Agricultural productions are very sensitive to climate change. Controlling agricultural greenhouse gases emissions is not only a key issue in China's efforts to address global climate change, but also an essential part of the country's drive to accelerate the shift in its agricultural development modes. For agriculture, crops and soils have substantial carbon sequestration potential. However, agricultural production has induced large amounts of carbon emissions due to the usage of chemical fertilizers, pesticides, machineries and other agricultural materials. Hence, developing low-carbon agriculture has largely depended on increasing carbon efficiency of crop production. Previous studies on carbon efficiency of agricultural production had concentrated on the effects of agricultural management and planting structure on carbon efficiency. However, studies on the spatial and temporal variations in regional agricultural carbon efficiency had remained extremely unavailable, especially the underlying driving factors. As the main grain production base in Jiangxi Province, Poyang Lake Eco-Economic Region has been promoted as a national strategy in 2009. In this study, carbon input and output data of major crop productions in Poyang Lake Eco-Economic Region were obtained from Jiangxi statistical yearbooks for 2001-2011. Subsequently, carbon production efficiency, carbon economic efficiency and carbon ecological efficiency of crops were calculated at county scale. The objectives of this study were (1) to clarify the spatial and temporal patterns of carbon efficiencies of various crops in Poyang Lake Eco-Economic Region, and (2) to discuss the underlying driving factors of the spatial-temporal variations. Results showed that carbon production efficiency of crops varied from 9.27 to 10.16 kg.kg -1(CE) during 2000-2010. The variation pattern could be separated into three phase as "decline phase (2000-2003), smooth phase (2004-2007) and increasing phase (2008-2010)". Carbon economic efficiency of crops fluctuated but followed a downward trend with a range of 10.73 to 9.25 Yuan.kg -1 (CE) in 2000-2010. Carbon ecological efficiency of crops ranged from 1.76 to 1.94 kg(C).kg -1(CE) in 2000-2010. This was further divided into three phases as continuous declining phase (2000-2003), smooth development phase (2004-2007) and continuous growth phase (2008-2010). Furthermore, carbon efficiency of crops showed a significantly characteristic spatial concentration in Poyang Lake Eco-Economic Region; where high carbon efficiency zones were mainly concentrated in the southeast of the region for most of the years. However, low carbon efficiency zones were mainly concentrated in the counties around Jiujiang City. In the case of stable carbon input, carbon production efficiency of crops was mainly influenced by the level of agricultural development and crop yield. Carbon economic efficiency was mostly controlled by grain production and pricing system. The ecological efficiency of carbon was mainly driven by agricultural carbon output. Most counties in Poyang Lake Eco-Economic Region were agricultural carbon-sinks, which needed to be maintained by sustainable low-carbon agricultural developments.
