Exploring dissolved N 2 O characteristics and unearthing indirect N 2 O emission factors in the shallow groundwater of paddy and upland fields

• Published in: The Science of the total environment 2024-05, Vol.934, p.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
• ISSN: 1879-1026

Indirect emissions of nitrous oxide (N O) stemming from nitrogen (N) leaching in agricultural fields constitute a significant contributor to atmospheric N O. Groundwater nitrate (NO -N) pollution is severe in the Ningxia Yellow River Irrigation Area (NYRIA), coupled with high NO -N leaching, exacerbates the risk of indirect N O emissions from groundwater. Over two years of field observations, this study investigated the characteristics and interannual variations of dissolved N O (dN O) concentrations and indirect N O emission factors (EF ) in shallow groundwater. The research focused on three typical farmlands in the NYRIA, each subjected to six levels of N fertilizer application. The mean dN O concentrations in the groundwater of paddy, corn and vegetable fields were 5.17, 8.40 and 16.35 μg N·L , respectively. Notably, the dN O 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 dN O concentrations across various farmlands, showing statistically significant variation. However, differences in EF -A and EF -B within the same farmland were negligible. Denitrification was the primary process contributing to N O production in groundwater, with nitrification also played a crucial role in upland fields. Factors such as NO -N, NH -N, dissolved oxygen (DO), and pH critically influenced N O production. EF -B, which considers the NO -N consumption during denitrification processes in groundwater, was deemed more appropriate than EF -A for assessing the indirect N O emission in the NYRIA. The EF 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 EF -B in assessing indirect N O emissions, providing valuable insights for N management strategies in regions with high NO -N leaching. Minimizing N fertilizer application while ensuring crop yield, especially in upland fields, is beneficial for reducing N O emissions.