical and gaseous emission were investigated using metagenomics and Heat map illustrator (HEMI). Five different concentrations of wheat straw biochar (WSB) were applied to poultry manure (PM) and composted for 50 days; those without the WSB treatment were used as a control. The results revealed the dominant phyla to be Chytridiomycota, Mucoromycota, Ascomycota and Basidiomycota, while Batrachochytrium, Rhizophagus, Mucor, and Puccinia were the superior genera. In particular, the diversity of Chytridiomycota and Ascomycota was more abundant among all of the treatments. Overall, the diversity of the fungal species was correspondent, but relative abundance varied significantly among all of the composts. Principle Coordinate Analysis (PCoA) and Non-Metric Multi- Dimensional Scaling (NMDS) indicated that different concentrations of WSB applied treatments have significantly distinct fungal communities. In addition, correlation analyses of fungal interactions with environmental elements via HEMI also indicate a clear difference among the treatments. Ultimately, the relative abundance of fungal composition significantly influenced the PM compost treated by the WSB.