Abstract: With reference to the situation of nitrogen fertilization in 2003 and the recommendations from agricultural experts on fertilization to different crops, two scenarios, namely, ‘current situation’ and ‘fertilization as recommended’, were set for estimating the current and potential carbon sequestration of China’s cropland soil under nitrogen fertilization. After collecting and analyzing the typical data from the long-term agricultural experiment stations all over China, and based on the recent studies of soil organic matter and nutrient dynamics, we plotted China into four agricultural regions, and estimated the carbon sequestration rate and potential of cropland soil under the two scenarios in each province of China. Meanwhile, with the data concerning fossil fuel consumption for fertilizer production and nitrogen fertilization, the greenhouse gas leakage caused by nitrogen fertilizer production and application was estimated with the help of the parameters given by domestic studies and IPCC. We further proposed that the available carbon sequestration potential of cropland soil could be taken as the criterion of the validity and availability of carbon sequestration measures. The results showed that the application of synthetic nitrogen fertilizer could bring about a carbon sequestration potential of 21.9 Tg C·a^-1 in current situation, and 30.2 Tg C·a^-1 with fertilization as recommended. However, under the two scenarios, the greenhouse gas leakage caused by fertilizer production and application would reach 72.9 Tg C·a^-1 and 91.4 Tg C·a^-1, and thus, the actual available carbon sequestration potential would be -51.0 Tg C·a^-1 and -61.1 Tg C·a^-1,respectively. The situation was even worse under the ‘fertilization as recommended’ scenario, because the increase in the amount of nitrogen fertilization would lead to 10.1 Tg C·a^-1 or more net greenhouse gas emission. All these results indicated that the application of synthetic nitrogen fertilizer could not be taken as a feasible measure for the carbon sequestration of cropland soil in China. Since synthetic fertilizer application is the basic guarantee of China’s crop production, it was suggested to increase the efficiency of synthetic nitrogen fertilizer, and at the same time, to cut down the synthetic nitrogen fertilizer production and its application on the premise that the crop yield should be ensured.

Key words: rhizosphere, Arachis hypogaea, drought and salt stress, bacterial community structure, 16S rRNA