Relationship Between Concentrations of N2O and NO3-N in Soil Under SRI Paddy Fields.

In rice paddy fields, anaerobic environment is developed in soil by flooding so that CH4 is generated due to the activity of methane producer (anaerobes bacteria). System of Rice Intensification (SRI) Farming is a rice cropping method with intermittent irrigation. The SRI becomes popular Southeast Asia in recent years. Attentions in recent years are beginning to be paid as the technology that can achieve an increase yield by reducing the resource input, such as rice seed, fertilizer, and irrigation water. Conducting SRI in a farm basis is not many so far in Japan. Although SRI is considered to suppress CH4 production, it may produce N2O as well by intermittent irrigation. The purpose of this study was to investigate the relationship between N2O and NO3-N concentrations in soil under SRI farming in Japan. Three treatments for water management practices were: (1) intermittent irrigation with 2-day drainage (2D), (2) intermittent irrigation with 4-day drainage (4D), and (3) continuous flooding except during the midseason drainage (CF). Soil gas concentrations were measured at 10, 20, 30 cm deep from the ground surface. Soil solution, collected at the depth of 40 cm, was measured for NO3-N concentration. Concentrations of N2O of soil gas and NO3-N of soil solution in the 2D and 4D treatments were higher than those in the CF treatment. Concentrations of N2O and NO3-N in the 4D treatment were slightly higher than those in the 2D treatment. Aerobic conditions made by intermittent irrigation may contribute to nitrification. Thus, the longer the drainage period was, the higher the concentrations of N2O and NO3-N.