Epsilon Open Archive

Abstract

Organic fertiliser handling contributes to greenhouse gas emissions. Through storage and field experiments, this thesis examined strategies to reduce emissions of nitrous oxide (N₂O) and methane (CH₄) from storage and after land application of cattle slurry (CS) and sewage sludge (SS). Non-digested CS without a roof (1) and digested CS without (2) or with a roof (3) were stored during three months in summer and winter. Mesophilically digested SS without cover (1), with cover (2) or treated with ammonia (NH₃) and with cover (3), and thermophilically digested SS with cover (4), were stored during one year. CS treatments (1) and (3) were applied to soil in spring or in autumn. SS treatments (3) and (2) were applied in spring and autumn, respectively, and were either incorporated into the soil immediately or after four hours. A life cycle assessment was conducted to assess the impact on global warming potential, acidification potential, eutrophication potential and primary energy use of different management strategies for SS.

Digested CS had significantly higher CH₄ emissions than non-digested CS during summer storage. Using a roof in summer decreased CH₄ and increased N₂O emissions significantly, but these cancelled each other out on a global warming basis. Emissions of N₂O and CH₄ were small during winter storage and after land application. Treatment with NH₃ significantly reduced N₂O emissions from SS during storage and tended to lower CH₄ emissions. Thermophilically digested SS had more air-filled pores during storage and emitted significantly more N₂O than other treatments, but had the lowest CH₄ emissions. Emissions of N₂O after SS application to soil were low, but stimulated by wet soil and precipitation, while CH₄ emissions were negligible, with no differences between immediate and delayed incorporation. The LCA revealed that shorter storage time and covered storage could mitigate the environmental impact from SS management. NH₃ treatment generally reduced negative impacts on environment categories except for primary energy use, which was highest for this treatment. A combination of autumn and spring application was preferable to autumn-only application for most treatments through lowering total storage time.