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Soil organic matter (SOM) content is one of the most important indicators of the sustainability of soil. To maintain sustainable soil utilization and management in fragile Hani terraced field, it is meaningful to investigate the effects of topography and land use type on SOM content. Descriptive statistics and geostatistics were used to analyze the data and the kriging method was applied to map the spatial patterns of SOM content. The results showed that the mean SOM content was 32.76 g/kg, with a variation coefficient of 40%. The SOM content was affected by elevation and land use type. As the increase of elevation, the SOM content in Hani terraced field also increased obviously. The SOM content in tea garden, which is almost at high elevation, was the highest in all six land use types, and the SOM content decreased in a following sequence: tea garden > paddy field > corn field > banana garden > cassava field > sugarcane field. In addition, at the same elevation, the paddy field had the highest SOM content compared with other land use types. All these results demonstrate that paddy field is the most efficient and suitable land use type for SOM conservation at high, middle or low elevations in the fragile Hani terraced field. In order to protect soil quality and maintain the sustainable agricultural development, it is necessary to maintain or even to enlarge the area of paddy field in Yuanyang county, Yunnan Province, China.

The area of rice production in Southern China is one of the most important farming regions in China, due to its great contribution to national food security. To assess the differences in carbon footprints (CF) of double rice production will benefit the achievement of low carbon agriculture. Base on the statistical data of crop yield and farmland investment of double rice production from 2004 to 2014, the spatiotemporal dynamics of CF and its composition of double rice in Southern China was estimated using the theory of CF and life cycle assessment method. The results showed that the CF of early and late rice in each province tended to increase, with the CF of early rice being higher than that of late rice. CF of early and late rice in Anhui were the highest (1000 kg CO 2 -eq·hm -2 ), and those in Fujian, Hubei and Hunan were the lowest (750 kg CO 2 -eq·hm -2 ). The highest component of CF in double rice was the production, transportation and utilization of fertilizers (60%), followed with the consumption of diesel. Progressive regression analysis showed that CF of double rice from 2004 to 2014 was mainly affected by diesel, compound fertilizer and K 2 O fertilizer. The analysis of net profit income showed that Hubei was a province with low-emission and high-yield, which was conducive to the sustainable development of low carbon agriculture. Given to the large transfer of rural labor from agricultural to non-agricultural sections and the development of mechanization, diesel and other mechanical inputs would increase rapidly in the future. Therefore, improving fertilizer utilization, mechanical and irrigation efficiencies in crop production would be the main approach to promote low-carbon agriculture in rice production of southern China.