Nitrous oxide emissions contribute up to 80% of the total greenhouse emissions from plant production. The release of N2O from soils generally increases with increasing availability of the substrates (mineral N) for the microbial N2O production. Therefore, N-fertilization induces enhanced N2O emissions. Similarly, lower uptake of mineral N due to infestation with fungal pathogens may stimulate N2O fluxes. Another important driver for the N2O release is soil aeration. Soil aeration is reduced with increasing soil moisture thus amplifying N2O release from denitrification. Due to the lower plant density in NOcsPS, we expect a higher soil moisture and consequently higher N2O emissions. Currently, there is an intense discussion on the potential of nitrification inhibitors to decrease N2O release from arable soils because they transiently decrease nitrate availability for denitrifiers.

Since some of the upper mentioned measures increase N2O emission whereas other measures decrease them, a clear effect of the "NOcsPS 2" system with its` adopted management measures on N2O release can`t be predicted and we therefore aim to quantify the overall effect to derive an emission factor for direct N2O emissions which than can be used for the assessment of the climate impact of the NOcsPS system.

Overall aim of the trace gas measurements is to derive an emission factor which than can enter GHG budgets or Life Cycle Analyses.

We test the following hypotheses:

1. The emission factor for direct N2O emissions in the NOcsPS 2 system differs from currently used emission factors (e.g. IPCC, Tier 1).
2. The reduction of the N-fertilization in NOcsPS 2 wheat decreases the annual N2O emission when compared to a conventional wheat system.
3. The lower plant density results in a higher soil moisture which increases the N2O emission from NOcsPS wheat when compared to a conventional system.
4. Infestation with Septoria tritici decreases uptake of mineral N and thus increases mineral N availability for N2O production when compared to conventional management.
5. Nitrification inhibitors can reduce annual N2O emissions and thus decrease the atmospheric burden in NOcsPS systems.

The N2O flux rates will be measured weekly over an entire year using the closed chamber method. Sampling will be complemented by additional measurements in periods with high N2O losses (N-fertilization period, rewetting of dry soil in summer, after thawing of soil in winter). Cumulative annual N2O emission will then be used to derive an emission factor for wheat in NOcsPS 2. We will also quantify the single effects of seeding technique, N-fertilization strategy (CULTAN), infestation of wheat with Septoria tritici, and a nitrification inhibitor on N2O emissions.

Simultaneously to gas sampling, we also take soil samples in order to determine mineral N and soil moisture in the topsoil. These data will be used for the parameterization of the trace gas fluxes.