TOWARD AN UNDERSTANDING OF THE ROLE OF BIOCHAR AS AN AGRO-ENVIRONMENTAL TOOL: POTENTIAL FOR CONTROL WATER RELEASE, BACTERIAL RETENTION, AND GREENHOUSE GAS EMISSIONS
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This dissertation aims to advance our knowledge on the relationship between biochar physico-chemical properties and its performance as a soil amendment. An emphasis was placed on understanding how the feedstock source and pyrolysis conditions influence biochar bulk and surface properties and what effects these properties have on greenhouse gas emissions, soil water retention, and movement of bacteria in sandy soils.Three lignocellulosic biomass feedstocks (poplar wood, pine bark, and pine wood) were used to produce biochars at six different pyrolysis temperatures (350, 400, 450, 500, 550, and 600oC). It was found that the content of volatiles, the oxygen to carbon (O/C) ratio, and hydrogen to carbon (H/C) ratio decreased linearly with temperature suggesting a gradual increase in aromatic structures and thermal recalcitrance. Pine bark-derived biochars had higher ash content than wood-derived biochars, and as the pyrolysis temperature increased, the ash content also increased.The surface study showed that biochars produced at low temperature (<500oC) retained some surface functionalities characteristics of the feedstock. The XPS and Boehm titration confirmed that most oxygenated surface functional groups (mainly; carbonyl, carboxyl and hydroxyl groups) are gradually removed as pyrolysis temperature increased. Oxidation by air at 250oC was able to introduce several oxygen functional groups onto the biochar surface. Particularly, the formation of carbonyl and carboxyl groups is facilitated in biochars produced at low temperature. The formation of these oxygenated functional groups contributes additional negative charges on the biochar surface.Upon biochar application to Quincy sandy soil, it was found that oxidized biochar held significantly more water and this is believed to be related to the content of oxygen functional groups and the pores structure. Oxidized biochars facilitated the transport of Escherichia coli through soil columns likely due to their negative surface charges that could repel bacteria that often carry an overall negative charge. Our results suggest that unoxidized pine wood-derived biochar was effective in reducing the transport of E. coli. Moreover, compared to the soil, biochar amendments did not affect the emissions of N2O but significantly reduced cumulative CO2 emissions (at 95% level of confidence).