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Closing the carbon loop in sugarcane bioethanol : effects of filtercake biochar amendment on soil quality, leaching and carbon utilization

University of British Columbia

Commodity prices and rural development in Brazil are driving the rapid conversion of the Cerrado biome, a highly diverse ecosystem with nutrient-poor soils. The expanding agricultural footprint includes sugarcane for bioethanol production, which boasts one of the highest net energy yields of commercial biofuels. However, energetic assessments fail to consider ecosystem costs, including soil degradation and impacts on water quality through the release of organic effluents. This thesis examined the use of charcoal or biochar made of ‘waste’ biomass (filtercake) as a soil amendment to reduce soil carbon (C) loss and water quality impairment. The effect of biochar on the leaching of a liquid waste with high eutrophication potential, vinasse, was also examined. Soil amendment with filtercake biochar improved soil pH, cation exchange capacity (CEC), nutrient availability (P, K, Mg, Ca, Mg, Fe, Mn, and Zn), and water retention. Amendment with filtercake biochar rather than raw filtercake also greatly decreased CO₂ loss to rapid mineralization. Furthermore, biochar amendment decreased the loss of dissolved organic carbon (DOC) from a cultivated Ferralsol, with or without co-application of vinasse, through preferential retention of larger and more complex, humified DOC species. In contrast, biochar did not attenuate nitrate (NO₃-) leaching. Finally, δ¹³C isotope analyses were used to examine the effect of raw vs. pyrolyzed residues on C turnover in an uncultivated soil, which suggested that whereas raw filtercake appeared to be mineralized preferentially over native soil organic carbon (SOC), biochar application appeared to provoke mineralization of native SOC. Overall, this project suggest that filtercake biochar may represent a valuable opportunity to better manage solid and liquid organic agricultural wastes in bioethanol production, with the potential to close nutrient loops and improve soil quality. However, further work is required to better understand the effect of filtercake biochar on soil C turnover and its long-term stability.

Text

2014-09-19

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50410

Resource Management and Environmental Studies

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/