Insight into modified biochars and their immobilizing effects on heavy metal(loid)s in contaminated soils: Mechanisms and influencing factors

Soil contamination by heavy metal(loid)s is a considerable environmental concern, and immobilization is a promising way to reduce toxicity. In recent years, modified/engineered biochars have gained enormous attention for their use in soil remediation, and various studies have reported notable results from their application and their ability to immobilize heavy metal(loid)s. In this review, a summary of publications on the utilization of modified biochars is presented to address the heavy metal(l...     

New trends in biochar pyrolysis and modification strategies: feedstock,pyrolysis conditions,sustainability concerns and implications for soil amendment

As a waste-derived soil amendment with a long history, biochar has received extensive attention for its capability to improve soil fertility/health; remove or immobilize contaminants in soil, water and air; and mitigate climate change. With the aim of producing engineered biochars with excellent performances, new trends in biochar pyrolytic production and modification strategies have emerged. This review critically summarizes novel pyrolysis methods (e.g., microwave-assisted pyrolysis, co-pyrolysis and wet pyrolysis) and modification approaches (e.g., mineral modification, photocatalytic modification, electrochemical modification) with a focus on (a) the mechanisms involved in environmental remediation processes including soil immobilization, contaminant adsorption and catalytic oxidation; (b) effects of feedstock and pyrolysis conditions on physicochemical properties; (c) sustainability considerations in novel modification and pyrolysis strategies; and (d) the feasibility of extrapolating the results from wastewater treatment to soil remediation. It is argued that in order to achieve the maximum net environmental benefits, ‘greener’ modification methods are warranted, and the risks associated with pyrolysis of contaminated feedstock in soil amendment and contaminant sorption can be minimized through various novel approaches (e.g., co-pyrolysis). Furthermore, novel pyrolysis methods can be combined with emerging modification strategies to synthesize more ‘effective’ biochars. Considering the similar aims of modification (e.g., increase surface area, introduce oxygen-containing functional groups, increase aromaticity), the applicability of several novel approaches could in future can be expanded from contaminant adsorption/degradation in aqueous media to soil remediation/fertility improvement.     

土壤微生物对不同粒径、不同表面和孔隙性质生物炭的响应

Biochars are known for their heterogeneity, especially in pore and surface structure associated with pyrolysis processes and sources of feedstocks. The surface area of biochar is likely to be an important determinant of the extent of soil microbial attachment, whereas the porous structure of biochar is expected to provide protection for soil microorganisms. Potential interactions between biochars from different sources and with different particle sizes were investigated in relation to soil microbial properties in a short-term incubation study. Three particle size(sieved) fractions(0.5–1.0, 1.0–2.0 and 2.0–4.0 mm) from three woody biochars produced from jarrah wood,jarrah and wandoo wood and Australian wattle branches, respectively, were incubated in soil at 25?C for 56 d. Observation by scanning electron microscopy(SEM) and characterisation of pore and surface area showed that all three woody biochars provided potential habitats for soil microorganisms due to their high porosity and surface areas. The biochars were structurally heterogeneous,varying in porosity and surface structure both within and between the biochar sources. After the 56-d incubation, hyphal colonisation was observed on biochar surfaces and in larger biochar pores. Soil clumping occurred on biochar particles, cementing and covering exposed biochar pores. This may have altered surface area and pore availability for microbial colonisation. Transient changes in soil microbial biomass, without a consistent trend, were observed among biochars during the 56-d incubation.     

Biochar effects on soil biota - A review

Soil amendment with biochar is evaluated globally as a means to improve soil fertility and to mitigate climate change. However, the effects of biochar on soil biota have received much less attention than its effects on soil chemical properties. A review of the literature reveals a significant number of early studies on biochar-type materials as soil amendments either for managing pathogens, as inoculant carriers or for manipulative experiments to sorb signaling compounds or toxins. However, no studies exist in the soil biology literature that recognize the observed large variations of biochar physico-chemical properties. This shortcoming has hampered insight into mechanisms by which biochar influences soil microorganisms, fauna and plant roots. Additional factors limiting meaningful interpretation of many datasets are the clearly demonstrated sorption properties that interfere with standard extraction procedures for soil microbial biomass or enzyme assays, and the confounding effects of varying amounts of minerals. In most studies, microbial biomass has been found to increase as a result of biochar additions, with significant changes in microbial community composition and enzyme activities that may explain biogeochemical effects of biochar on element cycles, plant pathogens, and crop growth. Yet, very little is known about the mechanisms through which biochar affects microbial abundance and community composition. The effects of biochar on soil fauna are even less understood than its effects on microorganisms, apart from several notable studies on earthworms. It is clear, however, that sorption phenomena, pH and physical properties of biochars such as pore structure, surface area and mineral matter play important roles in determining how different biochars affect soil biota. Observations on microbial dynamics lead to the conclusion of a possible improved resource use due to co-location of various resources in and around biochars. Sorption and thereby inactivation of growth-inhibiting substances likely plays a role for increased abundance of soil biota. No evidence exists so far for direct negative effects of biochars on plant roots. Occasionally observed decreases in abundance of mycorrhizal fungi are likely caused by concomitant increases in nutrient availability, reducing the need for symbionts. In the short term, the release of a variety of organic molecules from fresh biochar may in some cases be responsible for increases or decreases in abundance and activity of soil biota. A road map for future biochar research must include a systematic appreciation of different biochar-types and basic manipulative experiments that unambiguously identify the interactions between biochar and soil biota.     

玉米秸秆和污泥共热解制备的生物质炭及其对盐碱土壤理化性质的影响

[目的]研究不同温度制备的玉米秸秆和污泥基生物质炭不同施加量对盐碱土壤基本理化性质的影响,为盐碱土改良及土壤污染物质的生态修复等方面的研究提供科学依据。[方法]以质量比5∶2的玉米秸秆和剩余活性污泥为原料,分别在300,350,400,450,500℃共5个不同温度条件下热解制备生物质炭,通过扫描电镜、元素分析和红外光谱对其性质及结构进行分析,并通过培养试验研究其对盐碱土壤基本理化性质的影响。[结果]随着热解温度的升高,生物质炭微观结构越发达,比表面积越大,表面官能团的种类和数量也产生了显著性变化;同时随着热解温度逐渐升高,生物质炭C含量不断增加,而O,H和N含量却逐渐降低;添加玉米秸秆和污泥共热解制备的生物质炭能够显著增加盐碱土壤中有机碳含量,而土壤中总氮、总磷、有效磷、速效钾含量变化幅度较小;水溶性盐含量降低明显;加入生物质炭后大幅度提高了土壤阳离子交换能力,添加量越大,阳离子交换量越大;但生物质炭对土壤pH值影响不大。[结论]玉米秸秆和污泥基生物质炭提高了土壤养分含量和肥力指标,降低了土壤盐碱性。玉米秸秆和污泥基生物质炭可用于盐碱土壤的改良。     

生物质炭土壤调理剂的研究进展

生物质炭作为一种高效、绿色、多功能的土壤调理剂在农业生产和环境修复中具有广阔的应用前景,因而受到了国内外研究学者的广泛关注。论文综述了生物质炭在土壤改良、污染土壤修复、土壤微生物以及对农作物的影响机理等方面的研究成果,分析展望了生物质炭土壤调理剂的发展趋势,提出了需要进一步研究和解决的问题。     

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。     

生物质炭对连作参地土壤肥力及微生物特性的影响

为分析生物质炭用于老参地土壤修复的可行性,本研究采用Biolog、高通量测序等技术研究了3种生物质炭对连作参地人参品质、土壤肥力、微生物群落结构与功能多样性变化的影响。结果显示,增施不同生物质炭均有助于两年生重茬人参生物量及总皂苷含量的积累。结合生物质炭对土壤性质的影响研究结果发现,不同生物质炭对土壤有效磷、有机碳含量具有稳定的提升效果,增幅分别为47.04%~237.73%、8.09%~38.71%。增施生物质炭促进了土壤微生物的代谢活性,增加了土壤对聚合物类、酚酸类、氨基酸类、羧酸类碳源的利用效率,其中以酚酸类物质为底物的功能微生物种群数量显著增加。高通量测序结果显示,老参地土壤细菌物种数、丰度与多样性均呈下降趋势,细菌优势门类减少,单个门类优势度上升。生物质炭处理下土壤中细菌丰度与多样性增加,调控了变形菌门、厚壁菌门、疣微菌门、芽单胞菌门的优势度,使其数量变化趋势趋向于新林土。上述分析表明,重茬人参生物量和品质的提高与生物质炭提升土壤中人参生长的关键肥力指标,促进微生物代谢,调控细菌群落结构变化趋势有关。综上,生物质炭对老参地土壤表现出良好的修复、改良作用,适量增施生物质炭有利于老参地土壤质量的调节与恢复。     

生物质炭中的污染物含量及其田间施用的环境风险预测

生物质炭在碳固定、污染修复和酸性土壤改良中的应用非常广泛,但对生物质炭中所含污染物的研究甚少,其在田间应用中的环境风险并不清楚。该文选择松针和麦秆为原料,采用不同制备方法,研究了不同条件下获得的生物质炭中的重金属和多环芳烃含量,并初步评估了其田间应用的环境风险。研究表明,不同有机废弃物来源制备的生物质炭中均含有一定量的重金属(0.301～128mg/kg)和多环芳烃(1.48～5.48mg/kg);松针制备的生物质炭中的重金属含量普遍高于麦秆制备的生物质炭,而多环芳烃含量则相反,且高温制备有助于降低生物质炭中的多环芳烃含量;在低施用量的田间条件下,生物质炭的施用不易对土壤造成多环芳烃的环境风险,但在高施用量条件下,生物质炭中含有的多环芳烃容易使土壤中多环芳烃含量达到中度或重度污染的程度;生物质炭中的重金属在土壤中的积累量比较有限,环境风险较小。     

Application of Biochar and Compost for Enhancement of Rice (Oryza Sativa L.) Grain Yield in Calcareous Sandy Soil

The application of compost to calcareous soils by farmers is a well-established practice and has been shown to improve yields. However, incorporation of biochar and mixture of biochar and compost into calcareous soils is a relatively novel concept for improving soil quality and yield since calcareous soils comprise a large scale of soils worldwide. The objective of this study was to determine the effects of the co-application of biochar and compost on the soil properties, nutrient status and grain yield of rice in calcareous sandy soil. The experiment was conducted in a factorial arrangement based on randomized complete block design with three replications. The compost application rates were 1% and 3% (w/w; compost/soil) and the applied rates of biochars (rice straw biochar, RSB; sugarcane bagasse biochar, SBB) were 0.3% and 0.9% (w/w; biochar/soil). The results showed that soil pH decreased with increasing application rates of either compost or biochars. However, soil EC was enhanced through increasing the application rates of compost and biochars. The co-application of biochar and compost improved soil total N and available P concentrations. The soil available K increased with increasing the rate of incorporated biochars and compost. An increase of soil available K was more predominate with the application of RSB than SBB. The RSB, also, added a considerable amount of silicon (Si) to the soil. The co-incorporation of biochars and compost enhanced soil available concentrations of Fe, Zn, Cu, and Mn as well. The RSB was more effective than the SBB in grain yield enhancement almost certainly due to a higher Si content in RSB. Furthermore, the concurrent application of biochars and compost increased grain yield more than applying them individually. A higher application rate of biochar and compost induced a higher grain yield. The co-application of highest rates of RSB (0.9%) and compost (3%) induced the highest grain yield (26.1 g/pot) among the treatments. The increase in yield compare to the control were 321% and 260% for 0.9% RSB + 3% compost and 0.9% SBB + 3% compost, respectively. The increase in the grain yield was due to an improvement in the soil chemical properties and nutrients enhancement. Finally, the co-application of the highest rate of RSB (0.9%) and compost (3%) is recommended to obtain the appropriate rate of rice grain yield in calcareous sandy soil.     

Chemically and biologically activated biochars slow down urea hydrolysis and improve nitrogen use efficiency

Biochar is considered a potential technology to enhance chemical fertilizer use efficiency through intensification of the interactions between nutrients and the functional groups on biochar surfaces. However, little is known about how the application of activated biochars mixed with urea influences nitrogen(N) mineralization and crop performance in paddy fields. Here, a sawdust-derived fresh biochar (FBC)(ca. 400?C) was activated chemically with 15%hydrogen peroxide and biologically with a nutri...     

铁铝土泥浆包覆与淬灭强化荔枝木炭化物的碳固存率

生物质炭作为一种富碳多孔材料,具有固碳、减污和培肥等多重功效。基于当前限氧高温热裂解制炭技术及炭改性方法,该研究以亚热带地区常见的荔枝木为原材料、选取铁铝土制成泥浆,通过泥浆包覆和淬灭实现生物质“自限氧”和“水”淬灭,探讨铁铝土泥浆在荔枝木炭化过程中的作用及其对炭质的影响机理。结果表明：铁铝土泥浆包覆和淬灭制得的荔枝木炭的碳含量和碳固存率最高,分别为83.5%和83.9%,较无包覆水淬灭炭品的碳含量和碳固存率提高了16.7和37.8个百分点。扫描电镜-能谱分析的结果表明,铁铝土泥浆包覆和淬灭生成的炭品的碳骨架结构规整且其表面有铁铝矿物负载。一方面,泥浆通过涂层包覆形成了包覆壳,以物理阻隔作用截留了碳（防止炭化物中的碳在持续燃烧中生成CO_X）;另一方面,铁铝矿物在高温热裂解过程中与炭化物结合,形成了矿质（Fe/Al）-碳质复合体,实现了碳固存。研究可为生物质炭的制备提供新的便捷、廉价的技术思路,以生物质就地炭化和应用的碳负排放方案助力碳中和。     

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.     

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.     

Forms and solubility of plant nutrient elements in tropical plant waste biochars

Thailand is an agriculture‐based country which produces large amounts of agricultural waste. Making biochar from this waste can reduce pollution, decrease costs of production, and increase C sequestration. The agronomic benefits of biochar are partly derived from the available plant nutrients in biochar. This study investigated the fertilizer value of biochars manufactured by slow pyrolysis. Pyrolysis temperature and feedstock type affect nutrient concentrations and nutrient element speciation in biochar. The physio‐chemical, mineralogical and structural properties of biochars made from 14 agriculture wastes (soybean cake, corncob, lemon peel, sugar palm fibre, durian shell, tamarind wood, coconut fibre, coconut shell, bamboo wood, rice husk, eucalyptus wood, oil palm fruit, coffee waste, and bagasse) were investigated. The plant nutrients in biochar mostly occurred in crystalline minerals which were present on the surface and inside the cell structure of biochar. Most biochars examined in this research contained calcite (CaCO₃). The presence in biochars of several K‐minerals [archerite (KH₂PO₄), chlorocalcite (KCaCl₃), kalicinite (KHCO₃), pyrocoproite (K₂MgP₂O₇), struvite‐K (KMgPO₄ · 6 H₂O), and sylvite (KCl)] encourages the use of biochar as a K‐fertilizer. Fibre, fruit and wood biochars contained considerable amounts of K, Ca, and P. Sugar palm and coconut fibres also contained high level of Na in halite. This study recommends the utilization of biochars manufactured from sugar palm fibre, coconut fibre, durian shell, and oil palm fruit as fertilizers. With their appreciable contents of plant nutrients in highly to moderately soluble compounds these biochars should be effective fertilizers, especially for use by organic farmers who cannot use any chemical fertilizers.     

Improvement of physical and hydraulic properties of desert soil with amendment of different biochars

Purpose

The objective of this study was to investigate the effects of amendment of different biochars on the physical and hydraulic properties of desert soil.

Materials and methods

Biochars were produced with woodchip, rice straw, and dairy manure at temperatures of 300 and 700 °C, respectively. Each biochar at 5% (w/w) was mixed with desert soil, and the mixtures were incubated for 120 days.

Results and discussion

The different biochar treatments greatly reduced soil bulk density and saturated hydraulic conductivity. Especially the rice straw biochar addition resulted in the lowest saturated hydraulic conductivities among the treatments. Biochar addition significantly increased water retention of desert soil at any suction. At the same suction and experimental time, the treatment with the rice straw biochar produced at the lower temperature resulted in higher water content than the other treatments. The biochar additions slightly enhanced formation of soil macro-aggregates in the early experimental time. However, the aggregate contents gradually decreased with time due to the lack of effective binding agents (e.g., soil organic matter and clay minerals).

Conclusions

The changes of hydraulic properties of desert soil were attributable to the biochar properties. The higher fine particle content, porosity, and surface hydrophilicity of rice straw biochars were the most beneficial properties to increase soil water retention and to reduce water flow in the desert soil. The improvement of hydraulic properties by biochar addition may provide a potential solution to combat desertification.

     

生物炭对东北黑土持水特性的影响

为探究生物炭对东北黑土持水特性的影响,系统研究3种添加比例(2%、5%、10%)、3种粒径(0.25、0.5、1 mm)的杨木炭和竹炭对3种质地东北黑土(壤土、砂壤土、砂土)田间持水量和含水率的影响规律,构建添加生物炭黑土的水分特征曲线,并采用Van-Genuchten和Broods-Corey模型进行拟合。结果表明:生物炭能显著提高不同质地东北黑土的持水能力,黑土的田间持水量与生物炭的添加比例呈显著正相关,而与生物炭的粒径呈负相关,0.5 mm和1 mm粒径的生物炭对黑土田间持水量的影响差异不显著,杨木炭显著优于竹炭,0.25 mm、10%添加比例的杨木炭对东北黑土持水能力的提高效果最优,壤土、砂壤土、砂土3种质地黑土的田间持水量和饱和含水率分别可提高64.97%、66.42%、69.39%和47.60%、38.93%、31.18%;Van-Genuchten模型能更精确的模拟添加生物炭黑土的水分特征曲线,最佳离心时间为100 min,三次函数曲线能够较好的拟合添加生物炭黑土的体积含水率与离心吸力之间的多元动态关系,为生物炭对各种质地东北黑土水分运动规律的深入研究提供理论依据。     

施用改良剂对皖南旱坡地土壤性状及烤烟产量和品质的综合效应

通过田间小区试验研究了无机矿石类及生物炭改良剂不同组合对皖南旱坡地土壤性状以及烤烟产量和烟叶品质的影响。结果表明:与对照相比,3种无机矿石材料(T20、G20、硅藻土)和2种生物炭(竹炭和砻糠炭)的改良剂的不同组合,可使土壤体积质量下降0.27~0.34 g/cm3,田间持水量提高11.6%~55.6%,pH提高了0.45~0.93个单位;烤烟产量增加26~397 kg/hm~2,烤烟烟碱与全氮含量有所下降,还原糖含量有所增加,糖碱比优化,品质进一步提升。本研究结果可以为皖南旱坡地烟区土壤改良、提高特色烟产量和品质、促进农民增产增收提供有效的指导。     

两种生物炭对污染土壤铜有效性的影响

采用盆栽试验,探究了添加不同比例(0,1%,2%,4%)玉米秸秆炭和商陆根生物炭对铜污染红壤中小油菜生长与铜有效性的影响。结果表明,与对照相比,添加两种生物炭均能够增加铜污染红壤上小油菜的生物量。在低铜污染水平下,4%玉米炭和商陆炭处理小油菜生物量分别增加了21.2倍和67.9倍;高铜污染水平下,4%玉米炭和商陆炭处理小油菜生物量分别增加了8.6倍和109.6倍。商陆炭的添加能够显著提高土壤p H值,在低铜污染水平下,商陆炭处理土壤p H值升高了0.4~1.66个单位,较玉米炭处理土壤p H值多升高了0.25~1.35个单位;在高铜污染下,商陆炭处理土壤p H值升高了0.33~1.52个单位,较玉米炭土壤p H值多升高了0.3~1.25个单位。向污染土壤中添加两种生物炭均能够显著降低土壤有效态铜的含量。其中,在低铜污染土壤中,4%玉米炭和商陆炭处理土壤有效态铜含量分别降低了21.9%和45.2%;在高铜污染土壤中,4%玉米炭和商陆炭处理土壤有效态铜含量分别降低了41.9%和53.8%。两种生物炭均能够显著降低小油菜铜累积量,向低铜污染土壤中添加4%的玉米炭和商陆炭,小油菜地上部铜含量下降了21.2%、67.8%。高污染土壤中添加4%的玉米炭和商陆炭小油菜地上部铜含量下降了19.9%、66.8%。两种生物炭均可以改良红壤的酸度,降低土壤铜有效性,并提高小油菜的生物量,降低小油菜铜累积量,但是商陆炭的效果更为明显。     

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.