Graduate Thesis Or Dissertation


Using Algal Biomass as a Fertilizer Public Deposited

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  • Algae can be used in a variety of wastewater systems to capture nutrients while fixing carbon dioxide from the atmosphere. I conducted field trials at three locations in Oregon with both corn and potato crops to assess the agronomic value and environmental impact of using the resulting algal biomass as a fertilizer. I compared the performance of algal biomass to a high-nitrogen (N) organic fertilizer, feather meal, and a conventional standard, urea. Soil nitrate, and petiole N, were measured throughout the season, and overall yield, produce N, and quality were measured at harvest. These data were used to calculate relative efficacy and resulting agronomic value. The emissions of carbon dioxide and nitrous oxide were measured through the course of the same field trial at two of the locations. These data were used to determine the amount of C added to the soil system from each fertilizer and the comparative gaseous losses from these sources of fertilizers. Several laboratory incubations were performed to help explain some of the variation and interactions found in the field trials. These data were used to calculate the N and carbon (C) mineralization rates of several subsamples of algal biomass in each of the three soils from the field trial. Although algal processing methods and nutrient media used can impact the overall mineralization rates of algal biomass added to the soil, algal biomass can be as effective at delivering N to the plant as both feather meal and urea per unit of N. In addition, roughly 50% of the C that was added to the soil as algal biomass was not respired as carbon dioxide by the end of the field trial. Therefore, it is likely to increase soil C, which is crucial in efforts to reinvigorate the biological community that support a functioning, healthy soil and could help to mitigate climate change. Considering the high degree of variability possible from algal biomass, it is recommended that material be characterized prior to application as a fertilizer and that site-specific edaphic and climactic characteristics be used in estimations of fertilizer application rates. I recommend the value of algal biomass be priced at a slight discount relative to feather meal on a price per unit of N basis.
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