Sewage irrigation increased methane and nitrous oxide emissions from rice paddies in southeast China
2009
Zou, Jianwen | Liu, Shuwei | Qin, Yanmei | Pan, Genxing | Zhu, Dawei
Greenhouse gas emissions from rice paddies under sewage irrigation deserve much attention since domestic sewage effluents are increasingly used for agriculture in developing countries. A field experiment was conducted to simultaneously measure methane (CH₄) and nitrous oxide (N₂O) emissions from rice (Oryza sativa L.) paddies under sewage and unpolluted river water irrigation in southeast China. The rice paddies were under a local typical water regime, which was characterized by flooding-midseason drainage-reflooding-moist intermittent irrigation but without water logging. Relative to unpolluted river water irrigation, sewage irrigation significantly increased CH₄ and N₂O emissions from rice paddies. Seasonal fluxes of CH₄ averaged 1.51mgm⁻² h⁻¹ for the plots irrigated by river water and 1.92mgm⁻² h⁻¹ for the plots irrigated by sewage. In contrast with river water irrigation, sewage irrigation increased CH₄ by 27% and 33% for paddy plots with and without chemical N addition, respectively. Under sewage irrigation, seasonal fluxes of N₂O-N averaged 26.79μgm⁻² h⁻¹ for the plots without N application and 74.07μgm⁻² h⁻¹ for the plots applied at the rate of 200kgNha⁻¹. Relative to river water irrigation, sewage irrigation increased N₂O by 68% and 170% for the plots with and without N application, respectively. The direct emission factor of fertilizer N for N₂O was estimated to be 0.71% for the rice paddies under sewage irrigation and 0.52% for the plots irrigated by river water. Besides direct N₂O emissions, N input by sewage irrigation induced substantial indirect N₂O emission from rice paddies. The results of the net GWPs from CH₄ and N₂O indicate that sewage irrigation would intensify the radiative forcing of rice paddies with midseason drainage and moist irrigation.
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