Preface. 1. Aspects Related to Organic Matter Turnover. 2. Aspects Related to Fertilization: Uptake, Availability, Efficiency, Techniques. 3. Aspects Related to Biological Fixation. 4. Aspects Related to Nitrogen Advice Systems and N-Balance. 5. Aspects Related to Modelling. 6. Aspects Related to Ammonia Volatilization. 7. Aspects Related to Nitrification and Denitrification. 8. Aspects Related to Leaching. 9. Aspects Related to Methodology.