Reduction of Nitrogen Through Anaerobic Processes in Chinese Rice Paddy Soils

Comprehending the anaerobic nitrogen transformations, including denitrification, anaerobic ammonium oxidation (anammox), and anaerobic ammonium oxidation linked with iron reduction (Feammox) in soil, is essential for improving soil fertility and minimizing the environmental impacts of nitrogen loss. Despite this, research on anaerobic nitrogen transformations, particularly Feammox in paddy soil, is sparse. This study examined soil denitrification, anammox, and Feammox, along with their respective contributions to nitrogen loss in paddy soil at various depths, under different fertilization and irrigation treatments. It utilized 15N isotope labeling to investigate the limiting factors of these anaerobic nitrogen transformations and their interactions. The findings showed that denitrification rates ranged from 0.41 to 2.12 mg N kg−1 d−1, while anammox rates ranged from 0.062 to 0.394 mg N kg−1 d−1, contributing 84.3% to 88.1% and 11.8% to 15.7% of total soil nitrogen loss, respectively. Denitrification was identified as the predominant pathway for nitrogen loss across different soil depths. Fertilization and irrigation had more pronounced impacts on anaerobic nitrogen transformations than did soil depth, potentially affecting these processes through both abiotic and biotic pathways. This study identified significant correlations among the three types of anaerobic nitrogen transformations. These findings offer a theoretical foundation for optimizing nitrogen management strategies to mitigate losses in agricultural systems.