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[hal-04369332] Editorial : Celebrating the work of Early Career Researchers in Soil Science
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ano.nymous@ccsd.cnrs.fr.invalid (Xavier Portell) 02 Jan 2024
https://hal.inrae.fr/hal-04369332
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[hal-04032123] Current controversies on mechanisms controlling soil carbon storage: implications for interactions with practitioners and policy-makers. A review
There is currently an intense debate about the potential for additional organic carbon storage in soil, the strategies by which it may be accomplished and what the actual benefits might be for agriculture and the climate. Controversy forms an essential part of the scientific process, but on the topic of soil carbon storage, it may confuse the agricultural community and the general public and may delay actions to fight climate change. In an attempt to shed light on this topic, the originality of this article lies in its intention to provide a balanced description of contradictory scientific opinions on soil carbon storage and to examine how the scientific community can support decision-making despite the controversy. In the first part, we review and attempt to reconcile conflicting views on the mechanisms controlling organic carbon dynamics in soil. We discuss the divergent opinions about chemical recalcitrance, the microbial or plant origin of persistent soil organic matter, the contribution of particulate organic matter to additional organic carbon storage in soil, and the spatial and energetic inaccessibility of soil organic matter to decomposers. In the second part, we examine the advantages and limitations of big data management and modeling, which are essential tools to link the latest scientific theories with the actions taken by stakeholders. Finally, we show how the analysis and discussion of controversies can guide scientists in supporting stakeholders for the design of (i) appropriate trade-offs for biomass use in agriculture and forestry and (ii) climate-smart management practices, keeping in mind their still unresolved effects on soil carbon storage.
ano.nymous@ccsd.cnrs.fr.invalid (Delphine Derrien) 17 Mar 2023
https://hal.inrae.fr/hal-04032123
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[hal-02958540] Can N$_2$O emissions offset the benefits from soil organic carbon storage?
To respect the Paris agreement targeting a limitation of global warming below 2°C by 2100, and possibly below 1.5°C, drastic reductions of greenhouse gas emissions are mandatory but not sufficient. Large‐scale deployment of other climate mitigation strategies are also necessary. Among these, increasing soil organic carbon (SOC) stocks is an important lever because carbon in soils can be stored for long periods and land management options to achieve this already exist and have been widely tested. However, agricultural soils are also an important source of nitrous oxide (N$_2$O), a powerful greenhouse gas, and increasing SOC may influence N$_2$O emissions, likely causing an increase in many cases, thus tending to offset the climate change benefit from increased SOC storage. Here, we review the main agricultural management options for increasing SOC stocks. We evaluate the amount of SOC that can be stored as well as resulting changes in N$_2$O emissions to better estimate the climate benefits of these management options. Based on quantitative data obtained from published meta‐analyses and from our current level of understanding, we conclude that the climate mitigation induced by increased SOC storage is generally overestimated if associated N$_2$O emissions are not considered but, with the exception of reduced tillage, is never fully offset. Some options (e.g, biochar or non‐pyrogenic C amendment application) may even decrease N$_2$O emissions.
ano.nymous@ccsd.cnrs.fr.invalid (Bertrand Guenet) 01 Jun 2022
https://hal.inrae.fr/hal-02958540
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[hal-03517541] Loïc Pagès, founding scientist in root ecology and modelling
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ano.nymous@ccsd.cnrs.fr.invalid (Jean-François Barczi) 24 May 2022
https://hal.inrae.fr/hal-03517541
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[hal-03106863] Bypass and hyperbole in soil science: A perspective from the next generation of soil scientists
We, the co‐authors of this letter, are an international group of soil scientists at early career stages, from PhD students to postdoctoral researchers, lecturers, and research fellows with permanent positions. Here, we present our collective musings on soil research challenges and opportunities and, in particular, the points raised by Philippe Baveye (Baveye, 2020a, 2020b) and Johan Bouma (Bouma, 2020) on bypass and hyperbole in soil science. Raising awareness about these issues is a first and necessary step. To this end, we would like to thank Philippe Baveye and Johan Bouma for initiating this debate........
ano.nymous@ccsd.cnrs.fr.invalid (Xavier Portell) 12 Jan 2021
https://hal.inrae.fr/hal-03106863
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[hal-02958549] Carbon, nitrogen and phosphorus release from peat and forest floor-based cover soils used during oil sands reclamation
Reclamation practices in the oil sands region of Alberta involve the reconstruction of soil profiles using a combination of salvaged mineral substrates and organic-matter-rich surface materials, including peat–mineral mix (PM) and forest floor – mineral mix (FFM). The successful re-establishment of vegetation on reclaimed sites is for a large part dependent on the nutrients these materials can provide. Hence, the overall objective of this study was to compare carbon (C), nitrogen (N), and phosphorus (P) release rates from PM and FFM materials used to cap reconstructed sandy soils. A 325 d laboratory incubation was conducted to measure these rates. The two materials released comparable amounts of N on a per kilogram of soil basis (111–118 mg N kg−1). However, when results were normalized based on each material’s organic C content, N release was six times greater for FFM than for PM, in accordance with results of previous studies. In addition, overall C mineralization and P release rates were over one order of magnitude higher with FFM than with PM. As opposed to N, however, P release seemed to be controlled more by abiotic processes than by organic matter mineralization. While the FFM material overall released more N and P, it also degraded faster; in comparison, PM may provide a smaller but more stable release of N.
ano.nymous@ccsd.cnrs.fr.invalid (Sylvie Quideau) 06 Oct 2020
https://hal.inrae.fr/hal-02958549
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[hal-02614587] Water and nutrient retention in coarse-textured soil profiles from the Athabasca oil sand region
Post-mining land reclamation of Athabasca Oil Sands (AB, Canada) involves the reconstruction of soil profiles able to support a mosaic of boreal forest communities. However, the use of coarse-textured reclamation materials to recreate forest ecosystems represents a challenge in terms of soil water and nutrient availability. This work aimed to quantify nutrient leaching in reclaimed coarse-textured soils constructed with two coversoils (peat mineral mix and forest floor mineral mix) underlain by mineral materials, including a blended B/C subsoil reclamation material, lean oil sand overburden substrate, and tailing sand. Water retention and conductivity curves were estimated for each material, and their retention capacity for inorganic N and P was measured in sorption isotherm experiments. The redistribution of water, inorganic N and P five days after an intense rain event was evaluated in six different reclaimed soil profiles using a laboratory-controlled leaching experiment in 1.2-m deep columns. The redistribution of fertilizer nutrients was also measured following the addition of 15N-labelled ammonium and phosphate over the top 10 cm of the columns. In addition, a 25-day incubation experiment with the two coversoils enabled us to estimate the timing of N immobilization and nitrification processes. Our results show that, depending on the combination of materials used for land reclamation, the soil profiles may provide equal or higher amounts of inorganic N and P in the rooting zone compared to natural, coarse-textured soils of the region. Following the simulated intense rainfall, the peat-mineral mix was able to retain 44% of its initial inorganic N within the top 20 cm of the reclaimed soil profiles, while 84% of the inorganic N present in the forest floor mineral mix was leached down. Compared to the movement of water, the leaching of N down the soil profiles was slower and partly restricted by the presence of lean oil sand, and to a lesser degree tailing sand. Most of the introduced fertilizer-N remained in the first 20 cm of the soil profiles under the form of nitrate, although the incubation experiment suggested that nitrification only occurred after the simulated rainfall event. Based on our experimental data and on additional simulations of water and nutrient transport, we conclude that nutrient leaching in reclaimed soils can be significant if specific materials such as forest floor mineral material and coarse-textured subsoil are combined and when an intense rainfall occurs at a period coinciding with a high concentration of nitrate-N in the topsoil.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 27 May 2020
https://hal.science/hal-02614587
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[hal-02614591] Microbial response to carbon and nutrient additions in boreal forest soils and coversoils used during post-mining reclamation
Two types of organic-matter-rich coversoils are used during reclamation in the oil sands region of Alberta: forest floor material (FFM) salvaged from upland forests, and peat material (PM) salvaged from boreal wetlands. In this study, we tested the hypothesis that carbon (C) and nutrient availability may limit microbial activity in these reclamation materials by measuring their response to either 13C-labeled glucose or NPKS addition. Coversoil materials were compared with two natural forest soils corresponding to target sites for reclamation. A shift in microbial community structure (determined using phospholipid fatty acid analysis) was detected after both additions, but it was stronger with glucose than NPKS, especially for the two reclamation materials. For all soils, the increase in microbial respiration was stronger after glucose than after NPKS addition. The majority of CO2 originated from soil organic matter (SOM) for the natural forest soils but from glucose for the reclamation materials. In PM, glucose addition triggered SOM mineralization, as shown by a positive priming effect. Despite the absence of a priming effect for FFM, microbial communities incorporated higher rates of glucose into their biomass and respired double the amount of glucose compared with the other materials. Furthermore, the overall microbial community structure in the FFM became more similar to that of the natural forest soil materials following glucose addition. These findings indicate that C and NPKS limitations were stronger for the two reclamation materials than for the two natural forest soils. Furthermore, microbial communities in the two reclamation materials responded more readily to labile C than to NPKS addition.
ano.nymous@ccsd.cnrs.fr.invalid (Justine Lejoly) 21 May 2020
https://hal.science/hal-02614591
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[hal-02614581] Biochar-assisted phytoextraction of Cd and Zn by Noccaea caerulescens on a contaminated soil: A four-year lysimeter study
Amendments of biochar, the residual solid of biomass pyrolysis, have been shown to enhance metal phytoextraction from contaminated soils with hyperaccumulating plants in specific situations. In order to investigate this phenomenon over successive harvests in field conditions, two identical undisturbed soil cylinders (1-m2 section × 1.85-m height) were excavated from a contaminated agricultural plot and monitored with instrumented lysimeters. Wood-derived biochar was added at a rate of 5% (w/w) in the first 30 cm of one of the two lysimeters. The Cd/Zn-hyperaccumulator Noccaea caerulescens was then grown for the next four years on both lysimeters. Our results showed that the hyperaccumulating plant was able to remove about 2 g m−2 of Cd and 12–16 g m−2 of Zn within four years, representing about 40% and 4% of the initial Cd and Zn soil contamination, respectively. Biochar amendment improved plant germination and survival and increased root surface density. However, no significant effect of biochar on shoot metal content of N. caerulescens was observed. Mass balances suggested that up to 10% the metal contamination moved from the disturbed Ap horizon to the deeper horizons, particularly in the biochar-amended soil profile. Furthermore, shoot Cd and Zn concentration generally decreased over the successive harvests, together with soil metal availability. Depending on the way to account for this progressive decrease in efficiency, our estimations of the time necessary to remove the excess of metals in the topsoil in these conditions ranged from 11 to 111 years for Cd and from 97 years to an infinite time for Zn. In conclusion, the simultaneous use of N. caerulescens and biochar amendment can lead to a significant removal of specific metallic elements from the topsoil, but the risk of metal movement down the soil profile and the observed decrease in phytoextraction efficiency over time deserve further investigations.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 21 May 2020
https://hal.science/hal-02614581
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[hal-02173903] Micropedology to reveal pedogenetic processes in Technosols
Technosols are characterized by the presence of mineral and organic parent materials of technogenic origin (e.g. agricultural or urban wastes, industrial by-products, building materials, transported natural materials). In view of the continual increase of such man-made soils, there is a true need of understanding their functioning and evolution. Micropedology, i.e. morphological and analytical characterization of pedofeatures on soil sections, appears as a relevant approach to take into account the diversity and the specificity of Technosols in the knowledge of their pedogenetic processes. Micropedology was investigated at microscopic and submicroscopic scale on four Technosols. Therefore, it determined specific features of anthropogenic constituents allowing in situ monitoring until the early stages of Technosol pedogenesis. Organic matter dynamics, soil porosity evolution, impact of faunal activity or hydric conditions on Technosol structure were investigated. Moreover, as Technosol components and deposition modes are diverse, one can expect numerous interfaces. In that way, micropedology appeared particularly well adapted to study these local interfaces as sites of favoured pedogenesis. Supplemented with overall physico-chemical soil analyses, characterization of Technosol pedogenic features using micropedology improves the understanding of their functioning and evolution. In addition, according to the environmental context, such data also give useful information for the Technosol management.
ano.nymous@ccsd.cnrs.fr.invalid (Françoise Watteau) 04 Jul 2019
https://hal.science/hal-02173903
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[hal-01934274] Storage of carbon in constructed technosols: in situ monitoring over a decade
Artificial soils constructed from wastes and by-products have been considered as a sustainable option for land reclamation. In particular, they could contribute in a complementary manner to natural soils to global climate regulation by storing large quantities of carbon (C). However, the evolution of C stocks in such newly formed soils remains largely unknown. This work aimed at evaluating the dynamics of C in constructed Technosols, focusing on two experimental sites in Lorraine, France, where Technosols were constructed from thermally-treated industrial soil, papermill sludge and green waste compost, and planted with grasses. Soil samples were collected over 12 years, and stocks of C were calculated, taking into account the increase in soil bulk density and the associated decrease in soil thickness over the years. The evolution of the stocks of organic C was compared to the evolution reported for natural grassland soils from the same region and for other Technosols. Initial organic C stocks in the two constructed Technosols were 50% higher than in natural analog soils when calculated over 30 cm, and up to 5 times higher when calculated over 100 cm. Organic C stocks in the two Technosols decreased over the first three years, but increased during the following years, most likely due to the accumulation of plant-derived C. A similar evolution was observed in other planted Technosols. We conclude that Technosols constructed from an adequate set of parent materials can keep large amounts of organic C over time and sequester additional C under permanent plant cover.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 25 Nov 2018
https://hal.univ-lorraine.fr/hal-01934274
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[hal-01934269] Phytoextraction of Ni from a toxic industrial sludge amended with biochar
Agromining is a technology based on the phytoextraction of metals by hyperaccumulator plants, combining agronomic and hydrometallurgical processes, to produce metal-based compounds. So far, it has been primarily developed to recover Ni from ultramafic soils, but secondary materials, namely industrial wastes containing Ni, may offer new opportunities for agromining. However, because of the toxicity of such materials, plants cannot be grown without formulating suitable substrates. The aim here was to assess the feasibility of growing Ni-hyperaccumulating plants on a Technosol containing a toxic industrial sludge and to test the influence of a biochar amendment on plant growth and Ni uptake. A constructed soil was prepared by mixing a decontaminated soil with an industrial sludge containing high concentrations of Fe, Ni, P and Zn, and amending it with biochar at different rates (0 to 5 wt%, dry matter). An ultramafic, Ni-rich soil was used as a reference material. Pot experiments were conducted with the hyperaccumulator Alyssum murale and the non-accumulating plant Lolium multiflorum used as a reference plant. After twelve weeks of growth, plant shoots and roots and soil samples were collected and analysed. Soil pore water was also collected over the experiment and analysed. Results showed that the growth of both plants was higher on the constructed soil than on the ultramafic soil, and increased with biochar amendments. The highest amounts of phytoextracted Ni were reached by A. murale on the ultramafic soil in the presence of biochar, whereas they remained low on the constructed soil. Contrary to the ultramafic soil, the constructed soil contained high amounts of Zn which was shown to impair Ni uptake as a result of the strong competition between Ni and Zn. Further investigations should therefore focus on practical solutions for decreasing this competition in order to maximize Ni uptake. In conclusion, agromining was proven feasible on soils constructed from industrial waste containing metals, providing that such soils are carefully designed to meet hyperaccumulator requirements
ano.nymous@ccsd.cnrs.fr.invalid (Marie Rue) 25 Nov 2018
https://hal.univ-lorraine.fr/hal-01934269
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[hal-01865610] Decrease in the genotoxicity of metal-contaminated soils with biochar amendments
Biochar amendments, i.e., the solid product of biomass pyrolysis, reduce soil metal availability, which may lower the toxicity of metal-contaminated soils. A direct link between the decrease in soil metal availability and improved plant development is however often difficult to establish, as biochar may induce undesirable side effects on plant growth, e.g., a modification to plant nutrition. In order to investigate toxicity processes at a cellular level, roots of Vicia faba were exposed for 7 days to three metal-contaminated substrates and one control soil, amended with a 0 or 5% (w/w) addition of a wood-derived biochar. Exposure to pure biochar was also tested. Root tip cells were then observed to count the number of micronuclei as an estimation of DNA damage and the number of cells at mitosis stage. Results showed that biochar amendments led to a significant decrease in soil metal availability (Cd, Cu, Ni, Pb, and Zn) and to enhance root development on acidic substrates. The micronucleus frequency in root tip cells was positively correlated and the number of mitotic cells negatively, to the extractability of Zn in soils and to the concentration of Zn in secondary roots. Exposure to pure biochar caused a lower production of roots than most soil substrates, but led to the lowest number of observed micronuclei. In conclusion, biochar amendments can reduce the genotoxicity associated with the presence of metallic contaminants in soils, thereby potentially improving plant growth.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 31 Aug 2018
https://hal.science/hal-01865610
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[hal-01699912] A novel process to recover cadmium and zinc from the hyperaccumulator plant Noccaea caerulescens
Soils contaminated with heavy metals represent a serious threat for humans and all ecosystems. In some cases, they can be remediated by metal phytoextraction, using accumulator or hyperaccumulator plants, however the fate of harvested metal-enriched biomass has to be addressed. Cadmium (Cd) and, zinc (Zn) are very common contaminants of urban, industrial and agricultural soils. To date, no process has been developed to recover these metals from plant biomass.This contribution presents a novel hydrometallurgical process designed to recover Cd and Zn from the biomass of a Zn/Cd hyperaccumulator plant Noccaea caerulescens. Dried plants are first ashed at 620 degrees C, a process which has been carefully investigated to avoid metal loss, and then the ash is acid leached. Following this, the process comprises two main steps: one to extract Cd and Zn and the other for Cd cementation using Zn powder and selective precipitation of Zn. Optimal cementation conditions have been determined with synthetic solutions using a Box-Behnken experimental design. In this context, a mole ratio Zn:Cd of 2:1, a temperature of 25 C and a duration of 50 min proved optimal. The full process was tested on a sample of plant biomass. It demonstrated that Cd and Zn recovery was possible by cementation and precipitation. This new process still has to be optimized and up-scaled but it paves the way to Cd and Zn recovery from diverse types of soils, and even to 'metal cultivation', an emergent phytoteclmology now referred to as agromining.
ano.nymous@ccsd.cnrs.fr.invalid (Claire Hazotte) 02 Feb 2018
https://hal.science/hal-01699912
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[hal-01611435] Biochars in soils: towards the required level of scientific understanding
Key priorities in biochar research for future guidance of sustainable policy development have been identified by expert assessment within the COST Action TD1107. The current level of scientific understanding (LOSU) regarding the consequences of biochar application to soil were explored. Five broad thematic areas of biochar research were addressed: soil biodiversity and ecotoxicology, soil organic matter and greenhouse gas (GHG) emissions, soil physical properties, nutrient cycles and crop production, and soil remediation. The highest future research priorities regarding biochar's effects in soils were: functional redundancy within soil microbial communities, bioavailability of biochar's contaminants to soil biota, soil organic matter stability, GHG emissions, soil formation, soil hydrology, nutrient cycling due to microbial priming as well as altered rhizosphere ecology, and soil pH buffering capacity. Methodological and other constraints to achieve the required LOSU are discussed and options for efficient progress of biochar research and sustainable application to soil are presented.
ano.nymous@ccsd.cnrs.fr.invalid (Priit Tammeorg) 05 Oct 2017
https://hal.science/hal-01611435
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[hal-01607260] Metal Immobilization on Wood-Derived Biochars: Distribution and Reactivity of Carbonate Phases
Metals can be immobilized on biochars by precipitation with carbonate. The distribution of metal-carbonate phases at the surface of biochars and the conditions of their formation, however, are unknown. Electron microscopy and X-photon spectroscopy were used to characterize carbonate phases in various morphological groups of particles of a wood-derived biochar, both before and after a metal-sorption experiment. Our results showed that the distribution of metals at the surface of biochar particles depended on the corresponding wood tissues and the presence of carbonate phases. Metals were particularly concentrated (i) within calcium carbonate crystals in bark-derived particles, which originated from calcium oxalate crystals formed prior to pyrolysis, and (ii) as new phases formed by the reprecipitation of carbonate on specific tissues of biochar. The formation of biochar carbonate phases and their redistribution by dissolution-precipitation mechanisms may primarily control the localization of metals on biochar particles and the durability of metals immobilization.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 03 Oct 2017
https://hal.science/hal-01607260
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[hal-01486423] Plant growth and metal uptake by a non-hyperaccumulating species (Lolium perenne) and a Cd-Zn hyperaccumulator (Noccaea caerulescens) in contaminated soils amended with biochar
Biochar could be used as a soil amendment in metal contaminated soils, for safe crop production or soil remediation purposes. This work was conducted to study the effects of biochar amendments on metal uptake by two contrasted plants grown on metal-contaminated soils. A non-hyperaccumulating plant (Lolium perenne) and a Cd- and Zn-hyperaccumulator (Noccea caerulescens) were grown in pots on acidic (A) and alkaline (B) soil contaminated by Cd, Pb and Zn, both amended by a wood-derived biochar. Biochar amendments decreased the availability of metals by increasing soil pH, but also decreased Ca, P and N availability. Growth of L. perenne was increased and shoot metal uptake decreased by biochar addition in both soils, although increasing biochar dose above 0.5 % resulted in a progressive decrease of shoot production on soil B. Growth of N. caerulescens was not significantly affected by biochar. But an increase of Cd uptake with 5 % biochar was recorded on both soils, and of Zn uptake on soil B. Beside immobilizing metals, biochar may decrease the availability of nutrients, leading either to plant deficiency or to a decreased competition with cations for metal uptake, thus enhancing extraction of metals by hyperaccumulators.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 09 Mar 2017
https://hal.science/hal-01486423
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[hal-01458427] Metal immobilization by sludge-derived biochar: roles of mineral oxides and carbonized organic compartment
Pyrolyzing sludge into biochar is a potentially promising recycling/disposal solution for municipal wastewater sludge, and the sludge-derived biochar (SDBC) presents an excellent sorbent for metal immobilization. As SDBC is composed of both mineral oxides and carbonized organic compartment, this study therefore compared the sorption behaviour of Pb and Zn on SDBC to those of individual and mixture of activated carbon (AC) and amorphous aluminium oxide (Al2O3). Batch experiments were conducted at 25 and 45 C, and the metal-loaded sorbents were artificially aged in the atmosphere for 1–60 days followed by additional sorption experiments. The Pb sorption was generally higher than Zn sorption, and the co-presence of Pb reduced Zn sorption on each studied sorbent. Higher sorption capacities were observed at 45 C than 25 C for SDBC and AC, while the opposite was shown for Al2O3, indicating the significance of temperaturedependent diffusion processes in SDBC and AC. Nevertheless, metal sorption was more selective on Al2O3 that showed a greater affinity towards Pb over Zn under competition, correlating with the reducible fraction of sequential extraction. Furthermore, significant amounts of Pb and Zn were additionally sorbed on SDBC following 30-day ageing. The X-ray diffraction revealed the formation of metal-phosphate precipitates, while the X-ray photoelectron spectroscopy showed a larger quantity of metal–oxygen bonding after 30-day ageing of metal-loaded SDBC. The results may imply favourable long-term transformation and additional sorption capacity of SDBC. In conclusion, SDBC resembles the sorption characteristics of both organic and mineral sorbents in different aspects, presenting an appropriate material for metal immobilization during soil amendment.
ano.nymous@ccsd.cnrs.fr.invalid (Weihua Zhang) 06 Feb 2017
https://hal.science/hal-01458427
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[hal-01260292] Toward the Standardization of Biochar Analysis: The COST Action TD1107 Interlaboratory Comparison
Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical−chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future.
ano.nymous@ccsd.cnrs.fr.invalid (Hans Jörg Bachmann) 21 Jan 2016
https://hal.science/hal-01260292
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[hal-01258345] Root development of non-accumulating and hyperaccumulating plants in metal-contaminated soils amended with biochar
Biochar may be used as an amendment in contaminated soils in phytoremediation processes. The mechanisms controlling plant metal uptake in biochar-amended soils remain however unclear. This work aimed at evaluating the influence of biochar on root development and its consequence on plant metal uptake, for two non-hyperaccumulating plants (Zea mays and Lolium perenne) and one hyperaccumulator of Cd and Zn (Noccaea caerulescens). We conducted rhizobox experiments using one acidic and one alkaline soil contaminated with Cd, Pb and Zn. Biochar was present either homogeneously in the whole soil profile or localized in specific zones. A phenomenon of root proliferation specific to biochar-amended zones was seen on the heterogeneous profiles of the acidic soil and interpreted by a decrease of soil phytotoxicity in these zones. Biochar amendments also favored root growth in the alkaline soil as a result of the lower availability of certain nutrients in the amended soil. This increase of root surface led to a higher accumulation of metals in roots of Z.mays in the acidic soil and in shoots of N. caerulescens in the alkaline soil. In conclusion, biochar can have antagonist effects on plant metal uptake by decreasing metal availability, on one hand, and by increasing root surface and inducing root proliferation, on the other hand.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 18 Jan 2016
https://hal.science/hal-01258345
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[hal-00926673] Short-term effects of biochar on soil heavy metal mobility are controlled by intra-particle diffusion and soil pH increase
Biochar, the solid product of biomass pyrolysis, can be used as a soil amendment to stabilize metals in contaminated soils. The effects of biochar on the mobility of metals in soils are, however, poorly understood. To identify the predominant processes, we focused on (i) a possible kinetic limitation by transport in biochar particles, (ii) the evolution of biochar mineral phases and (iii) the effect of biochar on soil pH. Batch experiments were conducted to measure the sorption kinetics of copper (Cu), cadmium (Cd) and nickel (Ni) and the sorption-desorption isotherms for lead (Pb), Cu, Cd, zinc (Zn) and Ni in a wood-derived biochar. Sorption data were then compared with extraction test results using biochar with one acidic and one basic soil contaminated by Zn, Cd and Pb. Kinetic results showed that biochar particle sizes controlled metal sorption rate despite a similar specific surface area, which indicated a limitation by intra-particle diffusion. Isotherms showed a partially reversible sorption to biochar following the order Pb>Cu>Cd≥Zn>Ni, which we explained primarily by the (co)precipitation of metals or their adsorption on specific biochar mineral phases. Effective metal immobilization was observed with biochar in both contaminated soils but could not be predicted from the sorption isotherms. This immobilization appeared to be governed by the soil pH increase, which induced a greater retention of metals on soil particles. Short-term effects of biochar on contaminated soils may therefore be controlled by diffusion in biochar particles and by soil alkalinization processes.
ano.nymous@ccsd.cnrs.fr.invalid (Frédéric Rees) 10 Jan 2014
https://hal.science/hal-00926673
