In this paper, we discuss different methods to calculate greenhouse gas field emissions from fertilization and soil carbon changes to be integrated into Carbon Footprint (CFP) of food and biomass products. At regional level, the simple Tier 1 approach proposed in the IPCC (2006a) AFOLU guidelines is often insufficient to account for emission variability which depends on soil type, climate or crop management. However, the extensive data collection required by Tier 2 and 3 approaches is usually considered too complex and time consuming to be practicable in Life Cycle Assessment. We present four case studies to compare Tier 1 with medium-effort Tier 2 and 3 methodologies. Relevant differences were found: for annual crops, a higher Tier approach seems more appropriate to calculate fertilizer-induced field emissions, while for perennial crops the impact on CFP was negligible. To calculate emissions related to soil carbon change higher Tiers are always more appropriate.
