In the present study, in-situ N2O and CH4 fluxes were quantified in organic agriculture. Trace gas fluxes were observed in winter wheat and spring wheat within an organic cropping system without livestock as well as in spelt and potatoes within an organic cropping system with livestock. Thereby, the impact of different manuring treatments based on the fermentation of cattle slurry and/or plant biomass in biogas reactors was investigated in comparison to the respective, common manuring practices. In the cropping system without livestock, green manures, intercrops, and crop residues were anaerobically fermented and used for manuring in contrast to the common mulching practice. In the cropping system with livestock, cattle slurry or cattle slurry and intercrops and crop residues were fermented and then applied as fertilizer in comparison to the common slurry and farmyard manure practice. The same crops and manuring treatments were investigated during three years (2002/2003 - 2004/2005). After 3.5 years of different manuring regimes, field soil samples were compared with respect to the microbial nitrogen and carbon metabolism.
In the laboratory, incubation experiments were carried out to assess the N2O and CH4 evolution from the fertilizers themselves, i.e. from raw slurry, fermented slurry, and fermented crop material under optimum conditions for denitrification. Furthermore, a three-week fertilization experiment was conducted in the greenhouse with spring wheat to investigate in more detail the impact of the different organic manures (raw slurry, fermented slurry, and fermented crop material) on the N2O emissions and the soil denitrifiers.
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