Soil tillage affects several soil physical and biochemical parameters of soil organic matter turnover, which can significantly influence the soil-crop system. The practice of reduced soil tillage, known as conservation tillage or non-inversion tillage, is common in America, Australia and South Africa, but adoption of this practice in Europe has been much slower, partly due to a poor understanding of the effects of this practice on productivity and environmental conditions for European conditions. It is important that these effects are quantified for short- and long-term time scales. To address these issues, a field experiment with different soil tillage intensities in typical cereal based crop rotation was initiated in 2002 in Denmark and was completed with scenario modeling. The objective of the study was to assess effects of different soil tillage intensities on the emissions of soil organic matter, CO₂ and N₂O and N leaching from arable cropping systems over the whole year. The FASSET model was updated with the tillage component and used (www.fasset.dk). The CN-SIM model for soil organic matter turnover, with is more advanced than the Daisy model in C and ¹³C development at the short- and long-term time was parameterized for soil tillage effects based on available experimental data. Additionally, the updated plant residue model was included in FASSET and parameterized on available experimental data. The experimental measurements were taken in three soil tillage treatments: CT - conventional tillage, RT - reduced tillage and DD - direct drilling. Scenarios, organized for those soil tillage treatments, were done for typical Danish climates and soils with differences in residue input. It was found in scenario analysis that reductions in both tillage and fallowing may increase soil organic C and that the corresponding differences in CO₂ emission between the soil treatments after 2-3 years after initiation of experiment could be solved with the correct parameterization of the model. It was found that microbial component of the model was playing on of the key-roles at the short-term turnover, whether on the long-term humification and vertical transport was under consideration. Simulated and measured changes in soil C and CO₂ emission for the same soil tillage treatments have had the similar magnitude. Additional test-calculations were done with data from Finland, Belgium, France and US. These modeling issues require further research.

Keywords: CO₂, soil organic matter, reduced tillage, ploughing, plant residues