Analysis of total organic carbon in soil-biochar systems

Amending agricultural soils with biochar can contribute to negative carbon strategies when the resistance to oxidation of soil carbon is improved (avoided CO2 emission) and plant growth is promoted (increased CO2 fixation). The environmental stability and sequestering capacity of biochar is dependent on the chemical form of carbon and its physical location in the carbonaceous matrix. The addition of biochar in soil increases noticeably the stable carbon pool, while the effect on labile carbon, including polyaromatic structures, is less marked.1 The fertilizing action can be lost if biochar is removed from the cultivated area due to physical processes (vertical transport, lateral export, slacking). Assessing the fate of carbon in the soil requires the use of suitable analytical methods that should be validated for the presence of biochar. Please click on the file below for full content of the abstract

Biochar from gasification in cultivated soils and riparian buffer zones: Chemical characterization

During rain events, pollutants in agricultural soils can be transported from fields to surface and/or groundwater resulting in contamination of streams and rivers. Researchers and farmers must work together to find solutions to ensure the preservation of crop production without jeopardizing water quality or the health of the ecosystem. Establishment of riparian zones may reduce the effects of diffuse discharges of pollutants into waterways. The addition of biochar to soils, particularly in a riparian zones, can reduce the mobility of contaminants and improve removal efficiency due its sorptive capacity. Please click on the file below for full content of the abstract

Fate of soil organic carbon and polycyclic aromatic hydrocarbons in a vineyard soil treated with biochar

The effect of biochar addition on the levels of black carbon (BC) and polcyclic aromatic hydrocarbons (PAHs) in a vineyard soil in central Italy was investigated within a two year period. Hydropyrolysis (HyPy) was used to determine the contents of BC (BCHyPy) in the amended and control soils while the hydrocarbon composition of the semi-labile (non-BCHyPy) fraction released by HyPy was determined by gas chromatography-mass spectrometry, together with the solvent-extractable PAHs. The concentrations of these three polycyclic aromatic carbon reservoirs, changed and impacted differently on the soil organic carbon over the period of the trial. The addition of biochar (33 ton dry biochar ha-1) gave rise to a sharp increase in soil organic carbon which could be accounted for by an increase of BCHyPy. Over time, the concentration of BCHyPy decreased significantly from 36 to 23 mg g-1, and as a carbon percentage from 79% to 61%. No clear time trends were observed for the non-BCHyPy PAHs varying from 39 to 34 µg g-1 in treated soils, not significantly different from control soils. However, the concentrations of extractable PAHs increased markedly in the amended soils, and decreased with time from 153 to 78 ng g-1 remaining always higher than those in untreated soil. The extent of the BCHyPy loss was more compatible with physical rather than chemical processes

Molecular characterization of the thermally labile fraction of biochar by hydropyrolysis and pyrolysis-GC/MS

Agroenvironmental benefits and limitations of biochar in soil applications require a full understanding of the stability and fate of the various carbon fractions. Analytical hydropyrolysis (HyPy) enables the determination of the stable black carbon (BCHyPy) and thermally labile (semi-labile; non-BCHyPy) fractions in biochar and soil samples. The non-BCHyPy fraction can be analysed at a molecular level by gas chromatography-mass spectrometry (GC-MS). In the present study, HyPy was applied to the characterisation of biochars produced from pine wood, beech wood and corn digestate with the same pyrolysis unit at low (340–400 °C) and high (600 °C) temperatures. Results were compared with those from Py-GC-MS. HyPy provided consistent information concerning the thermal stability of biochar samples, with BCHyPy levels related with the relative abundance of the charred fraction estimated by Py-GC-MS and the hydrogen/carbon (H/C) ratios. The non-BCHyPy fractions were featured by the presence of polycyclic aromatic hydrocarbons (PAHs) from two to seven rings, including alkylated derivatives up to C4. Partially hydrogenated PAHs were also detected. The yields of non-BCHyPy were higher for those biochars produced at lower temperatures and always more abundant than the levels of solvent-extractable PAHs. The methylated/parent PAH ratios from HyPy and Py-GC-MS exhibited lower values for the most charred biochar. The observed differences in the abundance of the stable fraction and the molecular chemistry of the semi-labile fraction can be usefully utilised to drive the process conditions to the desired properties of the resulting biochars and to predict the impact of biochar amendment to soil organic pools. The concentrations of priority PAHs in the semi-labile fraction was evaluated in the mg g−1 level suggesting that it could be an important fraction of the polyaromatic carbon pool in soil

Determination of polycyclic aromatic hydrocarbons (PAHs) in an agricultural soil treated with biochar

The unavoidable presence of hazardous PAHs in biochar is a matter of concern due to possible health and ecological risks associated to its application in soils. Besides the direct effect of increased environmental PAH concentrations resulting from its use, a variety of indirect and ancillary factors may affect the behavior of biochar amended soils as a sink or source of PAHs. Understanding the impact of biochar on soil quality needs a considerable effort from laboratory and field studies. This contribution reports on the levels of PAHs in a cultivated soil one year after the addition of biochar. Biochar, deriving from slow pyrolysis of pruning orchard, was superficially distributed in the inter-row space of a vineyard at a rate of 22 t ha-1 in 2009 following a randomized block layout with 5 replicates and incorporated into the soil with a chisel plow tiller in the 0-30 cm depth. Soil is a sandy clay loam with sub-acid pH (5.4). Two soil sampling campaigns were made in August and December 2010. An analytical procedure targeted to the determination of PAHs in both biochar and soil matrices was recently developed [1]. Briefly, samples were spiked with surrogate PAHs, then PAHs were soxhlet extracted for 36 hours with an acetone/cyclohexane 1:1 mixture, purified by silica gel solid phase extraction (SPE) and analysed by GC-MS(SIM). The method was validated with the certified reference soil CRM (ERM-CC013a). All the US EPA PAHs were detected in the utilised biochar and summed up to 3.5 µg g-1, with naphthalene as the most abundant species followed by phenanthrene. The untreated soil samples exhibited total PAH concentrations two orders of magnitude lower than that of biochar and with a different distribution pattern characterised by higher abundance of phenanthrene and fluorene. After almost one year following biochar application, the total mean concentration values of PAHs in amended soils resulted higher than those of the untreated soils, both in August (52 vs. 31 ng g-1) and December (35 vs. 27 ng g-1). However, the differences were not statistically significant due to the high dispersion of PAH values between samples withdrawn from the same parcel (n = 5). The lower concentrations observed in winter for the treated soils suggest a seasonal variability superimposed to sampling heterogeneity. These preliminary results suggest that the soil contamination by PAHs following biochar application is not significant at the application rates currently recommended in agriculture (20–60 t ha-1) and the PAH load typically found in biochar from slow pyrolysis [1]. The long term persistence of PAHs and their potential to be bioaccumulated is under investigation. [1] D. Fabbri, A.G. Rombolà, C. Torri, K. A. Spokas, J.Anal.Applied Pyrol., 2012), http://dx.doi.org/10.1016/j.jaap.2012.10.003

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.ISSN:0021-8561ISSN:1520-511