[Quantifying direct N2O emissions from paddy fields during rice growing season in China: model application].

Based on statistical analysis of field N2O measurements in rice paddies in China, the models on direct N2O emissions under different water regimes were established. After successes in model validation and input data verification, the models were used to quantify changes in direct N2O emissions from paddy fields during the rice growing season in mainland China between the 1950s and the 1990s. Due to increases in rice planting area and nitrogen input and changes in water regime, the models predicted that seasonal N2O-N emissions from rice paddies have increased from 9.55 Gg each year in the 1950s to 32.26 Gg N2O-N in the 1990s, which was accompanied by the increase in rice yield over the period 1950s-1990s. During the period 1950s-1990s, seasonal N2O-N emissions from rice paddies have increased, on average, at a rate of 6.74 Gg per decade. Seasonal N2O fluxes in rice paddies were estimated to be 0.32 kg x hm(-2) in the 1950s and 1.00 kg x hm(-2) in the 1990s, which accounted for 0.37% and 0.46% of the seasonal total N inputs, respectively. The uncertainties in N2O estimate were estimated to be 59.8% in the 1950s and 37.5% in the 1990s. Seasonal N2O emissions from rice paddies in the region of middle and lower Yangtze River contributed 51% -56% to its national total. In the 1990s, N2O emissions during the rice growing season accounted for 8%-11% of the reported annual total of N2O emissions from croplands in China, suggesting that paddy rice development could have contributed to mitigating agricultural N2O emissions in the past decades. However, seasonal N2O emissions would be increased given that saving-water irrigation and nitrogen inputs are increasingly adopted in rice paddies in China.