Indirect N₂O emissions with seasonal variations from an agricultural drainage ditch mainly receiving interflow water

Nitrogen (N)-enriched leaching water may act as a source of indirect N₂O emission when it is discharged to agricultural drainage ditches. In this study, indirect N₂O emissions from an agricultural drainage ditch mainly receiving interflow water were measured using the static chamber-gas chromatography technique during 2012-2015 in the central Sichuan Basin in southwestern China. We found the drainage ditch was a source of indirect N₂O emissions contributing an inter-annual mean flux of 6.56 ± 1.12 μg N m^-2 h^-1 and a mean indirect N₂O emission factor (EF_5g) value of 0.03 ± 0.003%. The mean EF_5g value from literature review was 0.51%, which was higher than the default EF_5g value (0.25%) proposed by the Intergovernmental Panel on Climate Change (IPCC) in 2006. Our study demonstrated that, more in situ observations of N₂O emissions as regards N leaching are required, to account for the large variation in EF_5g values and to improve the accuracy and confidence of the default EF_5g value. Indirect N₂O emissions varied with season, higher emissions occurred in summer and autumn. These seasonal variations were related to drainage water NO₃^--N concentration, temperature, and precipitation. Our results showed that intensive precipitation increased NO₃^--N concentrations and N₂O emissions, and when combined with warmer water temperatures, these may have increased the denitrification rate that led to the higher summer and autumn N₂O emissions in the studied agricultural drainage ditch.