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Soil incubation study showed biogas digestate to cause higher and more variable short-term N2O and N2 fluxes than mineral-N

Today, a large share of mineral fertilizer is substituted by biogas digestates. Biogas digestates are known to promote N2O production, compared to mineral fertilizer. In particular, the initial phase following fertilizer application is crucial for the N gas release as N2O and also N2. How-ever, this period impact has been rarely investigated, especially not across various field sites.Thus, undisturbed soil cores from two fertilizer types (biogas digestate vs. mineral fertilizer) at five sites with different site characteristics were investigated in a short-term laboratory experiment under N2-free helium–oxygen incubation atmosphere. Across sites, biogas digestate soi lcores showed significantly higher absolute N2O fluxes compared to mineral fertilizer soil cores, even though this effect was dominated by samples from one site (Dornburg with the highest biogas digestate fertilization rate). Also relative N2O fluxes showed a similar tendency. On average, absolute and relative N2 fluxes differed between the two fertilizer types, while N2 fluxes were highest at the Dornburg site. A N2O/(N2O+N2) ratio of denitrification below or equal to 0.5 clearly highlighted the importance of N2O reduction to N2 for three of five the biogas digestate soil cores. Soil characteristics like bulk density and water-filled pore space as proxies for gas diffusivity in soil, as well as N availability (NO-3, NH+4), significantly affected the N2O and N2 fluxes from the biogas digestate soil cores. While this study presents data on short-term N2O and N2 fluxes, there is a need for further studies in order to investigate the dynamics, the duration of the observed effects and their significance at the field scale.



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