Soil carbon sequestrations by nitrogen fertilizer application, straw return and no-tillage in China's cropland

Soil as the largest global carbon pool has played a great role in sequestering the atmospheric carbon dioxide (CO2). Although global carbon sequestration potentials have been assessed since the 1980s, few investigations have been made on soil carbon sequestration (SCS) in China's cropland. China is a developing country and has a long history of agricultural activities. Estimation of SCS potentials in China's cropland is very important for assessing the potential measures to prevent the atmospheric carbon rise and predicting the atmospheric CO2 concentration in future. After review of the available results of the field experiments in China, relationships between SCS and nitrogen fertilizer application, straw return and no-tillage (NT) practices were established for each of the four agricultural regions. According to the current agricultural practices and their future development, estimations were made on SCS by nitrogen fertilizer application, straw return and NT in China's cropland. In the current situation, nitrogen fertilizer application, straw return and zero tillage can sequester 5.96, 9.76 and 0.800 Tg C each year. Carbon sequestration potential will increase to 12.1 Tg C yr(-1) if nitrogen is fertilized on experts' recommendations. The carbon sequestration potentials of straw return and NT can reach 34.4 and 4.60 Tg C yr(-1) when these two techniques are further popularized. In these measures, straw return is the most promising one. Full popularization of straw return can reduce 5.3% of the CO2 emission from fossil fuel combustion in China in 1990, which meets the global mean CO2 reduction requested by the Kyoto Protocol (5.2%). In general, if more incentive policies can be elaborated and implemented, the SCS in China's cropland will be increased by about two times. So, popularization of the above-mentioned agricultural measures for carbon sequestration can be considered as an effective tool to prevent the rapid rise of the atmospheric CO2 in China.