Effect of pig slurry discharge frequency and combination with storage mitigation techniques on methane emission from house and storage

Introduction<br/>Methane emitted from manure in animal houses and outside storages amount to ca 25% of total Danish agricultural GHG emission (Andersen M.N. et al. 2023). Frequent removal of slurry from the slurry system in pig houses and transfer to outside storages has proven to be an effective and straightforward strategy to reduce slurry related house emission of methane (Dalby, F.R. et al.,2023) and is now required as the norm in Denmark. However, net methane emission from pig house and following outside storage period for slurry has been discussed as potential methane emission from storages will increase with increased transfer of slurry with a high organic matter to the storage due to low house retention time. Abatement technologies for storages and stored manure represents a large potential to reduce methane emission from animal-based production and ensure the sustainability of livestock production. This potential is increased with increased implementation of frequent transfer of slurry from pig houses to outside storages. In this study, the effect on storage emission and net house-and-storage emission of the combination of frequent in-house discharge and transfer of pig slurry to outside storages combined with in-storage mitigation techniques is tested in a year-round continuous measurement campaign.<br/><br/>Methodology<br/>A test facility with pilot scale (5-m3) covered storages was built to test different slurry management strategies and in-storage mitigation techniques on well-defined pig slurry in triplicate sets of storages. Slurry for the storages was produced by finisher pigs in two experimental pig sections with two pens with 15 finisher pigs in each pen. The slurry was added to the storages ad hoc in a spring-to-spring storage season as the slurry was discharged from the pig house. The slurry was discharged from the slurry system below the floor and transferred frequent (weekly) from one section and infrequent (every 5-6 weeks) from the other section to the outside storages (n=3). In addition, storage of frequently discharged slurry was combined with in-storage mitigation techniques in a treatment versus control setup of storages (n=3). Pig house sections and storages were equipped with a mechanical ventilation system with a diffuse air inlet and an outlet with a controlled exhaust air flow rate. During housing and storage period, methane was measured in in- and outlet air from the pig house sections and storages using cavity-ring-down spectroscopy (CRDS). Furthermore, air exchange and climatic conditions were measured, and slurry samples were collected for later analysis.<br/><br/>Results and discussion<br/>The last of four batches of pig and the associated emission from the house and storage periods, respectively will be finished in the coming spring. Initial preliminary results suggest a reduction in storage methane emission from slurry frequently discharged from pig houses and transferred to outside storage. The reduction of storage methane emission may be reinforced with additional reduction by combining with storage mitigation techniques. Preliminary results from the study on storage emission and net house-and-storage emission will be available for presentation at the conference.<br/><br/>Acknowledgements<br/>The authors acknowledge Y. M. Lemes, A. H. Vazifehkhoran, A. J. Ward, B. Kunnoth, P. W. Hansen, H. G. Christiansen and P.S. Nielsen for their valuable help during the experiment and the Ministry of Food, Agriculture and Fisheries of Denmark for funding, GUDP project no 34009-21-1939.<br/><br/>References<br/>Andersen M.N. et al., 2023. Viden- og forskningsbehov for forbedret grundlag for bedriftsspecifikke opgørelser af drivhusgasudledninger i landbruget. 69 sider. Rådgivningsrapport fra DCA – Nationalt Center for Fødevarer og Jordbrug, Aarhus Universitet. https://pure.au.dk/portal/da/publications/viden-og-forskningsbehov-for-forbedret-grundlag-for-bedriftsspeci<br/>Dalby, F., et al. 2023. Simple Management Changes Drastically Reduce Pig House Methane Emission in Combined Experimental and Modeling Study. Environ. Sci. Technol. 57, 3990–4002.