This study describes a multivariate statistical model (derived using partial least squares regression, PLS-R) that derives charring intensity (reaction temperature and duration) from the attenuated total reflectance (ATR) Fourier Transform Infrared (FTIR) spectra of charcoal. Data for the model was obtained from a library of charcoal samples produced under laboratory conditions at charring intensities (CI) relevant to wildfires and a series of feedstocks representing common tree species collected from Australia. The PLS-R model developed reveals the potential of FTIR to determine the charring intensity of charcoal. Though limited by the differences between laboratory-produced charcoal and the more heterogeneous and less-structured charcoal produced in a wildfire, the method was tested against fossil charcoal from a well-dated sediment core collected from Thirlmere Lakes National Park, Australia and showed a distinct change in CI that can be related to other climatic and environmental proxies. We suggest that the method has the potential to offer insights into the conditions under which natural charcoal is formed including the modelling of charring intensities of fossil charcoal samples isolated from sediments, archaeological applications or characterisation of contemporary fire events from charcoal in soils.

Biochar-based compound fertilizers (BCF) and amendments have proven to enhance crop yields and modify soil properties (pH, nutrients, organic matter, structure etc.) and are now in commercial production in China. While there is a good understanding of the changes in soil properties following biochar addition, the interactions within the rhizosphere remain largely unstudied, with benefits to yield observed beyond the changes in soil properties alone. We investigated the rhizosphere interactions following the addition of an activated wheat straw BCF at an application rates of 025% (g.g(-1) soil), which could potentially explain the increase of plant biomass (by 67%), herbage N (by 40%) and P (by 46%) uptake in the rice plants grown in the BCF-treated soil, compared to the rice plants grown in the soil with conventional fertilizer alone. Examination of the roots revealed that micron and submicron-sized biochar were embedded in the plaque layer. BCE increased soil Eh by 85 mV and increased the potential difference between the rhizosphere soil and the root membrane by 65 my. This increased potential difference lowered the free energy required for root nutrient accumulation, potentially explaining greater plant nutrient content and biomass. We also demonstrate an increased abundance of plant-growth promoting bacteria and fungi in the rhizosphere. We suggest that the redox properties of the biochar cause major changes in electron status of rhizosphere soils that drive the observed agronomic benefits. (C) 2020 The Authors. Published by Elsevier B.V.

Soils are known to differ in suppressiveness to soil-borne diseases, but the suppressiveness or otherwise to Fusarium wilt of Australian soils used to grow bananas is unknown. In this work we tested the relative suppressiveness of six key soil types. Banana (Musa (AAB group) ‘Pome’, cultivar ‘Lady Finger’) was grown in pots of the soils inoculated or not with Fusarium oxysporum f.sp. cubense (Foc) ‘Race 1’. Sixteen weeks after inoculation the plants were harvested and disease severity was assessed by measuring discoloration within the rhizome. In the inoculated pots, disease severity was greatest in the alluvial Liverpool and Virgil soils and least in the basaltic origin Tolga soil. No disease was detected in the non-inoculated pots. Soils with the lowest disease severity had the highest root mass, irrespective of inoculation, and the largest (negative) effect of inoculation on root dry mass. Disease severity in inoculated pots was negatively correlated with soil clay content and β-glucosidase activity. The results indicate that the risk of Fusarium wilt negatively impacting banana growth differs between soils of the main Australian banana-growing region.

19 Pyrolised carbon in biochar can sequester atmospheric CO2 into soil to reduce impacts of 20 anthropogenic CO2 emissions. When estimating the stability of biochar, degradation of biochar 21 carbon, mobility of degradation products and ingress of carbon from other sources must all be 22 considered. In a previous study we tracked degradation in biochars produced from radiocarbon-free 23 wood and subjected to different physico-chemical treatments over three years in a rainforest soil. 24 Following completion of the field trial, we report here a series of in-vitro incubations of the 25 degraded biochars to determine CO2 efflux rates, C concentration and δC values in CO2 to 26 quantify the contributions of biochar carbon and other sources of carbon to the CO2 efflux. The C 27 concentration in CO2 showed that microbial degradation led to respiration of CO2 sourced from 28 biochar carbon (≈ 0.5 1.4 μmoles CO2 / g biochar C / day) along with a component of carbon closely 29 associated with the biochars but derived from the local environment. Correlations between C 30

ABSTRACTPyrolized carbon in biochar can sequester atmospheric CO2 into soil to reduce impacts of anthropogenic CO2 emissions. When estimating the stability of biochar, degradation of biochar carbon, mobility of degradation products, and ingress of carbon from other sources must all be considered. In a previous study we tracked degradation in biochars produced from radiocarbon-free wood and subjected to different physico-chemical treatments over three years in a rainforest soil. Following completion of the field trial, we report here a series of in-vitro incubations of the degraded biochars to determine CO2 efflux rates, 14C concentration and δ13C values in CO2 to quantify the contributions of biochar carbon and other sources of carbon to the CO2 efflux. The 14C concentration in CO2 showed that microbial degradation led to respiration of CO2 sourced from indigenous biochar carbon (≈0.5–1.4 μmoles CO2/g biochar C/day) along with a component of carbon closely associated with the biochars but derived from the local environment. Correlations between 14C concentration, δ13C values and Ca abundance indicated that Ca2+ availability was an important determinant of the loss of biochar carbon.

The activities of the soil microbiota are essential to the long-term sustainability of agricultural systems, through their influences on biological, chemical and physical processes, which drive essential ecosystem services. Moreover, changes in microbial communities are considered as precursors to changes in the health and viability of the soil environment, due to their responses to changes in agricultural management practices. Therefore, measurements of soil microbial activity and diversity are ideal indicators for monitoring soil status and the efficacy of soil management. However, due to the vast taxonomic diversity of soil microorganisms, analysis of microbial diversity is often problematic, time consuming and costly. Two banana experiments were established in far north Queensland, Australia, under different nutrient and groundcover management practices, to understand the dynamic changes in soil microbial communities and their effectiveness to sustain ecosystem services, such as organic matter decomposition and disease suppression. Using a functional approach, soil biological communities were analysed using trophic analysis of soil nematode communities, community level physiological profiles and enzyme activity assays. A reduction in nitrogen fertiliser inputs was related to a greater number of fungivorous nematodes which was also linked to greater suppression of Fusarium oxysporum f. sp. cubense using a novel soil-baiting bioassay. Furthermore, community-level physiological profiles enabled differentiation of soils over time demonstrating a shift in soil microbial functional diversity. The results highlight how soil management can drive differences in soil microbial activity and diversity to improve soil functions in banana production.

Quantification of soil organic carbon (SOC) content is important for sustainable agricultural management and accurate carbon accounting. Infrared (IR) absorbance can be used to estimate SOC content, but the relationship differs between regions due to matrix effects. We developed an IR-based model specific for SOC in Papua New Guinean soils. A total of 437 samples from 0.0–0.3m depth were analysed for SOC using Dumas combustion. IR absorption spectra were collected from the same samples, and a predictive regression model was developed using the 6000–1030cm–1 spectral range. Using a validation set, predicted SOC values resulting from the IR-based model compared well with values from Dumas combustion (R2=0.905; ratio of performance-to-deviation=5.64). Constraining wavelengths to positively correlated regions of the spectra was also explored and showed improved model performance (R2=0.932). Overall, IR analysis provides a robust method for estimating SOC content for a range of Papua New Guinean soils.

Biochar thermosequences produced from the charring of poultry manure and freshwater macroalgae feedstocks between 300 and 700 degrees C were analyzed by pyrolysis-GC-MS to assess the nature of the thermochemical conversion of N-rich feedstocks. With increasing charring temperature (T-CHAR), the products of intact lignin, protein and polysaccharides decreased whereas those of charred aromatic domains (monocyclic and polycyclic aromatic hydrocarbons, benzonitriles) increased. These results are in agreement with thermosequences obtained from lignocellulosic feedstocks under the same analytical conditions. Therefore, we aimed to create a universal proxy of the degree of thermochemical alteration of biochar thermosequences from diverse series of feedstocks (gorse wood, chestnut wood, rice straw, poultry manure, freshwater algae and tannin) using Principal Components Analysis (PCA). From the PCA the relation of pyrolysis products with charring intensity was established and translated to Thermal Stability Indices (TSIp), which then gave rise to calculations of TSI of the biochars (TSIb). The TSIp varied only slightly between the different feedstocks suggesting that they could be used in future research to interpret pyrolysis fingerprints for a wide range of different biochars. In addition, TSIb can be used as a thermostability proxy for biochars and were found to be more reliable than other pyrolytic proxies such as the benzene/toluene or naphthalene/C-1-naphthalenes ratios. This study marks the first attempt to develop a single proxy of stability for biochars at T-CHAR from pyrolysis fingerprints using 157 common pyrolysis products. These proxies will provide a simple measure for the usefulness of a biochar for C sequestration and/or soil amelioration. (C) 2017 Elsevier Ltd. All rights reserved.

[Extract] Hydropyrolysis (hydrogen pyrolysis or HyPy) was developed in the 1950s as a process for the direct conversion of coal into methane and light aromatic feedstocks using extremely high temperatures and pressures, ~800°C and up to 300 bar (Hiteshue et al. 1957). During the late 1980s, it was found that by using dispersed catalysts, such as sulfided molybdenum (Mo), it was possible to achieve much higher overall conversions to liquid products at pressures no higher than 150 bar (Snape et al. 1989). These developments laid the foundation for the development of HyPy as an analytical pyrolysis procedure based on the unique ability of HyPy to produce high yields of biomarkers from petroleum source rocks, achieving overall conversions close to 100% for macromolecular labile organic matter, while, at the same time, minimising structural alteration of the products by isomerisation and cracking (Love et al. 1995). This has enabled the technique to be used in petroleum geochemistry for applications where conventional geochemical approaches fail; for example, the characterisation of heavily biodegraded oils, samples contaminated by oil-based drilling mud, and oil field solids such as tar mats, and deciphering the basin-filling history of migrated petroleum fluids (Murray et al. 1998; Russell et al. 2004). HyPy has also gained prominence in geobiological studies related to ancient biomarker detection, informing the evolution of microbial and animal life across Earth history (Love et al. 2009), and has been utilised for the detailed characterisation of the insoluble macromolecular material in carbonaceous chondrite meteorites (Sephton et al. 2005). Developed at the University of Nottingham (UK), HyPy has been available as a commercial system since 2010 (Fig. 17.1), manufactured and supplied by Strata Technology Ltd of Sunbury-on-Thames, UK (www.stratatec.co.uk)

We report results of a study examining controls on the degradation of chars produced at 300, 400 and 500 degrees C from radiocarbon-free wood, deployed for three years in a humid tropical rainforest soil in north Queensland, Australia. The chars were subjected to four treatments (i) no litter (ii) covered by leaf litter, (iii) covered by limestone chips to alter local pH, and (iv) covered by limestone chips mixed with leaf litter. Radiocarbon, stable isotope and proximate analyses indicate significant ingress of exogenous (environmental) carbon and mineral material, strongly correlated with loss of indigenous (char) carbon from the samples. While indigenous carbon losses over three years were generally <8% for the char produced at 500 degrees C char under any treatment, chars formed at lower temperatures lost 5-22% of indigenous carbon accompanied by ingress of up to 7.5% modern exogenous carbon. The data provide clear evidence of a direct link between the ingress of exogenous carbon, likely at least partly due to microbial colonization, and the extent of char decomposition. Failure to account for the ingress of exogenous carbon will lead to a significant under-estimate of the rate of char degradation. (C) 2016 Elsevier Ltd. All rights reserved.

We applied common (pH, elemental analysis, thermogravimetry) and less-common (infrared spectroscopy, GACS adsorption test, pyrolysis-GC-MS, hydrogen pyrolysis) analytical procedures to a set of biochars from Costa Rica (bamboo stalk, cacao chaff, sawmill scrap, coconut husk and orchard prunings feedstocks). The biochars were produced by high temperature combustion in a top-lit updraft stove (TLUD) and low temperature anaerobic charring in a retort (RET), the latter of which was heated by the gas that evolved from the TLUD. The RET biochars exhibit a smaller adsorption capacity, higher molecular diversity and larger proportion of thermolabile materials, because of the lower degree of thermochemical alteration (DTA) and therefore limited formation of the microporous polycondensed aromatic matrix typical of the TLUD biochars. Multivariate statistics showed that DTA, not feedstock composition, controls biochar organic chemistry. The TLUD biochars might be better candidates for soil amendment because of their adsorption capacities and will probably exert a more prolonged effect because of their chemical stability. The cross-comparison of the methods showed the complementarity of especially elemental analysis, GACS, thermogravimetry, hypy and pyrolysis-GC-MS.

Pyrogenic carbon (PyC; includes soot, char, black carbon, and biochar) is produced by the incomplete combustion of organic matter accompanying biomass burning and fossil fuel consumption. PyC is pervasive in the environment, distributed throughout the atmosphere as well as soils, sediments, and water in both the marine and terrestrial environment. The physicochemical characteristics of PyC are complex and highly variable, dependent on the organic precursor and the conditions of formation. A component of PyC is highly recalcitrant and persists in the environment for millennia. However, it is now clear that a significant proportion of PyC undergoes transformation, translocation, and remineralization by a range of biotic and abiotic processes on comparatively short timescales. Here we synthesize current knowledge of the production, stocks, and fluxes of PyC as well as the physical and chemical processes through which it interacts as a dynamic component of the global carbon cycle.

We produced 18 thermosequences of biochar from common feedstocks at ten temperatures from 300 to 900 °C to investigate their influence on carbon stabilization in biochar. Using hydrogen pyrolysis we were able to isolate the stable polycyclic aromatic carbon (SPAC) fraction that is likely to be resistant to mineralization on centennial timescales. SPAC formation was generally <20% of total organic carbon (TOC) at temperatures <450 °C and rises to >80% of TOC at temperatures above 600–700 °C depending on feedstock type. SPAC formation was retarded in feedstocks with high ash contents, and further retarded in those feedstocks when the final hold time at maximum pyrolysis temperature was reduced from one hour to 10 min. Given that aromatization of organic material in many feedstocks is usually completed by ca. 450 °C, the data suggests that a significant pool of aromatic biochar carbon exists in a ‘semi-labile’ form that may not be persistent on centennial timescales. For most feedstocks biochar yield and SPAC content are optimized at pyrolysis temperatures of 500–700 °C.

To better elucidate the reactions forming pyrogenic carbon (PyC) during pyrolysis, we investigated the carbon isotope fractionation trends in thermosequences for biomass types utilizing C-3 and C-4 photosynthetic pathways. PyC remaining after pyrolysis was treated using hydrogen pyrolysis to isolate the stable polycyclic aromatic carbon (SPAC) component and the semi-labile carbon component (PyCSL) was estimated from mass balance (the component that survived pyrolysis, but was not SPAC). C isotope fractionation trends as a function of pyrolysis temperature were determined for each of these three components (PyC, SPAC and PyCSL) relative to the C isotope composition of the bulk raw biomass. Although the isotope fractionation patterns for all materials were similar for total PyC, differences were noted between C-4 and C-3 biomass for isotope fractionation patterns of SPAC. The delta C-13 values of SPAC were higher than the original biomass for C-3 material, yet similar for C-4 material at formation temperature 300-700 degrees C. The delta C-13 values of PyCSL for all materials displayed distinct and progressively lower isotope composition relative to original biomass at higher temperature. The results, in combination with Fourier transform infrared patterns, indicated that the dominant source of SPAC is cellulose, and that lignin decomposes at higher temperature with very low delta C-13 MeO-rich lignin moieties preferentially surviving in PyCSL. The delta C-13 values of SPAC were 0.2 +/- 1.2% of the starting material, suggesting that this component might be used to determine the dominant source of PyC, although environmental mixtures of PyC in natural settings are more complex than those studied. (C) 2015 Elsevier Ltd. All rights reserved.

The aromatic carbon structure is a defining property of chars and is often expressed with the help of two concepts: (i) aromaticity and (ii) degree of aromatic condensation. The varying extent of these two features is assumed to largely determine the relatively high persistence of charred material in the environment and is thus of interest for, e.g., biochar characterization or carbon cycle studies. Consequently, a variety of methods has been used to assess the aromatic structure of chars, which has led to interesting insights but has complicated the comparison of data acquired with different methods. We therefore used a suite of seven methods (elemental analysis, MIR spectroscopy, NEXAFS spectroscopy, C-13 NMR spectroscopy, BPCA analysis, lipid analysis and helium pycnometry) and compared 13 measurements from them using a diverse sample set of 38 laboratory chars. Our results demonstrate that most of the measurements could be categorized either into those which assess aromaticity or those which assess the degree of aromatic condensation. A variety of measurements, including relatively inexpensive and simple ones, reproducibly captured the two aromatic features in question, and data from different methods could therefore be compared. Moreover, general patterns between the two aromatic features and the pyrolysis conditions were revealed, supporting reconstruction of the highest heat treatment temperature (HTT) of char. (C) 2014 Elsevier Ltd. All rights reserved.

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to evaluate the carbon chemistry of twenty-six biochars produced from eleven different feedstocks at production temperatures ranging from 350 °C to 600 °C. Carbon-13 NMR spectra were acquired using both cross-polarisation (CP) and direct polarisation (DP) techniques. Overall, the corresponding CP and DP spectra were similar, although aromaticity was slightly higher and observability much higher when DP was used. The relative size and purity of the aromatic ring structures (i.e. aromatic condensation) were also gauged using the ring current technique. Both aromaticity and aromatic condensation increased with increasing production temperature, regardless of the feedstock source. However, there were clear differences in these two measures for biochars produced at the same temperature but from different feedstocks. Based on a relationship previously established in a long-term incubation study between aromatic condensation and the mean residence time (MRT) of biochar, the MRT of the biochars was estimated to range from <260 years to >1400 years. This study demonstrates how the combination of feedstock composition and production temperature influences the composition of aromatic domains in biochars, which in turn is likely to be related to their recalcitrance and ultimately their carbon sequestration value.