Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2011
Publication Date: 1/1/2012
Publication URL: http://hdl.handle.net/10113/55062
Citation: Fabbri, D., Torri, C., Spokas, K.A. 2012. Analytical pyrolysis of synthetic chars derived from biomass with potential agronomic application (biochar). Relationships with impacts on microbial carbon dioxide production. Journal of Analytical & Applied Pyrolysis. 93(1):77-84. Interpretive Summary: A variety of biochars were screened using an analytical technique called pyrolysis-gas chromatography-mass spectrometry (PyGCMS). This analytical technique allows the study of compounds, which traditionally could not be analyzed by gas chromatography. The biochars were heated separately under anaerobic conditions, and the gaseous products of this process were analyzed. With this analytical method, we observed a set of 38 compounds which represent various biomass products and compared this to the net CO2 respiration of the biochar amended soil. Overall, there was a relationship between the total release of compounds (yield) and the volatile matter content of the biochar. An important observation of this study was that biochar with high yields of proteins and cellulose-derived products resulted in the highest stimulation of CO2 respiration upon incorporation into soil. Therefore, the observed increase in CO2 production could be from the non-charred material and not truly representative of the biochar charred structured component. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved mechanisms of biochar additions to minimize greenhouse gas implications and improve soil carbon management.
Technical Abstract: A set of 20 biochar samples produced from the pyrolysis of different biomass feedstocks with potential applications as soil amendments were investigated by pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC-MS). The yields of 38 pyrolysis products representative of charred (e.g., benzene derivatives, PAHs, benzofurans) and partially charred biomass (e.g. derivatives of lignin phenols) were evaluated by Py-GC-MS. The estimated yields covered a wide interval (40-7700 µg g-1) and were correlated with volatile matter (VM; R=0.60). The proportion of pyrolysis products associated with charred materials ranged from 49 to > 99 % and was positively correlated with benzene/toluene ratios (R=0.68). The molecular distribution of partially charred materials reflected the original feedstock, with higher levels of protein fragments observed in samples with high initial nitrogen content. Both the abiotic and biotic production/consumption of CO2 was determined in original biochar incubated in water and soil-biochar systems. Large differences were observed in the net CO2 suppression/stimulation rates, with values between -50 to 2200 µg g(char)-1d-1 for biochar alone and biochar corrected rates from -19 to 690 µg g(soil)-1d-1 for amended soils. Biochars characterized by higher yields of proteins and cellulose-derived pyrolysis products (e.g., distiller grains, hardwood, mixed wood chips/manure) were associated with higher CO2 mineralization rates in the corresponding amended soils, particularly sugars (R = 0.73). These results suggest that the stimulation in CO2 production could arrive from the residual non-charred material, and not be a true indication of the charred material, which typically had no effect or minimal suppression.