EGU21-12347
https://doi.org/10.5194/egusphere-egu21-12347
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Flux measurements of NHx and NOy with a dual-channel converter above an intensively managed grassland on peat

Pascal Wintjen1, Jeremy Rüffer1, Liv Sokolowsky1, Christof Ammann2, and Christian Brümmer1
Pascal Wintjen et al.
  • 1Thünen Institut, Agrarklimaschutz, Braunschweig, Germany (pascal.wintjen@thuenen.de)
  • 2Swiss Federal Research Station Agroscope, Zürich, Switzerland

We designed a fast-response two-channel converter called NOy-TRANC for eddy covariance measurements of reduced and oxidized reactive nitrogen compounds (Nr). It is a combination of the Total Reactive Atmospheric Nitrogen Converter (TRANC), which converts all reactive forms of nitrogen (ΣNr), except for nitrous oxide (N2O) and molecular nitrogen (N2), to nitrogen monoxide (NO), and a heated gold catalyst, which converts NOy to NO. NOx, which is the sum of NO and nitrogen dioxide (NO2), and higher oxidized nitrogen compounds are described by the term NOy. The NOy-TRANC is coupled to a two-channel chemiluminescence detector (CLD) for measuring NO. Due to a high sampling frequency and a fast response time, the system meets the requirements for flux calculation based on the eddy-covariance method. With this setup, a separation of ΣNr fluxes in reduced and oxidized nitrogen can be done.

We conducted flux measurements at a typically deeply drained, intensively managed grassland site on peat in an intensive dairy region in Northwest Germany for one year. ΣNr concentration was 12.4 ppb and NOy concentration was 6.3 ppb on average. We observed mostly emission fluxes at the site after the first fertilization in early spring. The winter month were characterized by slight nitrogen dry deposition. Monthly median of ΣNr fluxes ranged from -8 to 57 ng N m-2s-1 with the exchange being enhanced during summer. We found that ΣNr and NOy dry emission were comparatively higher under dry conditions, i.e., low air humidity and soil moisture. The emission factors of applied nitrogen after the respective fertilization released as NHx can reach up to 2.0%.

Site management included five fertilization events and five grass cuts. The first fertilization event was at the end of March starting with mineral fertilizer followed by organic fertilizer a week later.  The fertilization scheme was the same for second and third event, but approximately two days were between the application of the fertilizer types. The second fertilization was at the end of May, subsequent fertilizations were done in intervals of 4-5 weeks. Only for the fourth and fifth event, organic fertilizer was used. Organic fertilizer was injected in slits made by v-shaped discs, mineral fertilizer was spread on the soil surface. The emission factor was lower after the first fertilization event compared to events in summer probably indicating a beginning nitrogen saturation after the first fertilization.

Our study demonstrates the application of a novel measurement technique for the determination reactive nitrogen compounds and gives insight into the exchange characteristics of reactive nitrogen under a common agricultural management.

How to cite: Wintjen, P., Rüffer, J., Sokolowsky, L., Ammann, C., and Brümmer, C.: Flux measurements of NHx and NOy with a dual-channel converter above an intensively managed grassland on peat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12347, https://doi.org/10.5194/egusphere-egu21-12347, 2021.

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