Origin of positive δ13C of emitted CO2 from soils after application of biogas residues

► Soil-emitted CO2 had a positive δ13C of +23.6‰PDB after applying biogas residues. ► Inorganic carbon of biogas residues (BGR-IC) had δ13C of over +35‰PDB. ► BGR-IC made a significant contribution to soil-emitted CO2 in the initial stage. ► 13C-enriched BGR-IC was caused by strong fractionation in the biogas production.