A method for screening the relative long‐term stability of biochar

Abstract

Biochar is being actively explored as a tool for long-term soil carbon sequestration. However, in order for this to be effective the long-term environmental stability of biochar must be assured. Here, we define and test an accelerated ageing method that seeks to reflect the oxidative nature of biochar degradation in soil. The method was applied to a systematic set of biochar samples produced from sugarcane bagasse, and a set of biochar samples produced from four different biomass sources. The stability of carbon in these samples was found to range between 41.6% and 76.1%, loosely correlating with biochar O : C ratio (r = 0.73). Increasing intensity of oxidative treatment eliminated more carbon. It also increased surface O : C ratio in a manner reported for naturally aged charcoal samples. The method effectively discriminated biochar produced under contrasting pyrolysis conditions and could be used as a proxy for environmental ageing of approximately 100 years under temperate conditions.

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

“…However, the properties of biochar non-stable fraction derived from various biomasses are different [14], and thus their effects on soil should be different. The labile fraction can have positive effects on soil microorganisms, increasing microbial biomass [32,51], with increase in CO2 emission from the decomposition of native soil organic carbon [22,52], or in some case negative effects on soil microorganisms with decrease [53] in CO2 emission. In fact, the microorganisms can utilize a number of labile biochar constituents as an energy source [22].…”

“…The labile fraction can have positive effects on soil microorganisms, increasing microbial biomass [32,51], with increase in CO2 emission from the decomposition of native soil organic carbon [22,52], or in some case negative effects on soil microorganisms with decrease [53] in CO2 emission. In fact, the microorganisms can utilize a number of labile biochar constituents as an energy source [22]. While some biochar associated labile components have biocidal activity [54], which may increase its stability against biotic decomposition.…”

“…A number of approaches have been proposed to assess stability and the carbon sequestering potential of different biochars, including solid state nuclear magnetic resonance spectroscopy (solid state 13 C NMR) [13,14], thermal analysis (thermogravimetry, TG) [15,16], molecular markers by means of pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) [17,18], benzene polycarboxylic acid method [19], O:C or H:C molar ratios [20,21], chemical oxidation [14,22], accelerated ageing technique [23], and hydropyrolysis (HyPy) [24,25,26].…”

Influence of feedstock properties and pyrolysis conditions on biochar carbon stability as determined by hydrogen pyrolysis

“…Such studies have demonstrated the existence of a labile fraction (general <5%) in most biochars that is re-mineralized over weeks to months, and a 'stable' fraction with an apparent residence time commonly, although not exclusively, measured in centuries [6e9]. It is possible that the 'stable' fraction identified in incubation studies actually represents at least two pools, a 'semi-labile' pool with a residence time measured in years to decades and a 'stable' pool with a residence time measured in centuries to millennia [10]. The ability to determine the proportion of carbon in each of these longer turnover pools is pivotal to being able to predict the proportion of carbon in a biochar that is likely to have a minimum residence time of a century [10].…”

Ageing of rice husk biochar along a freeze-thaw cycles

“…Nguyen [3] indicated that with the increasing of soil temperature, the loss rate of biological carbon increased, more incubation experiment showed that biochar character changes in its physical and chemical properties under different conditions [4]. The chemical and biological oxidation constantly changing the functional groups and chemical properties when biochar applied into soil [5]. It may also changed adsorption ability of biochar [6].…”