Differential Responses of the Electron Transfer Capacities of Soil Humic Acid and Fulvic Acid to Long-Term Wastewater Irrigation

Wastewater irrigation is used to supplement agricultural irrigation because of its benefits and freshwater resource scarcity. However, whether wastewater irrigation for different years affects the electron transfer capacity (ETC) of natural organic matter in soil remains unclear. The composition of soil humic substances (HS) is highly complex, and the heterogeneity of the effects of soil humic acid (HA) and fulvic acid (FA) on ETC is poorly understood. In this study, we separately evaluated the responses of the electron-accepting capacity (EAC) and electron-donating capacity (EDC) of soil HA and FA in agricultural fields to different wastewater irrigation years. Results showed that the EAC of HA and FA increased to a certain extent and significantly increased with the increase in wastewater irrigation years. When wastewater irrigation lasted for 56 years, the EAC of HA showed a higher increment (5.9 times) than that of FA (2.2 times). The EDC of soil HA and FA, alternatively, decreased. Specifically, the EDC of HA gradually decreased starting from 29 years of wastewater irrigation, whereas the decrease in the EDC of FA exhibited no clear pattern in relation to wastewater irrigation years. The irrigation of farmland with wastewater for different years could affect sucrase and phosphatase activities in soil by altering the content of soil organic matter and total N, thereby modifying the chemical structure of HA and FA and ultimately resulting in the different trends of the changes in their ETC. The results of this research provide a foundation for a deepened understanding of the role of HS in agricultural soil environments under long-term wastewater irrigation and offer practical insights for making management decisions regarding farmland soil environments under wastewater irrigation over nearly a century.

Keywords: Soil humic substances, Redox activity, Wastewater irrigation years, soil enzyme activity

Suggested Citation: Suggested Citation

Gao, Yiman and Zhang, Yuan and zhang, Yifan and Chen, Shuhe and Su, Jing and Xi, Beidou and Tan, Wenbing, Differential Responses of the Electron Transfer Capacities of Soil Humic Acid and Fulvic Acid to Long-Term Wastewater Irrigation. Available at SSRN: https://ssrn.com/abstract=4689364 or http://dx.doi.org/10.2139/ssrn.4689364