The contribution of China's agricultural practice to atmospheric CO 2 has been paid a great attention because China has a long history of agriculture to support one-fifth of global population. Some authors have thought agricultural soils could sequester a considerable carbon to slow the rise of atmospheric CO 2. In fact, this sequestering potential depend on initial soil content, climate and cultivation. The long-term experiments in North America have proved that arable lands have been changing from a C s...