Comparing current chemical methods to assess biochar organic carbon in a Mediterranean agricultural soil amended with two different biochars

Raya-Moreno I., Cañizares R., Domene X., Carabassa V., Alcañiz J.M. (2017) Comparing current chemical methods to assess biochar organic carbon in a Mediterranean agricultural soil amended with two different biochars. Science of the Total Environment. 598: 604-618.
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Doi: 10.1016/j.scitotenv.2017.03.168

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Several methods have been proposed to quantify biochar C recalcitrance but their suitability is questionable. The aims of this work are: i) to compare the suitability of thermal or chemical oxidation and acid hydrolysis methods to quantify biochar C-pool in a biochar-amended soil, and ii) to calculate the biochar content in the soil through a mass balance derived from the obtained data. Two contrasted biochars from pine wood and corn cob remains were incorporated at a rate of 5 Mg C ha− 1 to a sandy loam vineyard soil with neutral pH and low organic carbon content, in field conditions. The analytical methods used to determine the oxidability and hydrolyzation of soil and biochar-C were: i) weight loss-on-ignition (LOI) at three temperatures (375 °C, 550 °C and 950 °C) for the assessment of organic matter, and ii) dry-combustion (TOC), strong (sO) and mild (mO) acid potassium dichromate oxidations, acid hydrolysis (AH) and peroxide oxidation (PO) for the assessment of organic C-pools. mO mainly estimated the easy oxidisable organic fraction of soil. Resistant organic carbon (ROC), estimated as non-hydrolysable organic carbon by AH and as non-oxidisable by mO, led to similar values in control soil (5 g C kg− 1 soil), whereas different ROC values were obtained in soils amended with biochar (6–12 g C kg− 1 soil). The suitability of these different methods as proxies to quantify biochar C was verified through a mass balance observing differences between them. PO removes well native soil organic matter, but also attacks partially biochar's fraction, so an underestimation exists. However, mO leaves intact biochar in the amended soil. Summarising, LOI, TOC and mO were the best proxies for biochar-C quantification, especially the last one, somewhat clarifying the debate on this topic. © 2017 Elsevier B.V.

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Gasifier biochar effects on nutrient availability, organic matter mineralization, and soil fauna activity in a multi-year Mediterranean trial

Marks E.A.N., Mattana S., Alcañiz J.M., Pérez-Herrero E., Domene X. (2016) Gasifier biochar effects on nutrient availability, organic matter mineralization, and soil fauna activity in a multi-year Mediterranean trial. Agriculture, Ecosystems and Environment. 215: 30-39.
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Doi: 10.1016/j.agee.2015.09.004

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Gasifier pine biochar is a carbon-rich material which may be useful as a soil amendment. In Europe and elsewhere there may be potential added value of char produced in industrial gasifiers, up to now considered as wastes. Pine gasification biochar was tested as a soil amendment in a multi-year Mediterranean barley crop field trial, applied at 12 and 50tha-1 while applying half the usual N rate at 50kgha-1, contrasted with a full 100kg ha-1 N fertilizer treatment without biochar. Over the 6-30 month period following the application, biochar treatments did not have any significant effect on soil microbial biomass, respiration, or metabolic coefficient. N mineralization as NO3 - was decreased by biochar at 6 and 12 months from experiment start and coincided with ammonium accumulation. Biochar increased overall soil concentrations of K+ and SO4 2-, attributed to a direct additive effect, agreeing with data from other sources. Biochar treatments (with half usual N fertilization) did not have any significant effects on barley crop parameters, and when biochar treatments were contrasted against full N fertilization with no biochar, the usual N dosage was clearly more beneficial to crop development. Finally, soil fauna activity was negatively impacted by gasifier biochar treatments in years two and three, indicating a risk to soil processes mediated by soil invertebrates. Though this gasifier biochar is expected to be highly stable and therefore of interest for carbon sequestration, its utilization therefore risks negative effects on some biologically-mediated soil processes at high application rates. © 2015 Elsevier B.V.

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Unintended effects of biochars on short-term plant growth in a calcareous soil

Marks E.A.N., Alcaniz J.M., Domene X. (2014) Unintended effects of biochars on short-term plant growth in a calcareous soil. Plant and Soil. : 0-0.
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Doi: 10.1007/s11104-014-2198-2

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Background and aims Biochar has demonstrably improved crop yields in weathered and acidic soils, but studies in calcareous soils are particularly lacking, so biochar effects on plant growth was investigated under these conditions. Methods Six biochars were obtained from different feedstocks and production technologies. Chemical characterization of fresh biochars included total and extractable nutrients, labile carbon, and Fourier transform infrared spectroscopy. Extractable nutrients were also evaluated in biochar-soil mixtures with a basic (pH >8.2) test soil. Bioassays with lettuce and ryegrass were carried out to relate biochar chemical properties to effects on plant biomass. Results A sewage sludge slow pyrolysis char was stimulatory to plant growth, as was a slow pyrolysis pine wood char at an intermediate concentration, while gasification and fast-pyrolysis pine and poplar wood chars were strongly inhibitory, with reductions in biomass at realistic application rates of 5-19 t ha-1. Conclusions Statistical comparison of plant responses with biochar composition led to the assessment that plant responses were most correlated with volatile matter content and total P content, whose availability was likely regulated by pH and Ca content. Potential effects of phytotoxins were considered, but these were seen to be much less probable than effects due to nutrient availability. © 2014 Springer International Publishing Switzerland.

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Biochars provoke diverse soil mesofauna reproductive responses inlaboratory bioassays

Marks E.A.N., Mattana S., Alcaniz J.M., Domene X. (2014) Biochars provoke diverse soil mesofauna reproductive responses inlaboratory bioassays. European Journal of Soil Biology. 60: 104-111.
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Doi: 10.1016/j.ejsobi.2013.12.002

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Biochar application to soil has the potential to improve soil fertility under certain conditions. However, potential ecological effects remain largely unexplored and poorly understood, particularly those on soil biota. Six biochars were tested on two soil-dwelling invertebrates in short-term bioassays to determine effects on survival and reproduction. A pine wood gasification char increased collembolan adult mortality at high concentrations. Wood slow and fast pyrolysis biochars had a strong stimulatory effect on collembolan reproduction, but no strong effect on enchytraeids. A sewage sludge char was slightly stimulatory for both organisms, and a pine gasification char was inhibitory in both cases. Inhibitory effects were associated with biochars with high carbonate and Ca content and pH. In light of the high stimulation of collembolan reproduction, potential explanations such as soil microbial community shifts or gut symbiont use of biochar are suggested. © 2013 Elsevier Masson SAS.

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Applying a GLM-based approach to model the influence of soil properties on the toxicity of phenmedipham to Folsomia candida

Domene X., Chelinho S., Campana P., Alcañiz J.M., Römbke J., Sousa J.P. (2012) Applying a GLM-based approach to model the influence of soil properties on the toxicity of phenmedipham to Folsomia candida. Journal of Soils and Sediments. 12: 888-899.
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Doi: 10.1007/s11368-012-0502-4

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Purpose: Soil properties are the main explanation to the different toxicities obtained in different soils due to their influence on chemical bioavailability and the test species performance itself. However, most prediction studies are centred on a few soil properties influencing bioavailability, while their direct effects on test species performance are usually neglected. In our study, we develop prediction models for the toxicity values obtained in a set of soils taking into account both the chemical concentration and their soil properties. Materials and methods: The effects on the avoidance behaviour and on reproduction of the herbicide phenmedipham to the collembolan Folsomia candida is assessed in 12 natural soils and the Organisation for Economic Co-operation and Development (OECD) artificial soil. The toxicity outcomes in different soils are compared and explanatory models are constructed by generalised linear models (GLMs) using phenmedipham concentrations and soil properties. Results and discussion: At identical phenmedipham concentrations, the effects on reproduction and the avoidance response observed in OECD soil were similar to those observed in natural soils, while effects on survival were clearly lower in this soil. The organic matter and silt content explained differences in the avoidance behaviour in different soils; for reproduction, there was a more complex pattern involving several soil properties. Conclusions: Our results highlight the need for approaches taking into account all the soil properties as a whole, as a necessary step to improve the prediction of the toxicity of particular chemicals to any particular soil. © 2012 Springer-Verlag.

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Influence of soil properties on the performance of Folsomia candida: Implications for its use in soil ecotoxicology testing

Domene X., Chelinho S., Campana P., Natal-da-Luz T., Alcañiz J.M., Andrés P., Römbke J., Sousa P. (2011) Influence of soil properties on the performance of Folsomia candida: Implications for its use in soil ecotoxicology testing. Environmental Toxicology and Chemistry. 30: 1497-1505.
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Doi: 10.1002/etc.533

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Nineteen Mediterranean natural soils with a wide range of properties and the Organisation for Economic Co-operation and Development (OECD) artificial soil were used to assess the influence of soil properties on the results of avoidance and reproduction tests carried out with the soil collembolan species Folsomia candida. Compared to natural soils, the OECD soil was mostly rejected by individuals when a natural soil was offered in avoidance tests, and the number of offspring produced was generally lower than the one obtained in natural soils. None of the soil properties assessed showed a significant influence on the avoidance behavior. More precisely, only soil moisture was included in the model explaining the avoidance response (avoidance increased with increasing differences in moisture), but its contribution was marginally not significant. The model derived explained only 16% of the variance in avoidance response. On the contrary, several soil properties significantly influenced reproduction (number of offspring increased with increasing moisture content, increasing coarse texture, and decreasing nitrogen content). In this case, the model explained 45% of the variance in reproduction. These results, together with the fact that most of the selected soils fulfilled the validity criteria in both avoidance and reproduction tests, confirm the literature experience showing that this species is relatively insensitive to soil properties and hence highly suitable to be used in ecotoxicological tests with natural soils. In addition, our study highlights the need for accuracy in soil moisture adjustment in soil ecotoxicological tests with this species. Otherwise, results of both avoidance and reproduction tests might be biased. © 2011 SETAC.

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Soil bioassays as tools for sludge compost quality assessment

Domene X., Solà L., Ramírez W., Alcañiz J.M., Andrés P. (2011) Soil bioassays as tools for sludge compost quality assessment. Waste Management. 31: 512-522.
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Doi: 10.1016/j.wasman.2010.10.013

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Composting is a waste management technology that is becoming more widespread as a response to the increasing production of sewage sludge and the pressure for its reuse in soil. In this study, different bioassays (plant germination, earthworm survival, biomass and reproduction, and collembolan survival and reproduction) were assessed for their usefulness in the compost quality assessment. Compost samples, from two different composting plants, were taken along the composting process, which were characterized and submitted to bioassays (plant germination and collembolan and earthworm performance). Results from our study indicate that the noxious effects of some of the compost samples observed in bioassays are related to the low organic matter stability of composts and the enhanced release of decomposition endproducts, with the exception of earthworms, which are favored. Plant germination and collembolan reproduction inhibition was generally associated with uncomposted sludge, while earthworm total biomass and reproduction were enhanced by these materials. On the other hand, earthworm and collembolan survival were unaffected by the degree of composting of the wastes. However, this pattern was clear in one of the composting procedures assessed, but less in the other, where the release of decomposition endproducts was lower due to its higher stability, indicating the sensitivity and usefulness of bioassays for the quality assessment of composts. © 2010 Elsevier Ltd.

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Role of soil properties in sewage sludge toxicity to soil collembolans

Domene X., Colón J., Uras M.V., Izquierdo R., Àvila A., Alcañiz J.M. (2010) Role of soil properties in sewage sludge toxicity to soil collembolans. Soil Biology and Biochemistry. 42: 1982-1990.
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Doi: 10.1016/j.soilbio.2010.07.019

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Soil properties are one of the most important factors explaining the different toxicity results found in different soils. Although there is knowledge about the role of soil properties on the toxicity of individual chemicals, not much is known about its relevance for sewage sludge amendments. In particular little is known about the effect of soil properties on the toxicity modulation of these complex wastes. In addition, in most studies on sewage sludges the identity of the main substances linked to the toxicity and the influence of soil properties on their bioavailability remains unknown.In this study, the toxicity of a sewage sludge to the soil collembolan Folsomia candida was assessed in nine natural soils from agricultural, grassland and woodland sites, together with the OECD soil. Correlations between the relative toxicity of sludge for collembolans in the different soils and their physical and chemical soil properties were assessed in order to identify the main compounds responsible for the effects observed. Furthermore, the relationships between the toxic effects to collembolans and water-soluble ions released by sludge, pH and electric conductivity were also assessed, together with the modulating effects of soil properties.Sludge toxicity was directly linked to the water extractable ammonium, which explained most of the mortality of the collembolans, and part of the inhibition of reproduction. For the last endpoint, nitrite also contributed significantly to the inhibition observed. The varied levels in water extractable ammonium in the different soils at equal dosages seem to be, in turn, modulated by some soil properties. Higher organic carbon contents were associated with lower toxicity of sludge, both for survival and reproduction, probably related to its higher ammonium sorption capacity. In addition, for reproduction, increasing the C/N ratio and pH appeared to increase the toxicity, probably due to both the greater difficultly in nitrification and the known unsuitability of alkaline soils for this species. © 2010 Elsevier Ltd.

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Bioassays prove the suitability of mining debris mixed with sewage sludge for land reclamation purposes.

Domene X, Mattana S, Ramírez W, Colón J, Jiménez P, Balanyà T, Alcañiz JM, Bonmatí M (2010) Bioassays prove the suitability of mining debris mixed with sewage sludge for land reclamation purposes. Journal of Soils Sediments 10: 30-44. doi 10.1007/s11368-009-0073-1.

Bioassays prove the suitability of mining debris mixed with sewage sludge for land reclamation purposes

Domene X., Mattana S., Ramírez W., Colón J., Jiménez P., Balanyà T., Alcañiz J.M., Bonmatí M. (2009) Bioassays prove the suitability of mining debris mixed with sewage sludge for land reclamation purposes. Journal of Soils and Sediments. 10: 30-44.
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Doi: 10.1007/s11368-009-0073-1

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Background, aim, and scope: Mining activities disturb land and reduce its capacity to support a complete functional ecosystem. Reclamation activities in this case are not easy due to the large amount of soil required. This is why mining debris are usually used as surrogate of soil, despite their unsuitable physicochemical properties. However, these properties can be improved with the amendment using an organic source, usually sewage sludge. Nevertheless, the use of sludge might lead to impacts on soil and water ecosystems because of its physicochemical properties and pollutant content. The aim of this study is to assess the suitability of the use of mining debris amended with sewage sludge as practice for the reclamation of land degraded by limestone-quarrying activities. Materials and methods: Two different types of mining debris from the same limestone quarry and six different types of composted or thermally dried sewage sludge were studied. A laboratory assessment was carried out by means of standardized bioassays of sludges, together with a field assessment carried out in lysimeters filled with debris-sludge mixtures. The field assessment was carried out using both the soil-waste mixtures, amended with dosages similar to those used for restoration purposes and their corresponding leachates. The variation of physicochemical properties and the outcomes of different bioassays (soil microorganisms biomass and respiration, enzymatic activities, plant emergence and growth, collembolan survival and reproduction, and the Microtox assay) were used as indicators of fertilizing or ecotoxicological effects. Results: The mining debris used in our study showed a poor capacity for biological recovery, as shown by the lower biological outcomes measured in control lysimeters compared to lysimeters amended with sludge. The addition of sludge improved debris just before the sludge application in terms of its physicochemical and biological properties (microorganism's biomass, respiration and enzymatic activities) which, in some cases, persisted after a year. Conversely, in some sludges, an inhibition in soil collembolans was observed just before the amendment, but any inhibitory effect disappeared after a year. Concerning the leachates obtained from field lysimeters after a week and a year, no inhibitory effects were detectable for aquatic bacteria. Discussion: The effects observed on some of the measured biological endpoints, both in laboratory and field assays, were mainly mediated by physicochemical parameters related to a low stability of organic matter, but in the opposite sense depending on the organism considered. Microbial parameters were enhanced when the organic matter added had a low stability (high content in labile organic matter) but, on the other hand, collembolan performance was negatively affected. The lack of toxicity of leachates indicates a low risk for groundwaters of this reclamation practice. Conclusions: The results of this study support the use of mining debris mixed with sludge for land reclamation of degraded land by quarrying. The addition of sludge allowed a quick plant cover re-establishment and provided a suitable habitat for soil biota because no long-term ecotoxicological risks were observed neither for soils nor groundwaters. The results also indicate that the environmental risk of sludges might be reduced using sludges with a high content in stable organic matter. Recommendations and perspectives: The use of mining debris mixed with sewage sludges for mining reclamation purposes is suitable since long-term ecotoxicological risks were not observed. In addition, the results support the suitability of bioassays for the prediction of the success or risk of specific land reclamation practices in order to avoid unsuccessful attempts. © Springer-Verlag 2009.

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