Indirect N 2 O 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 N2 O emission when it is discharged to agricultural drainage ditches. In this study, indirect N2 O 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 N2 O emissions contributing an inter-annual mean flux of 6.56 ± 1.12 μg N m-2  h-1 and a mean indirect N2 O emission factor (EF5g ) value of 0.03 ± 0.003%. The mean EF5g value from literature review was 0.51%, which was higher than the default EF5g value (0.25%) proposed by the Intergovernmental Panel on Climate Change (IPCC) in 2006. Our study demonstrated that, more in situ observations of N2 O emissions as regards N leaching are required, to account for the large variation in EF5g values and to improve the accuracy and confidence of the default EF5g value. Indirect N2 O 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 N2 O emissions, and when combined with warmer water temperatures, these may have increased the denitrification rate that led to the higher summer and autumn N2 O emissions in the studied agricultural drainage ditch.