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Flux measurements of CO2 exchange is carried out continuously at the experimental site near Ll. Valby using the eddy correlation approach. Flux measurements of N2O emissions is carried out semi-continuously (daily) by using an automatc gas-sampling system coupled to automated flux chamber (occasionally measurements of CH4 are also included)
Automatic opening and closing soil cover box coupled to an automated headspace gas sampler. The samples are stored in vials for subsequent analysis by gas chromatography.
In addition to the field gas flux measurements controlled experiments are carried out to test experimentally the impacts of management (e.g. cutting, inorganic and organic fertilisation, grazing) on the processes controlling the trace gas fluxes. This information is a prerequisite for the development of mechanistic models and for scaling-up fluxes to national and regional scales.
The project recieves funding form the EU and is part of the transeuropean project "GREEN’GRASS"
Contact persons: Kim Pilegaard (EU principal investigator and responsible for micrometeorological CO2 measurements), Per Ambus (N2O, CH4 and soil N turnover measurements) and Teis Mikkelsen (plant physiology)
Dinitrogen fixation and nitrous oxide production in organically managed grass-clover pasture (DINOG).
In organic as well as conventional dairy farming, grass-clover pastures are an important component of the cropping system, and these pastures are expected to have a high level of nitrogen in the root zone due to the fixation of atmospheric dinitrogen (N2).
Worldwide, 186 countries have signed the United Nations Framework Convention on Climate Change, and these countries are all committed to make national budgets for emissions of greenhouse gases. The Intergovernmental Panel on Climate Change (IPCC) has made guidelines to be used for calculating the emissions. According to the IPCC guidelines, inventories for N2O emissions from agricultural soils should be based on the assumption that 1.25 % of added nitrogen is emitted as N2O. This emission factor is used for all N inputs although the factor relies on experiments with fertiliser and manure, only. The emission factor for biological fixed nitrogen may be different from 1.25 %, however knowledge is very sparse.
Emission of N2O may depend on the intensity with which dinitrogen fixed by clover is recycled in the plant soil system. The grass-clover pastures are typically grazed for a significant part of the year and nitrogen depositions from grazing cattle’s excreta are at risk of being lost to the atmosphere or lost via leaching. Thus far, however, there have only been a few detailed estimates of total N2O emissions from grassland livestock production systems, and understanding of the factors controlling N2O emissions remains unsatisfactory.
Main objectives of the project are to:
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develop a method to measure in vitro N2 fixation and N2O production from grass-clover
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establish the fraction of recently fixed N, which is released to the soil and taken up by companion plants as well as the fraction which is emitted as N2O (the emission factor)
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identify the microbial processes responsible for the production of N2O and investigate how these are influenced by urine deposition and the relationship with rhizosphere C mineralization.
During 2002 an small growth cabinet has been developed and used to study the N2 fixation in grass-clover grown in pots.
Grass-clover in pots for incubation in 15N2-labelled atmosphere in a full-control growth cabinet, based on modified commercial freezer
Small intact monoliths of grass-clover pasture has been cross-labelled with 15N (K15NO3 ´ (15NH4)2SO4). Following labelling the evolved N2O is collected and examined for 15N in order to identify and quantify the process responsible for N2O production. This information is needed to parameterize the whole-farm N-cycling model (FASSET) in coorporation with DIAS.
Co-operating institution: Danish Institute of Agricultural Sciences |