Abstract
AbstractToday, 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. However, 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 soil cores 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 ( , ), 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.
Highlights
Gaseous nitrogen (N) emissions from agricultural fields are considered problematic both from an agricultural—in terms of N efficiency—as well as from an environmental perspective (Cameron et al, 2013)
Biogas digestate soil cores 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)
Despite the limited scope of this experiment, this study provides valuable insights into short-term N2O and N2 fluxes as well as the N2O/(N2O+N2) ratio of denitrification following the initial phase of fertilizer application from different field sites
Summary
Gaseous nitrogen (N) emissions from agricultural fields are considered problematic both from an agricultural—in terms of N efficiency—as well as from an environmental perspective (Cameron et al, 2013) This is the case for nitrous oxide (N2O), which is highly relevant due to its global warming potential (IPCC, 2013), while it is expected to be the single most important ozone-depleting substance throughout the 21st century (Ravishankara et al, 2009). While for NH3 there is already a lot of information about the impact of N fertilization available (e.g., Wolf et al, 2014; Seidel et al, 2017; Pietzner et al., 2017), for the other important gas N2 there is still very limited information on fertilizer-related N2 losses This is the case for the application of organic fertilizer in form of fermentation residues, often called biogas digestates (BD), which are increasingly used as organic amendments in agriculture (Charles et al, 2017). The modified O2 availability in combination with high amounts of available organic C provided by BD enhances soil respiration
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