Nitrous oxide emissions from production, storage and application of nitrogen enriched organic fertilizer

Plasma-based nitrogen (N) enrichment of organic fertilizers can improve agricultural resource efficiency and reduce fertilizer-related greenhouse gas (GHG) emissions. The method uses an electrically generated air plasma to produce reactive N that is absorbed by the organic fertilizer as nitrate (NO₃^-) and nitrite (NO₂^-). The enrichment process reduces the pH of the substrate, which reduces ammonia volatilization and inhibits microbial activity, which effectively prevents methane (CH₄) formation and denitrification during storage. However, the elevated content of reactive N increases the risk of chemical and microbial nitrous oxide (N₂O) formation. In this work, we determined a combined N₂O emission factor for the production, storage and field application of nitrogen enriched organic fertilizer to better assess its overall impact on fertilizer-related GHG emission. The N enriched organic fertilizer was shown to emit significantly more N₂O (1.8 % ± 0.48 % of total N) compared to the standard figure for untreated cow manure (1.0 % of total N), likely originating from chemical interactions of NO₂^- with organic compounds in the substrate and the soil. Despite the elevated N₂O emissions, the reduction in overall GHG was estimated to 72 ± 5.2 kgCO₂eq ton^-1 based on the Tier 2 methodology devised by the IPCC. A clear link was established between the NO₂^- content and N₂O emissions and a lower NO₂^- concentration was shown to reduce overall N₂O emissions by 45 %. Controlling the NO₂^- content is therefore a viable strategy to mitigate the N₂O emissions associated with nitrogen enriched organic fertilizers.