Research Publications

Urban farms, particularly those utilizing vertical space and hydroponics, have the potential to address many challenges of the existing food system. The use of organic inputs in hydroponics can conserve dwindling non-renewable resources and mitigate greenhouse gas (GHG) emissions associated with inorganic nitrogen (N) fertilizer production and use. The study compared plant growth using organic liquid fertilizer (OLF) from insect and chicken waste in a two-step aerobic bioreactor. Basil (Ocimum basilicum) plants were grown with an inorganic fertilizer control and a novel OLF at two separate locations. In the first part of the study, plant yield, nutrient uptake and tissue elemental composition were used to validate the functional equivalency of OLF versus inorganic fertilizer. The second part of the study used these results to conduct a life-cycle assessment (LCA) to quantify GHG mitigation potential of the novel OLF. N-mass balance showed a liquid nitrogen conversion rate ∼40% for the bioreaction. Solid output from the bioreaction contained approximately 35% of the initial N. N-gaseous loss was approximately 25% of total N-input. Because the nature of gaseous N-loss was unknown, LCA modeled different scenarios varying the percent of gaseous N-loss as N₂O, as it is the only nitrogen-based gas with appreciable global warming potential. Models showed that N₂O leakage during bioreaction must be below 5% of total N-input for OLF to mitigate GHG emissions associated with fertilizer usage in urban hydroponic production. Further studies should focus on direct quantification and characterization of gaseous N-loss during this type of bioreaction.