Estimate of bacterial and fungal N2O production processes after crop residue input and fertilizer application to an agricultural field by 15N isotopomer analysis

•N2O emission increased after N application or potato crop residue input.•SP and δ15Nbulk were different between after N application and after residue input.•Nitrification and bacterial denitrification mainly produced N2O after N application.•Bacterial & fungal denitrification & nitrification produced N2O after residue input.•Real-time N2O isotopomer measurement is useful to estimate N2O production processes.

Nitrogen fertilizer and crop residue are important sources of N2O emission in agricultural ecosystems. This study aims to investigate N2O emission and microbial N2O production process after potato crop residue input and fertilizer application to an Andosol field. The experiment comprised crop residue treatments as follows: with residue (WR) and without residue (NR). We measured N2O emission, N2O isotopomer ratios (bulk N isotope ratios and intramolecular 15N site preference), and environmental parameters to estimate microbial N2O production processes. Comparative analysis of N2O isotopomer ratios and environmental parameters suggested that nitrification and bacterial denitrification were main N2O production processes after N application. Nitrifier denitrification would also contribute to N2O production after N application. In contrast, bacterial denitrification and fungal denitrification were important N2O production processes in the WR treatment after crop residue input, while nitrification also contributed to N2O production. Fungal denitrification was possibly important process during N2O peak after crop residue input. These findings reveal that real-time measurements of N2O isotopomers performed using a quantum cascade laser spectrometry system are useful for estimating microbial N2O production on a field scale.