Biochar composites: Emerging trends,field successes and sustainability implications

Engineered biochars are promising candidates in a wide range of environmental applications, including soil fertility improvement, contaminant immobilization, wastewater treatment and in situ carbon sequestration. This review provides a systematic classification of these novel biochar composites and identifies the promising future trends in composite research and application. It is proposed that metals, minerals, layered double hydroxides, carbonaceous nanomaterials and microorganisms enhance the performances of biochars via distinct mechanisms. In this review, four novel trends are identified and assessed critically. Firstly, facile synthesis methods, in particular ball milling and co-pyrolysis, have emerged as popular composite fabrication strategies that are suitable for large-scale applications. Secondly, biochar modification with green materials, such as natural clay minerals and microorganisms, align well with the on-going green and sustainable remediation (GSR) movement. Furthermore, new applications in soil health improvement and climate change mitigation support the realization of United Nation's Sustainable Development Goals (SDGs). Finally, the importance of field studies is getting more attention, since evidence of field success is critically needed before large-scale applications.     

Effects of biochars derived from different feedstocks and pyrolysis temperatures on soil physical and hydraulic properties

Purpose

Biochar addition to soils potentially affects various soil properties, and these effects are dependent on biochars derived from different feedstock materials and pyrolysis processes. The objective of this study was to investigate the effects of amendment of different biochars on soil physical and hydraulic properties.

Materials and methods

Biochars were produced with dairy manure and woodchip at temperatures of 300, 500, and 700 °C, respectively. Each biochar was mixed at 5 % (w/w) with a forest soil, and the mixture was incubated for 180 days, during which soil physical and hydraulic properties were measured.

Results and discussion

Results showed that the biochar addition significantly enhanced the formation of soil macroaggregates at the early incubation time. The biochar application significantly reduced soil bulk density, increased the amount of soil organic matter, and stimulated microbial activity at the early incubation stage. Saturated hydraulic conductivities of the soil with biochars, especially produced at high pyrolysis temperature, were higher than those without biochars on the sampling days. The treatments with woodchip biochars resulted in higher saturated hydraulic conductivities than the dairy manure biochar treatments. Biochar applications improved water retention capacity, with stronger effects by biochars produced at higher pyrolysis temperatures. At the same suction, the soil with woodchip biochars possessed higher water content than that with the dairy manure biochars.

Conclusions

Biochar addition significantly affected the soil physical and hydraulic properties. The effects were different with biochars derived from different feedstock materials and pyrolysis temperatures.     

Designing relevant biochars as soil amendments using lignocellulosic-based and manure-based feedstocks

Purpose

Biochars are a by-product of the biofuel processing of lignocellulosic and manure feedstocks. Because biochars contain an assemblage of organic and inorganic compounds, they can be used as an amendment for C sequestration and soil quality improvement. However, not all biochars are viable soil amendments; this is because their physical and chemical properties vary due to feedstock elemental composition, biofuel processing, and particle size differences. Biochar could deliver a more effective service as a soil amendment if its chemistry was designed ex ante with characteristics that target specific soil quality issues. In this study, we demonstrate how biochars can be designed with relevant properties as successful soil amendments through feedstock selection, pyrolysis conditions, and particle size choices.

Materials and methods

Biochars were produced by pyrolysis of parent lignocellulosic feedstock sources—peanut hull (PH; Archis hypogaea), pecan shell (PS; Carya illinoensis), switchgrass (SG; Panicum virgatum), pine chips (PC; Pinus taeda), hardwood wastes (wood), and poultry litter manure (PL; Gallus domesticus), as well as blends of these feedstocks at temperatures ranging from 250 to 700 °C. Additionally, blended feedstocks were made into pellets (>2 mm) prior to pyrolysis at 350 °C. Dust-sized (<0.42 mm) biochar was obtained through grinding of pelletized biochars. After chemical characterization, the biochars were evaluated as fertility amendments in a Norfolk soil (fine-loamy, kaolinitic, thermic, Typic Kandiudult) during two different pot incubation experiments.

Results and discussion

PL biochars were alkaline and enriched in N and P, whereas biochar from lignocellulosic feedstocks exhibited mixed pH and nutrient contents. Blending PL with PC resulted in lower biochar pH values and nutrient contents. In pot experiment 1, most biochars significantly (P?<?0.05) raised soil pH, soil organic carbon, cation exchange capacity, and Mehlich 1 extractable P and K. PL biochar added at 20 g?kg^?1 resulted in excessive soil P concentrations (393 to 714 mg?kg^?1) and leachate enriched with dissolved phosphorus (DP, 22 to 70 mg?L^?1). In pot experiment 2, blended and pelletized PL with PC feedstock reduced soil pH and extractable soil P and K concentrations compared to pot experiment 1. Water leachate DP concentrations were significantly (P?<?0.05) reduced by pelletized biochar blends.

Conclusions

Short-term laboratory pot experiments revealed that biochars can have different impacts at modifying soil quality characteristics. Keying on these results allowed for creating designer biochars to address specific soil quality limitations. In the process of manufacturing designer biochars, first, it is important to know what soil quality characteristics are in need of change. Second, choices between feedstocks, blends of these feedstocks, and their accompanying particle sizes can be made prior to pyrolysis to create biochars tailored for addressing specific soil quality improvements. Utilization of these principles should allow for effective service of the designed biochar as a soil amendment while minimizing unwanted ex facto soil quality changes and environmental effects.     

An overview on biochar production, its implications, and mechanisms of biochar-induced amelioration of soil and plant characteristics

The degradation of soil fertility and quality due to rapid industrialization and human activities has stimulated interest in the rehabilitation of low-fertility soils to sustainably improve crop yield. In this regard, biochar has emerged as an effective multi-beneficial additive that can be used as a medium for the amelioration of soil properties and plant growth. The current review highlights the methods and conditions for biochar production and the effects of pyrolysis temperature, feedstock type, and retention time on the physicochemical properties of biochar. We also discuss the impact of biochar as a soil amendment with respect to enhancing soil physical (e.g., surface area, porosity, ion exchange, and water-holding capacity) and chemical (e.g., pH, nutrient exchange,functional groups, and carbon sequestration) properties, improving the soil microbiome for increased plant nutrient uptake and growth, reducing greenhouse gas emissions, minimizing infectious diseases in plants, and facilitating the remediation of heavy metal-contaminated soils. The possible mechanisms for biochar-induced amelioration of soil and plant characteristics are also described, and we consider the challenges associated with biochar utilization. The findings discussed in this review support the feasibility of expending the application of biochar to improve degraded soils in industrial and saline-alkali regions, thereby increasing the usable amount of cultivated soil. Future research should include long-term field experiments and studies on biochar production and environmental risk management to optimize biochar performance for specific soil remediation purposes.     

Effects of pyrolysis temperature and feedstock type on biochar characteristics pertinent to soil carbon and soil health: A meta-analysis

Biochar amendment to soil is utilized globally as an approach to enhance carbon storage and to improve soil functioning. However, biochar characteristics and related improvements of soil functioning depend on biochar production conditions. Systematic evaluation of corresponding biochar characteristics is needed for more targeted and efficient biochar application strategies. Herein, we systematically review the effects of biochar pyrolysis temperature (175–950°C) and feedstock (corn stover, switchgrass and wood) on selected biochar characteristics (carbon content, H/C ratio, nitrogen content, pH, specific surface area, ash content and pore volume). These specific characteristics were selected as being pertinent to soil organic carbon sequestration and soil health improvement. Despite numerous studies on these topics, few have numerically quantified the effects of pyrolysis temperature. Our results show that high pyrolysis temperature (>500°C) increased carbon content and pore volume for wood biochar compared with low pyrolysis temperature (≤500°C). The high pyrolysis temperature decreased the H/C ratio and nitrogen content but increased pH, specific surface area and ash content regardless of feedstock. Compared with corn stover biochar and switchgrass biochar, wood biochar had higher carbon content and larger specific surface area but lower nitrogen and ash contents regardless of pyrolysis temperature. The higher biochar carbon content might be derived from higher lignin and cellulose contents of wood feedstock. Wood feedstock had 76%–109% more lignin and 27%–47% more cellulose than corn stover and switchgrass. Corn stover biochar had higher pH, and switchgrass biochar had larger pore volume than wood biochar. Our study indicates that the targeted production of biochar with specific characteristics can be facilitated by the selection of pyrolysis temperature and feedstock type. For amending soil with biochar, more operationally defined biochar production conditions and feedstock selection might be a way forward to wider acceptance and better predictability of biochar performance under field conditions.     

生物质炭修复重金属及有机物污染土壤的研究进展

生物质炭是生物质原料在完全或部分缺氧条件下高温热解后的固体产物,它具有丰富的孔隙结构和较高的碳含量。该物质具有巨大的表面积和较强的阳离子交换能力等特殊性质,对受污染土壤中的重金属和有机物都具有很强的吸附能力,有效地降低这些污染物的生物有效性和在环境中的迁移,对改善土壤环境具有重大意义。近年来我国土壤污染严重,利用生物质炭修复受污染土壤的技术得到了广泛的关注。本文简述了生物质炭修复土壤污染的基本原理,探讨了与其他修复方法相比存在的优势,阐述了国内外近年来利用生物质炭修复污染土壤的研究进展,最后展望了今后需要进一步研究的领域。     

Effects of biochars produced from different feedstocks on soil properties and sunflower growth

The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic‐C‐poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat‐straw and olive‐tree‐pruning biochars), available P (wheat‐straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar‐application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash‐rich biochars (produced from wheat straw and olive‐tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.     

Sorption and desorption of phosphate on biochar and biochar–soil mixtures

The term biochar refers to materials with diverse chemical, physical and physicochemical characteristics that have potential as a soil amendment. The purpose of this study was to investigate the P sorption/desorption properties of various slow biochars and one fast pyrolysis biochar and to determine how a fast pyrolysis biochar influences these properties in a degraded tropical soil. The fast pyrolysis biochar was a mixture of three separate biochars: sawdust, elephant grass and sugar cane leaves. Three other biochars were made by slow pyrolysis from three Amazonian tree species (Lacre, Ingá and Embaúba) at three temperatures of formation (400 °C, 500 °C, 600 °C). Inorganic P was added to develop sorption curves and then desorbed to develop desorption curves for all biochar situations. For the slow pyrolysis, the 600 ºC biochar had a reduced capacity to sorb P (4–10 times less) relative to those biochars formed at 400 °C and 500 °C. Conversely, biochar from Ingá desorbed the most P. The fast pyrolysis biochar, when mixed with degraded tropical mineral soil, decreased the soil's P sorption capacity by 55% presumably because of the high soluble, inorganic P prevalent in this biochar (909 mg P/kg of biochar). Phosphorus desorption from the fast pyrolysis biochar/soil mixture not only exhibited a common desorption curve but also buffered the soil solution at a value of ca. 0.2 mg/L. This study shows the diversity in P chemistry that can be expected when biochar is a soil amendment and suggests the potential to develop biochars with properties to meet specific objectives.     

Influence of pyrolysis temperature on biochar property and function as a heavy metal sorbent in soil

While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood?cottonseed hull≈grass≈pine needle?broiler litter. To examine how biochar properties translate into its function as a heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to the surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.     

不同来源生物质废弃物热解炭化农业应用潜力分析:生物质炭产率、性质及促生效应

  【目的】  中国农业生物质废弃物种类多、数量大,且存在病原菌、农药和抗生素残留等潜在生态和环境风险。热解炭化作为一种废弃物的安全处理方法,其生物质炭的循环得率、性质及其土壤改良和促进作物生长的效应还需系统的比较研究。  【方法】  本研究选取作物生产来源的原生生物质、养殖业来源的次生生物质、食品加工处理的残余生物质等共26种生物质废弃物原料,在同一条件下炭化,分析不同来源原料热解后生物质炭产出率与性质。以小白菜 (Brassica campestris L. ssp.) 为试材进行盆栽试验,研究生物质炭对作物生长及土壤改良效应,进而评估这些废弃物炭化农业循环的应用潜力。  【结果】  供试26种废弃物炭化后的生物质炭产出率介于22%～71%,有机碳循环回收率介于22%～81%,氮素循环回收率介于21%～67%。26种废弃物生物质炭的pH和阳离子交换量差异较小 (变异系数10%左右),总有机碳、氮、水分、灰分含量等差异较大,变异系数在60%～70%;而不同原料生物质炭的电导率和溶解性有机碳含量变化极大,变异系数大于90%。生物质炭盆栽试验中,生物炭添加1%,小白菜生物量提升效应介于–34%～314%,变异系数大于100%;小白菜品质提升效应介于–14%～228%,变异系数为59%;土壤肥力提升效应介于20%～360%,特别是土壤有效磷含量提升幅度在0～24倍,均值为359%。同时,生物质炭产出率与生物质炭中灰分呈显著正相关,生物质炭的碳氮回收率与原料中碳氮含量呈显著正相关;不同原料热解炭化的质量回收率、碳氮回收率与小白菜产量及品质等指标间变化差异较大,在小白菜产量效应和品质效应间,部分生物质炭存在抵消作用,而另一部分生物质炭表现为协同作用。  【结论】  综合考虑热解炭化的生物质炭化循环率及碳氮回收循环率和土壤质量–植物生长协同提升效应,供试26种原料中,蚕砂、稻壳牛粪、骨粉、双孢菇渣、兔粪、羊粪和玉米渣的炭化循环率和土壤质量–植物生长协同提升幅度较高 (> 50%),为优先炭化农业利用的生物质废弃物;而木糖渣、稻壳粉、椰渣、高粱酒渣、核桃皮、蚓粪和红茶渣等废弃物热解炭化,因炭化循环率较低,或者土壤质量–植物生长提升的不一致效应,认为不宜炭化农业利用;而其余废弃物热解炭化后的效应介于上述两类之间,具有较高的炭化循环率和一定程度的土壤质量–植物生长协同提升效应,属于可炭化农业利用的生物质废弃物。     

Physicochemical Characteristics of Biochars Derived From Corn,Hardwood, Miscanthus,and Horse Manure Biomasses

Biochar, a carbon-rich by-product of biomass pyrolysis, is widely recognized as a potential ingredient for soil amendment, fertility, and carbon sequestration owing to its favorable physicochemical properties. The objective of this study was to investigate the chemical and physical properties of biochars produced through pyrolysis at 450°C from agricultural residues available in Northwest Missouri, namely hardwood (HW), corn stover (CR), miscanthus (MS), and horse manure (HM). These properties were assessed through the analysis of pyrolysis yield, pH, volatile matter, fixed carbon, ash and carbon (C), hydrogen (H), sulfur (S), nitrogen (N) contents, trace metal concentrations, surface morphology, surface functional groups, bulk density, and water holding capacity. The biochars derived from HW, MS and CR materials showed high volatile-matter (33–42%), high fixed carbon contents (42–47%), very low ash contents (6–15%), and low bulk density (0.14–0.28 g cm^?3) as compared to that of HM. A wide range of trace elements was observed in biochar samples with significant differences in concentrations. In addition, CR, HW and MS biochars displayed a disordered graphitic-like structure with well-developed pores and surface areas of 23, 70 and 90 m²/g respectively, and high water-holding capacity up to 750%, indicating their potential application as a soil amendment.     

Effects of pyrolysis temperature and residence time on physicochemical properties of different biochar types

Here we selected eight types of feedstocks to assess the effects of pyrolysis temperature (300°C, 400°C, 500°C and 600°C) and residence time (0.5, 1, 2, 4, 8 and 24 h), respectively, on the physicochemical properties. The fixed-carbon content, pH value and amount of basic functional groups in biochars increased as the pyrolysis temperature increased from 300°C to 600°C; the opposite trend was found in the biochar yield, adsorption capacity and amount of acidic functional groups. Increasing the residence time at low pyrolysis temperature (300°C) resulted in a gradual reduction in the biochar yield and progressive increase in the pH and iodine adsorption number of biochars. However, increasing the residence time at high pyrolysis temperature (600°C) had little effect on the biochar yield or pH, while it decreased the iodine adsorption number of biochars. Given the effects of pyrolysis conditions on the pH and iodine adsorption number of biochars, low-ash agricultural wastes (e.g. wheat straw) can be pyrolysed at 300°C, 2 h to produce biochar for improving alkaline soils; high-ash agricultural wastes (e.g. sweet potato vine) and forest litter (e.g. fresh leaves of apricot tree) are preferably pyrolysed at 300°C, 4 h to produce biochar for use in acidic soils.     

The potential feasibility for soil improvement, based on the properties of biochars pyrolyzed from different feedstocks

Purpose

Biochars have been considered as useful soil amendments due to their beneficial properties in improving soil fertility, carbon (C) sequestration, and soil decontamination. In our study, a series of biochars produced from different types of feedstocks at two pyrolysis temperatures (300 and 500 °C) were characterized to evaluate their different potentials as soil amendments.

Materials and methods

Ten types of feedstocks were used to prepare biochars at the pyrolysis temperatures of 300 and 500 °C, for 2 h. Chemical and physical analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier Transform Infrared (FTIR) analyses were conducted to determine differences in biochar properties. Then, soil incubation studies were used to investigate the relationships between these biochar properties and their different ameliorant values in soil.

Results and discussion

The pH, ash, total C, total potassium, total phosphorus, total base cation concentrations, surface areas, and total pore volumes of biochars produced at 500 °C were higher than at 300 °C, while the reverse applied for yields, total oxygen and total hydrogen, and average pore widths and particle sizes. Cluster analysis suggested that biochars derived from similar feedstock types belonged in the same category. The SEM, XRD, and FTIR analyses of typical biochars from the different categories suggested both variations and similarities in their characteristics. In addition, the results from soil incubation experiments were consistent with the conclusions made from biochar characteristics analysis.

Conclusions

Biochars derived from swine manures, fruit peels, and leaves with high pH and macro-nutrients appeared appropriate to increase soil pH and soil nutrient availability; whereas, biochars from wetland plant residues with high C concentrations and Brunauer–Emmett–Teller were better for soil C sequestration and contaminant adsorption.     

The importance of biochar quality and pyrolysis yield for soil carbon sequestration in practice

Biochar is a carbon (C)-rich material produced from biomass by anoxic or oxygen-limited thermal treatment known as pyrolysis. Despite substantial gaseous losses of C during pyrolysis, incorporating biochar in soil has been suggested as an effective long-term option to sequester CO₂ for climate change mitigation, due to the intrinsic stability of biochar C. However, no universally applicable approach that combines biochar quality and pyrolysis yield into an overall metric of C sequestration efficiency has been suggested yet. To ensure safe environmental use of biochar in agricultural soils, the International Biochar Initiative and the European Biochar Certificate have developed guidelines on biochar quality. In both guidelines, the hydrogen-to-organic C (H/C_org) ratio is an important quality criterion widely used as a proxy of biochar stability, which has been recognized also in the new EU regulation 2021/2088. Here, we evaluate the biochar C sequestration efficiency from published data that comply with the biochar quality criteria in the above guidelines, which may regulate future large-scale field application in practice. The sequestration efficiency is calculated from the fraction of biochar C remaining in soil after 100 years (F_perm) and the C-yield of various feedstocks pyrolyzed at different temperatures. Both parameters are expressed as a function of H/C_org. Combining these two metrics is relevant for assessing the mitigation potential of the biochar economy. We find that the C sequestration efficiency for stable biochar is in the range of 25%–50% of feedstock C. It depends on the type of feedstock and is in general a non-linear function of H/C_org. We suggest that for plant-based feedstock, biochar production that achieves H/C_org of 0.38–0.44, corresponding to pyrolysis temperatures of 500–550°C, is the most efficient in terms of soil carbon sequestration. Such biochars reveal an average sequestration efficiency of 41.4% (±4.5%) over 100 years.     

Biochar-induced changes in soil properties affected immobilization/mobilization of metals/metalloids in contaminated soils

Purpose

Remediation of metal contaminated soil with biochar is attracting extensive interest in recent years. Understanding the significance of variable biochar properties and soil types helps elucidating the meticulous roles of biochar in immobilizing/mobilizing metals/metalloids in contaminated soils.

Materials and methods

Six biochars were produced from widely available agricultural wastes (i.e., soybean stover, peanut shells and pine needles) at two pyrolysis temperatures of 300 and 700 °C, respectively. The Pb-, Cu-, and Sb-contaminated shooting range soils and Pb-, Zn-, and As-contaminated agricultural soils were amended with the produced biochars. The mobility of metals/metalloids was assessed by the standard batch leaching test, principal component analysis and speciation modeling.

Results and discussion

The changes in soil properties were correlated to feedstock types and pyrolysis temperatures of biochars based on the principal component analysis. Biochars produced at 300 °C were more efficient in decreasing Pb and Cu mobility (>93 %) in alkaline shooting range soil via surface complexation with carboxyl groups and Fe-/Al-minerals of biochars as well as metal-phosphates precipitation. By contrast, biochars produced at 700 °C outperformed their counterparts in decreasing Pb and Zn mobility (100 %) in acidic agricultural soil by metal-hydroxides precipitation due to biochar-induced pH increase. However, Sb and As mobility in both soils was unfavorably increased by biochar amendment, possibly due to the enhanced electrostatic repulsion and competition with phosphate.

Conclusions

It is noteworthy that the application of biochars is not equally effective in immobilizing metals or mobilizing metalloids in different soils. We should apply biochar to multi-metal contaminated soil with great caution and tailor biochar production for achieving desired outcome and avoiding adverse impact on soil ecosystem.

     

生物炭颗粒在饱和多孔介质中的迁移与滞留

生物炭在实际生产实践中具有许多潜在的农业和环境效益,因此受到了越来越多的关注。生物炭在多孔介质中的迁移不仅会影响它在土壤中的归趋,还可能会影响微生物群体及土壤有机质的动态变化以及被吸附的污染物对环境的影响。实验通过柱实验研究了微米级生物炭颗粒在饱和多孔介质中的迁移和滞留特性,主要选取了四种影响生物炭迁移的潜在因素:原材料、裂解温度、背景溶液pH值和离子强度。实验结果显示微米级生物炭在饱和多孔介质中具有一定的迁移能力,但是大部分的微米级生物炭会滞留在饱和多孔介质的表面和孔隙间。生物炭的制备原材料对于生物炭的表面电势特性有较大影响,从而影响了微米级生物炭在饱和多孔介质中的迁移能力。热解温度越高,生物炭的表面电势越大,迁移能力越弱。随着背景溶液离子强度增加和pH值减小,微米级生物炭颗粒在多孔介质中滞留增加,迁移能力减弱。     

Characterization of biochar and their influence on microbial activities and potassium availability in an acid soil

Application of biochar to soil has increased considerably during recent years because of its effectiveness as a soil amendment causing beneficial effects on soil health. However, the effects have been reported to vary and depend upon types of feedstock and pyrolysis conditions during biochar production. Therefore, characterization of biochar is extremely important for its efficient utilization as a soil amendment. In the present study, biochar was prepared from agro-industrial by-products (rice husk and sugarcane bagasse) and weeds (Parthenium and Lantana) under similar pyrolysis conditions. Lantana biochar (LBC) showed the highest pH (10.4) while the lowest value (8.5) being recorded in rice husk biochar (RHBC). The energy-dispersive X-ray spectroscopy (EDS) analysis indicated that LBC and Parthenium biochar (PBC) were superior with respect to potassium (K) content than sugarcane bagasse biochar (SBBC) and RHBC. The Fourier-Transform Infrared Spectroscopy (FTIR) study exhibited the existence of different functional groups in biochar. All the biochar treated soils showed significantly higher microbial activities with different degrees. Application of LBC and PBC at 4.50 g kg^?1 soil significantly increased K availability in soil. Lantana biochar and PBC amended the soil at 9 g kg^?1 significantly increased the soil pH thus makes these biochar as potential liming materials.     

Biochars influence sweet‐potato yield and nutrient uptake in tropical Papua New Guinea

Currently, the biomass of an invasive and obnoxious weed, kunai grass (Imperata cylindrica), is uncontrollably burnt in Papua New Guinea in subsistence farming systems resulting in unwarranted negative environmental consequences. We explored the possibility of sustainable utilization of biochar produced from the weed biomass along with a standard feedstock‐rice husk (Oryza sativa). Biochars were produced with lab‐scale pyrolysis at 550°C, characterized for chemical properties and plant nutrient composition. Further, agronomic efficacy of soil incorporation of biochars (5 t ha^?1) or co‐applied with mineral fertilizers (100, 11, and 62 kg ha^?1 N, P, K, respectively) was tested for sweet potato (Ipomoea batatas L. Lam) in a field experiment. The two biochars differed significantly (P < 5%) with respect to recovery from the feedstocks, chemical characters and nutrient composition. Kunai grass biochar was poorer in nutrients (< 1%) with distinctly alkaline pH and higher electrical conductivity. Biochar amendment to soil showed significant (P < 5%) improvement of soil moisture, while co‐application of biochars along with mineral fertilizers showed soil moisture decrease. Biochar amendment improved the growth parameters and total tuber yield of sweet potato by about 20%, while co‐application with mineral fertilizers augmented total tuber yield by 100% and above‐ground biomass yields by > 75%. Besides, improving agronomic performance of sweet potato crop, co‐application of biochars with mineral fertilizers enhanced uptake of N, P, K, Ca, Mg, and S. Production and utilization of biochar in sweet‐potato production could offer an efficient means of disposing biomass of kunai grass with concomitant productivity improvement in Papua New Guinea.     

不同生物炭对湿地松各组分生物量和碳储量的影响

通过将不同生物质原料(木屑和鸡粪)放置在低温(400°C)无氧条件下进行裂解,形成不同生物炭,研究了不同生物炭对湿地松不同组分(树叶、树皮、树枝和树干)生物量、碳密度、碳储量以及碳素年净固定量的影响。试验结果表明:以木屑和鸡粪为原料制备而成的两种生物炭p H和养分含量等性质差异显著;生物质裂解后,木屑p H由8.25降到木屑炭的7.46,而鸡粪炭p H为10.48,高于鸡粪的9.35;同时,C、N、P和K元素在两种生物炭中均出现富集,鸡粪生物炭N、P和K含量显著高于木屑生物炭,但两种生物炭速效P和速效K占总P、总K的比例与原料相比均出现显著降低。经过一年试验,鸡粪生物炭还田处理显著提高湿地松各个组分生物量,其中湿地松地上部分生物量增量是对照的4.92倍,而木屑炭处理对湿地松各个组分生物量影响不显著;木屑炭和鸡粪炭处理改变湿地松生物量增量在树叶和树皮中的分配比例,但对湿地松各个组分的碳密度影响不显著;鸡粪炭处理能显著提高湿地松各个组分碳素年净固定量,该处理湿地松地上部分碳素年净固定量(99.64 g/棵)分别是木屑炭处理(19.85 g/棵)和对照处理(25.77 g/棵)的5.02倍和3.87倍。由此可见,鸡粪炭可以作为提高林木土壤肥力的改良剂。     

生物炭对土壤肥力与环境质量的影响机制与风险解析

生物炭作为土壤改良剂和促进作物生长的应用价值已经被很多研究证实。该文综述了生物炭在改善农业土壤质量和作物生长中的应用研究进展,系统阐述了生物炭在提高农业土壤有效水含量,增加土壤矿质元素利用效率,缓解土壤酸化,降低土壤重金属生物有效性和提高农作物产量与质量方面的重要作用与微观机制。特别地,该文强调了生物炭应用于农业生态系统过程中可能引起的多环芳烃、重金属等污染物富集以及氮素根系吸收量下降等不可忽视的潜在问题,并对今后的重点研究方向进行了系统分析总结,以期为生物炭在提高土壤肥力质量与环境质量中的安全与高效利用提供科学参考。