Quantification for carbon footprint of agricultural inputs of grains cultivation in China since 1978

China is the largest country in grain production and consumption with the greatest emission of greenhouse gas (GHG) in the world. To learn the historical changes and regional differences in GHG emission of the major grain crop production can provide important references to the mitigation of GHG emission in the country and other similar countries. Therefore, we quantified the carbon footprints of rice (Oryza sativa L.), wheat (Triticumaestivum L.) and maize (Zea mays L.) production based on agricultural inputs in the country over the period of 1978-2012. The results showed that area-scaled carbon footprint of rice, wheat and maize production increased gradually from 1286, 937 and 895 kg carbon dioxide equivalent (CO2-eq) ha−1 in 1978-2682, 2978 and 2294 kg CO2-eq ha−1 in 2012, respectively, and the average increase rates for the three crops were correspondingly 41, 60 and 41 kg CO2-eq ha−1 a−1. During the last ten years, however, all the average yield-scaled carbon footprints of rice, wheat and maize decreased by 0.11 kg CO2-eq kg−1 10a−1. Chemical fertilizer contributed the largest ratio to the total GHG emission by 66, 68 and 76% for rice, wheat and maize, respectively. Significant increasing contribution ratio to the carbon footprint was found in the electricity used for crop irrigation. There were large differences in both the area- and yield-scaled carbon footprints among the cropping regions with the lowest GHG emission occurring in the major cropping regions. Our findings indicate a great potential to reduce GHG emission of grain production through optimizing the spatial layout of cropping region and enhancing chemical fertilizer use efficiency. Further efforts also need to be made on water-saving irrigation to decrease the electricity usage.