Nitrous oxide emissions from paddy fields under different water managements in southeast China

Abstract

Water management is recognized as one of the most important factors in regulating nitrous oxide (N2O) emissions from paddy fields. In China, controlled irrigation (CI) is widely applied because it has been proved highly effective in saving water. During the rice-growing season, the soil in CI paddy fields remains dry 60–80% of the time compared with soil irrigated by traditional methods. This study aims to assess N2O emissions from paddy fields under CI, with traditional irrigation (TI) as the control. The cumulative N2O emission from CI paddy fields was 2.5 kg N ha−1, which was significantly greater than that from TI paddy fields (1.0 kg N ha−1) (P < 0.05). Soil drying caused substantial N2O emissions. The majority (73.9%) of the cumulative N2O emission from CI paddy fields was observed during the drying phase, whereas no substantial N2O emissions were observed when the soil was re-wetted after the drying phase. More and significantly higher peaks of N2O emissions from CI paddy fields (P < 0.05) were also detected. These peaks were observed ~8 days after fertilizer application at water-filled pore spaces (WFPS) ranging from 78.0 to 83.5%, soil temperature ranging from 29.1 to 29.4°C, and soil redox potential (Eh) values ranging from +207.5 to +256.7 mV. The highest N2O emission was measured 8 days after the application of base fertilizer at a WFPS of 79.0%, soil temperature of 29.1°C, and soil Eh value of +207.5 mV. These results suggest that N2O emissions may be reduced obviously by keeping the WFPS higher than 83.5% within 10 days after each fertilizer application, especially when the soil temperature is suitable.