Background and Objective

Denitrification is the anaerobic microbial process through which nitrate (NO₃^-) and nitrite (NO₂^-) are reduced to molecular nitrogen (N₂) via the following reaction steps: NO₃^- → NO₂^-  → NO → N₂O → N₂. A significant fraction of the nitrous oxide (N₂O) produced within this process is not further reduced to N₂ and instead constitutes the main emission source of this greenhouse gas from agricultural soils. Hence, our understanding and ability to quantify soil denitrification is crucial for reducing N₂O emissions and nitrogen fertiliser loss.

Robust denitrification data suitable to validate N₂ fluxes in denitrification models are scarce due to the methodological complexities in collecting such data and the extreme spatio-temporal heterogeneity of denitrification. The coordinated DFG research unit „Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)” (http://www.dasim.de) investigates the  denitrification process chain in agricultural soils using advanced analytical and molecular biological methods as well as field studies and various modelling approaches. The aim is to investigate the activity and regulation of denitrification in unprecedented spatial and temporal resolution and to use the results to develop mathematical models from the micro-scale to the field scale, in order to improve existing simulation approaches.

Target Group

Scientific community

Approach

DASIM is a joint project, which is divided into eight different parts. At the Thuenen Institute of Climate-Smart Agriculture, we will address the questions in Subproject P6. Our tasks are to:

• determine the minimum soil averaging volume for N₂ and N₂O fluxes from arable soils.
• determine the anaerobic soil volume fraction of the DASIM soils under varying conditions. Although an essential control variable for denitrification, few studies have focused on quantifying anaerobic soil volume fraction, due to the difficulty in measuring its control factors. However, appropriate methods are now available.
• further develop and test the enhanced ¹⁵N gas flux method (¹⁵NGF+) in order to improve accuracy and better quantify the spatial distribution of denitrification activity.
• establish a field measurement system combining in situ analysis with ¹⁵NGF+.
• calibrate the isotopocule mapping approach using controlled lab incubations under an N₂-free atmosphere.
• quantify N₂ and N₂O fluxes, contributing processes and control factors in cropped soils to determine field-scale denitrification dynamics and use these as a basis for model calibration and validation.
• evaluate and further develop selected biogeochemical models using the measured data.

Our Research Questions

The questions to be addressed across the entire DASIM research unit are:

• How is the activity of denitrifiers and their community structure controlled at the micro-scale?
• How is denitrification affected and controlled by other simultaneously occurring N cycling processes?
• What controls the development of “hot spots” (i.e. specialised habitats) and “hot moments” (i.e. temporary hot spots) for denitrification activity?
• Do fundamental relationships exist between controls of denitrification at various scales (from micro- to meso- to field-scale)?
• Is it possible to predict denitrification of a given soil in response to atmospheric boundary conditions based on measurable structural and biochemical properties?

The questions addressed in our subproject (P6) are:

• How are N₂, N₂O and NO fluxes and their interaction with different N-transformation processes affected by physical, chemical and microbiological control factors at the field scale?
• What is the size of the minimum averaging volume for N₂ and N₂O fluxes from arable soils?
• How can we quantify the anaerobic soil volume fraction and to which extent can this measurement be used to improve denitrification models?

Links and Downloads

http://www.dasim.de/