A two-year field measurement of methane and nitrous oxide fluxes from rice paddies under contrasting climate conditions

The effects of three irrigation levels (traditional normal amount of irrigation [NA100%], 70%, and 30% of the normal amount [NA70% and NA30%]) and two rice varieties (Oryza sativa L. Huayou14 and Hanyou8) on CH(4) and N(2)O emissions were investigated over two years under contrasting climate conditions (a ‘warm and dry’ season in 2013 and a normal season in 2014). Hanyou8 was developed as a drought-resistant variety. The mean seasonal air temperature in 2013 was 2.3 °C higher than in 2014, while the amount of precipitation from transplanting to the grain-filling stage in 2013 was only 36% of that in 2014. CH(4) emission rose by 93–161%, but rice grain yield fell by 7–13% in 2013, compared to 2014 under the NA100% conditions. Surface standing water depths (SSWD) were higher in Hanyou8 than in Huayou14 due to the lower water demand by Hanyou8. A reduction in the amount of irrigation water applied can effectively reduce the CH(4) emissions regardless of the rice variety and climate condition. However, less irrigation during the ‘warm and dry’ season greatly decreased Huayou14 grain yield, but had little impact on Hanyou8. In contrast, N(2)O emission depended more on fertilization and SSWD than on rice variety.