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 N ₂ O emission when it is discharged to agricultural drainage ditches. In this study, indirect N ₂ 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 N ₂ O emissions contributing an inter-annual mean flux of 6.56 ± 1.12 μg N m ^-2  h ^-1 and a mean indirect N ₂ O 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 N ₂ O 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 N ₂ O emissions varied with season, higher emissions occurred in summer and autumn. These seasonal variations were related to drainage water NO ₃ ^- -N concentration, temperature, and precipitation. Our results showed that intensive precipitation increased NO ₃ ^- -N concentrations and N ₂ O emissions, and when combined with warmer water temperatures, these may have increased the denitrification rate that led to the higher summer and autumn N ₂ O emissions in the studied agricultural drainage ditch.
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