| Methane (CH4) is one of the most important greenhouse gases. Irrigated Paddy Field is a major atmosphere emission source, accounting for about12%-26%of global anthropogenic emission. China is a large rice planting country, studying on methane emission of China and its driving factors will be helpful to make reasonable mitigation methods. This study constructed model of the impact factors which were geographic location, pH, soil C:N ratio, fraction of clay and sand in the soil, rate of organic carbon input, irrigation regime, synthetic nitrogen application, temperature by established methane emission of paddy field, and further quantitative analysis of different factors on methane emissions from rice paddy. To address the spatial and temporal distribution characteristics of methane (CH4) emission from Chinese rice paddies and to quantify the relationship between CH4emission and driving factors associated with environment and field management in different rice cropping systems.By searching literature databases, we obtained117articles published since1987that related to the field measurements of CH4emission in different regions. A total of696datasets of the seasonal amount of CH4emission or the mean flux of CH4emission over a growing season measured at70sites were extracted from these articles. ANOVA, correlation analysis and stepwise regression were used to investigate the spatial characteristics of CH4emission and driving factors. Major results presented as follows:1. By analyzing495datasets of the seasonal amount of CH4emission according with conventional management. The result showed that:The mean and standard error of CH4emission from single rice, early-rice and late-rice cropping system were383.5+31.1,234.3±16.8and361.8±25.0kg·hm-2, respectively. Methane emission from the single rice in southwest China is the highest, approximately being1.3,1.2and3.3times higher than those in north, central and northeast China. In double rice cropping system, CH4emission from the early-rice and the late-rice in central China is approximately160%and90%higher than those in south China (Guangxi and Guangdong Province). Under the same or similar fertilization and irrigation management, there are significant differences of CH4 emissions between late rice and early rice.2. There is a significant positive correlation between CH4emission and the input of organic carbon, while CH4emission was found to be negatively correlated with the rate of synthetic nitrogen application and soil pH. CH4emission from the single rice system declined with increasing latitude, longitude and soil total nitrogen. By contrast, CH4emission increased from south to north in the double rice system, and increased with soil total nitrogen in the late-rice system. The proportion of drainage was more than50%of total for single rice, early rice and late rice; Flood accounted for83.8%in South-west Single region. Drainage accounted for about80%in Guangdong-guangxi double rice regions. CH4emissions from rice fields were significantly different (p<0.05) in different irrigation management. CH4emission of flood paddy presented approximately0.75-1.85times higher than drainage. The average of Nitrogen Fertilizer was147kgN·hm-2in Chinese rice paddies in recent two decades, and ranged from75to150kgN·hm-2. The highest N fertilition occurred in North China single region, which was188kgN·hm-2; and south-west is the least (123.4kgN·hm-2). In comparison with the CH4emission from no nitrogen paddies, the application of nitrogen reduced methane emission of rice paddies. The extent of decrease ranged from44%to47%in drainage paddies, and14%to62%in flood paddies. The addition of nitrogen showed no significant effect on methane emission. With the increment of exogenous organic carbon, CH4emission enhanced more significantly; Green manure, farm manure, the straw biogas residues and compost have different conversion of exogenous carbon for CH4emission in similar conditions, the range of Conversion of exogenous carbon is from6.1%to26.2%.3. The spatial variability in seasonal amount of CH4emission for the single rice can be well quantitatively described by a linear combination of six variables (R2=0.72, p=0.000, n=241), including soil C:N ratio, irrigation regime, rates of organic carbon input and synthetic nitrogen application, etc. For the early-rice, the spatial variability in CH4emission was quantitatively determined by a linear combination of five variables (R2=0.35, p=0.000, n=121), including soil C:N ratio, irrigation regime, rate of organic carbon input, etc. A linear combination of six variables, including soil C:N ratio, fraction of clay in the soil, rate of organic carbon input and so on, determined the spatial variability in CH4emission for the late-rice system (R2=0.47, p=0.000)4. The proportion of the hybrid rice for the South-west and the Central China late rice region was86.8%and50.55%, respectively. The other regions are mainly conventional rice varieties. In a similar condition, methane emissions from the Hsien Rice are about1.22to1.92times the CH4emissions of Japonica Rice; CH4emission of Conventional hsien rice is about40%more than conventional japonica rice. We got the hybrid rice methane emissions slightly higher than conventional rice varieties. We could finally conclude that:1. The seasonal amount of CH4emission per unit area from rice paddy ranks in a descent order of single rice, late-rice and early-rice in China, but no significant difference existed between the single and late-rice. CH4emission in southwest China is significantly higher than those in other single rice regions. For the double rice system, CH4emission in central China is significantly higher than those in south China. Linear multi-regression models taking into account environment and field management could be used to explain the spatial variability in seasonal amount of CH4emission for all rice cropping systems, and the explanatory capability of model for the single rice is much higher than that for the double rice system.2. The application of nitrogen reduced methane emissions from rice paddies. There was positive correlation between exogenous organic carbon input and methane emission (p=0.005) when the carbon input lower than2t·hm-2; In similar conditions, Conversion of exogenous carbon from different organic fertilizers was different, which range from6.1%to26.2%.At the same time, the organic fertilizer had different contribution rates under the flood and drainage. Methane emissions of hybrid rice were slightly higher than conventional rice varieties, the average CH4emissions of hsien rice is40%higher than japonica rice. |
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