Ronald J. Smernik

Comparison of quantification methods to measure fire‐derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere

Black carbon (BC), the product of incomplete combustion of fossil fuels and biomass (called elemental carbon (EC) in atmospheric sciences), was quantified in 12 different materials by 17 laboratories from different disciplines, using seven different methods. The materials were divided into three classes: (1) potentially interfering materials, (2) laboratory-produced BC-rich materials, and (3) BC-containing environmental matrices (from soil, water, sediment, and atmosphere). This is the first comprehensive intercomparison of this type (multimethod, multilab, and multisample), focusing mainly on methods used for soil and sediment BC studies. Results for the potentially interfering materials (which by definition contained no fire-derived organic carbon) highlighted situations where individual methods may overestimate BC concentrations. Results for the BC-rich materials (one soot and two chars) showed that some of the methods identified most of the carbon in all three materials as BC, whereas other methods identified only soot carbon as BC. The different methods also gave widely different BC contents for the environmental matrices. However, these variations could be understood in the light of the findings for the other two groups of materials, i.e., that some methods incorrectly identify non-BC carbon as BC, and that the detection efficiency of each technique varies across the BC continuum. We found that atmospheric BC quantification methods are not ideal for soil and sediment studies as in their methodology these incorporate the definition of BC as light-absorbing material irrespective of its origin, leading to biases when applied to terrestrial and sedimentary materials. This study shows that any attempt to merge data generated via different methods must consider the different, operationally defined analytical windows of the BC continuum detected by each technique, as well as the limitations and potential biases of each technique. A major goal of this ring trial was to provide a basis on which to choose between the different BC quantification methods in soil and sediment studies. In this paper we summarize the advantages and disadvantages of each method. In future studies, we strongly recommend the evaluation of all methods analyzing for BC in soils and sediments against the set of BC reference materials analyzed here.

An investigation into the reactions of biochar in soil

Interactions between biochar, soil, microbes, and plant roots may occur within a short period of time after application to the soil. The extent, rates, and implications of these interactions, however, are far from understood. This review describes the properties of biochars and suggests possible reactions that may occur after the addition of biochars to soil. These include dissolution-precipitation, adsorption-desorption, acid-base, and redox reactions. Attention is given to reactions occurring within pores, and to interactions with roots, microorganisms, and soil fauna. Examination of biochars (from chicken litter, greenwaste, and paper mill sludges) weathered for 1 and 2 years in an Australian Ferrosol provides evidence for some of the mechanisms described in this review and offers an insight to reactions at a molecular scale. These interactions are biochar- and site-specific. Therefore, suitable experimental trials—combining biochar types and different pedoclimatic conditions—are needed to determine the extent to which these reactions influence the potential of biochar as a soil amendment and tool for carbon sequestration.

Biochar carbon stability in a clayey soil as a function of feedstock and pyrolysis temperature.

The stability of biochar carbon (C) is the major determinant of its value for long-term C sequestration in soil. A long-term (5 year) laboratory experiment was conducted under controlled conditions using 11 biochars made from five C3 biomass feedstocks (Eucalyptus saligna wood and leaves, papermill sludge, poultry litter, cow manure) at 400 and/or 550 °C. The biochars were incubated in a vertisol containing organic C from a predominantly C4-vegetation source, and total CO(2)-C and associated δ(13)C were periodically measured. Between 0.5% and 8.9% of the biochar C was mineralized over 5 years. The C in manure-based biochars mineralized faster than that in plant-based biochars, and C in 400 °C biochars mineralized faster than that in corresponding 550 °C biochars. The estimated mean residence time (MRT) of C in biochars varied between 90 and 1600 years. These are conservative estimates because they represent MRT of relatively labile and intermediate-stability biochar C components. Furthermore, biochar C MRT is likely to be higher under field conditions of lower moisture, lower temperatures or nutrient availability constraints. Strong relationships of biochar C stability with the initial proportion of nonaromatic C and degree of aromatic C condensation in biochar support the use of these properties to predict biochar C stability in soil.

Estimation of charcoal (char) in soils.

Abstract A method for the semiquantitative estimation of charcoal (char) in soils is reported. The technique, performed on the 90% of soil char in the <53 μm fraction. Because of the assumptions used, estimates of char by this approach must be considered to be semiquantitative, but are conservative and provide estimates of the minimum char content of a soil.

The use of spin counting for determining quantitation in solid state 13C NMR spectra of natural organic matter: 1. Model systems and the effects of paramagnetic impurities

The degree of quantitation achieved in the solid state 13C nuclear magnetic resonance (NMR) spectra of a number of organic materials, an HF-treated soil, and a whole soil, was determined for both cross-polarisation (CP) and Bloch decay (BD) techniques using spin-counting experiments. The percentage of potential 13C NMR signal, which was actually observed (Cobs) was in the range 79–107% for the BD technique and in the range 29–103% for the CP technique. A number of materials, including cellulose, pectin, lignin, and palmitic acid gave quantitative spectra using both CP and BD. A second group, including chitin, collagen, and the HF-treated soil gave quantitative BD spectra, but significantly diminished CP spectra (Cobs-CP=66–75%). A third group including charcoal, a commercial humic acid, and the whole soil gave significantly diminished BD spectra (Cobs-BD=79–87%) and severely diminished CP spectra (Cobs-CP=29–35%). Signal losses in the CP spectra were attributed to rapid relaxation rates (short T1ρH) and/or slow magnetisation build-up rates (long TCH). The spin dynamics of the CP experiment were studied and a new method for correcting for differences in T1ρH between the sample and the reference in CP spin-counting experiments was developed. Signal produced by the Kel-F rotor end-caps was significant for the BD spectra and a correction for the end-cap spectrum was required prior to spin counting. The low 1H content of the fluorinated Kel-F polymer ensured that the contribution of end-caps to the CP spectra was insignificant. The effects of paramagnetic cations on quantitation in solid state NMR spectra was investigated by doping model compounds with paramagnetic impurities. Three mechanisms, which bring about signal loss and operate on three different length scales, were identified. The magnitude of the signal loss brought about by a paramagnetic material was shown to be dependent on both the type of cation involved and on the intimacy of contact with the organic matrix. Chemically bound paramagnetic cations were shown to result in large signal losses in the CP spectrum, whereas paramagnetic salts in a physical mixture with an organic material affected both CP and BD spectra equally.

Chemical and structural properties of carbonaceous products obtained by pyrolysis and hydrothermal carbonisation of corn stover

The main properties of chars produced from corn stover, either by pyrolysis at 550°C (to produce biochar) or by hydrothermal carbonisation (to produce hydrochar), were studied. Carbonaceous materials were characterised by: SEM imaging, solid-state 13C NMR, FT-IR, Raman spectroscopy, and XPS. The following parameters were determined: elemental composition, cation exchange capacity, acid groups contents, BET, and yield. The hydrochar had a low ash content and low pH (4.7); recovery of C was high (57%), although only about half of the C was aromatic. Atomic O/C and H/C ratios in the hydrochar were higher than in the biochar. The same pattern was observed for the estimated concentration of carboxylic functional groups (0.07 compared with 0.04 mol/kg). The biochar had higher ash content than the hydrochar, and also higher pH (~10) (lime equivalence ~40 kg CaCO3/t). The C recovery (46%) was lower than in the hydrochar, although most of the C recovered was aromatic. Both chars could be used as soil amendments, for very different requirements. Soil responses and the residence times of the chars (especially the hydrochar) must be studied in detail to pursue long-term C sequestration.

Characteristics of biochar: organo-chemical properties

Preface Foreword by Tim Flannery 1. Biochar for Environmental Management: An Introduction 2. Physical Properties of Biochar 3. Characteristics of Biochar: Microchemical Properties 4. Characteristics of Biochar: Organo-chemical Properties 5. Biochar: Nutrient Properties and Their Enhancement 6. Characteristics of Biochar: Biological Properties 7. Developing a Biochar Classification and Test Methods 8. Biochar Production Technology 9. Biochar Systems 10. Changes of Biochar in Soil 11. Stability of Biochar in Soil 12. Biochar Application to Soil 13. Biochar and Emissions of Non-CO2 Greenhouse Gases from Soil 14. Biochar Effects on Soil Nutrient Transformations 15. Biochar Effects on Nutrient Leaching 16. Biochar and Sorption of Organic Compounds 17. Test Procedures for Determining the Quantity of Biochar within Soils 18. Biochar, Greenhouse Gas Accounting and Emissions Trading 19. Economics of Biochar Production, Utilization and Greenhouse Gas Offsets 20. Socio-economic Assessment and Implementation of Small-scale Biochar Projects 21. Taking Biochar to Market: Some Essential Concepts for Commercial Success 22. Policy to Address the Threat of Dangerous Climate Change: A Leading Role for Biochar Index

The use of spin counting for determining quantitation in solid state 13C NMR spectra of natural organic matter: 2. HF-treated soil fractions

Spin counting experiments were used to determine the degree of quantitation achieved in solid state 13C NMR spectra of HF-treated, <53 μm fractions of eight soils. Observabilities were determined for both cross-polarisation (Cobs-CP) and Bloch decay (Cobs-BD) techniques. Cobs-BD ranged between 84% and 106%, indicating that practically all potential signal was observed. Therefore, the BD spectra quantitatively reflected the distribution of 13C environments present in the soils. Cobs-CP ranged between 54% and 83%, indicating that, although the majority of potential signal was observed, there was a significant fraction of potential NMR signal in each soil that was not detected using the CP technique. Comparison of the BD and CP spectra indicated that the decrease in signal intensity in the CP spectra was more evident for some resonances than for others. The O-alkyl region of the CP NMR spectrum was the least affected and the aromatic region was the most affected for the majority of the soils. This was due, in large part, to the presence of char in the most affected soils, in keeping with the low value of Cobs-CP reported for charcoal. The carbonyl and alkyl resonances were also under-represented in the CP spectra of some of the soils.

The chemical nature of P accumulation in agricultural soils-implications for fertiliser management and design: An Australian perspective

Many agricultural soils worldwide in their natural state are deficient in phosphorus (P), and the production of healthy agricultural crops has required the regular addition of P fertilisers. In cropping systems, P accumulates almost predominantly in inorganic forms in soil, associated with aluminium, calcium and iron. In pasture soils, P accumulates in both inorganic and organic forms, but the chemical nature of much organic P is still unresolved. The P use efficiency (PUE) of fertilisers is generally low in the year of application, but residual effectiveness is important, highlighting the importance of soil P testing prior to fertiliser use. With increasing costs of P fertiliser, various technologies have been suggested to improve PUE, but few have provided solid field evidence for efficacy. Fluid fertilisers have been demonstrated under field conditions to increase PUE on highly calcareous soils. Slow release P products have been demonstrated to improve PUE in soils where leaching is important. Modification of soil chemistry around the fertiliser granule or fluid injection point also offers promise for increasing PUE, but is less well validated. Better placement of P, even into subsoils, also offers promise to increase PUE in both cropping and pasture systems.

The influence of sewage sludge properties on sludge-borne metal availability

With the advent of more stringent controls on wastewater treatment, sewage sludge production in Europe and many parts of the world is increasing. With this increase comes the problem of sludge disposal, and recycling to land arguably offers an economically and environmentally sustainable option. However, a major limitation of sewage sludge reuse is the potential release of heavy metals from the sludge and heavy metal accumulation to toxic levels in topsoils. The properties of the sludge play a crucial role in determining the initial release and subsequent availability of heavy metals in amended soils. Bioavailable forms of heavy metals in recently amended soils are most likely to be those that are bioavailable in the sewage sludge. In this paper, published research on the importance of sewage sludge characteristics on metal release and bioavailability will be reviewed and contrasted with original research. A selection of sludges from around Australia has been collected for this purpose. Through the use of incubation studies, isotope dilution techniques, ion-selective electrode measurements and 13C-NMR spectroscopy, the importance of a range of sludge properties on heavy metal behaviour in sludges and sludge-amended soils is addressed.