Exploring dissolved N2O characteristics and unearthing indirect N2O emission factors in the shallow groundwater of paddy and upland fields

• Published in: The Science of the total environment 2024-07, Vol.934, p.173228, Article 173228
• Main Authors: Pan, Yongchun, She, Dongli, Ding, Jihui, Shi, Zhenqi, Abulaiti, Alimu, Hu, Lei, Huang, Xuan, Liu, Ruliang, Wang, Fang, Shan, Jun, Xia, Yongqiu
• Format: Article
• Language: English
• Subjects: Dissolved N2O; EF5g; Groundwater; Paddy fields; Upland fields
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.173228

Indirect emissions of nitrous oxide (N2O) stemming from nitrogen (N) leaching in agricultural fields constitute a significant contributor to atmospheric N2O. Groundwater nitrate (NO3−-N) pollution is severe in the Ningxia Yellow River Irrigation Area (NYRIA), coupled with high NO3−-N leaching, exacerbates the risk of indirect N2O emissions from groundwater. Over two years of field observations, this study investigated the characteristics and interannual variations of dissolved N2O (dN2O) concentrations and indirect N2O emission factors (EF5g) in shallow groundwater. The research focused on three typical farmlands in the NYRIA, each subjected to six levels of N fertilizer application. The mean dN2O concentrations in the groundwater of paddy, corn and vegetable fields were 5.17, 8.40 and 16.35 μg N·L−1, respectively. Notably, the dN2O concentrations in the shallow groundwater of upland fields exceeded those in paddy fields, with maximum levels in vegetable fields nearly an order of magnitude higher. Elevated N application significantly increased dN2O concentrations across various farmlands, showing statistically significant variation. However, differences in EF5g-A and EF5g-B within the same farmland were negligible. Denitrification was the primary process contributing to N2O production in groundwater, with nitrification also played a crucial role in upland fields. Factors such as NO3−-N, NH4+-N, dissolved oxygen (DO), and pH critically influenced N2O production. EF5g-B, which considers the NO3−-N consumption during denitrification processes in groundwater, was deemed more appropriate than EF5g-A for assessing the indirect N2O emission in the NYRIA. The EF5g of agricultural fields exhibited minimal sensitivity to N input but was significantly affected by other factors, such as the planting pattern. The study revealed the rationality of adopting EF5g-B in assessing indirect N2O emissions, providing valuable insights for N management strategies in regions with high NO3−-N leaching. Minimizing N fertilizer application while ensuring crop yield, especially in upland fields, is beneficial for reducing N2O emissions. [Display omitted] •Significant N2O variation across paddy, corn, vegetable fields in NYRIA.•Upland fields showed highest N2O, outpacing paddy fields.•Denitrification, nitrification key to N2O in groundwater.•EF5g-B better reflected N2O emission factors in NYRIA.•Planting pattern, not N input, majorly affected N2O emissions.