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Soil incubations for model validation data sets and experiments to quantify the anaerobic soil volume fraction – Subproject P6 of the research unit 'Denitrification in Agricultural Soils: Integrated control and Modelling at various scales' (DASIM)
Project
Project code: TI-AK-08-PID1762
Contract period: 01.06.2016
- 31.05.2019
Purpose of research: Inventory & Assessment
To better predict gaseous nitrogen emissions from agricultural soils via microbial processes robust data on N2 emissions and oxygen depletion in soil are needed. Our task is to conduct laboratory studies in order supply these missing data. Denitrification is an anaerobic microbial process of successive reduction of nitrate (NO3-) and nitrite (NO2-) to molecular nitrogen (N2) through the following reaction steps: NO3- → NO2- → NO → N2O → N2. A significant fraction of nitrous oxide (N2O) produced in this process is not further reduced to N2 and constitutes the main emission source of this greenhouse gas from agricultural soils. Hence, our understanding and ability to quantify soil denitrification is crucial for mitigating nitrogen fertiliser loss as well as for reducing N2O emission. Robust denitrification data suitable to validate N2 fluxes in denitrification models are scarce due to previous methodical limitations 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)” (https://www.thuenen.de/de/ak/aktuelles-und-service/detail-aktuelles/news/detail/News/neue-dfg-forschergruppe-beschaeftigt-sich-mit-der-denitrifikation-in-agrarboeden/) investigates the denitrification process chain in agricultural soils using advanced analytical and molecular biologic methods as well as field studies and various modelling approaches. The aim is to investigate activity and regulation of denitrification in unpreceded spatial and temporal resolution and to use results to develop mathematical models from the micro-scale to the field scale and to improve existing simulation approaches. The anaerobic soil volume fraction, a major control of denitrification, is known to depend on the spatial distributions of gas diffusivity and respiration. However, estimating the anaerobic soil volume fraction has been hampered in the past by the difficulty to quantify its controls. Today, new and improved methods are available to fill those gaps. The objectives of our subproject P6 are to: - quantify N2, N2O and NO fluxes and the contribution of different N-transformation processes under variable denitrification control factors (organic C, mineral N, water potential, pore volume) as a basis to validate existing denitrification models. - provide data sets comprising as much as possible detail on activity and regulation (rates and types of N2 and N2O producing processes as well as the physical, chemical and microbiological control factors) as a basis to calibrate and validate new DASIM models. - determine the minimum averaging volume for N2 and N2O fluxes from arable soils. - determine the anaerobic soil volume fraction of DASIM soils under varying conditions. - visualize organic matter distribution in selected soil samples at the µ-scale. - test the feasibility to localize denitrification activity in selected soil samples at the µ-scale. Our objectives will be tackled in four parts: - We will use new and improved stable isotope approaches to provide denitrification data sets comprising as much as possible detail on activity and regulation as a basis to validate existing and calibrate new denitrification models that are applied and/or developed by other DASIM subprojects. - Incubations with increasing soil volumes under standardized conditions will be conducted to determine the minimum elementary volume of denitrification as a basis for upscaling. - In cooperation with other subprojects we will employ spatial gas diffusivity measurement and modeling as well as denitrification measurements at defined O2 status to obtain independent estimates of the anaerobic soil volume fraction. These approaches will be cross-validated and the most promising one will be used to calibrate the anaerobic soil volume fraction in the new denitrification models. - We will test to which extent the measurement of the µ-scale distribution of denitrification and its controls is feasible using nano-scale secondary ion mass spectrometry (NanoSIMS) and whether it is a suitable tool to further investigate µ-scale heterogeneity in phase 2 of DASIM. This test includes the measurement of organic matter distribution within selected soil aggregates and a new 15N tracer approach to locate nitrate consumption in aggregates.
Section overview
Subjects
- Soil science
- Process engineering
- Climate Change
Collaborative Project
FOR 2337: Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales
