Estimate of carbon sequestration under cropland management in China

中国人. 长期大规模翻耕和秸秆燃烧造成土壤有机质（SOM）大量损失，使农田成为温室气体的一个排放源。然而，近年来，随着免耕技术的逐步推广、秸秆还田面积的增加，加上施肥、灌溉等农田管理措施的应用，农田土壤有机碳（SOC）储量有所回升，预计其将成为温室气体的吸收汇。本文通过分析各种农田管理措施下土壤有机碳（SOC）的变化量，估算中国农田管理土壤碳汇量，为制定中国农田温室气体清单提供科学参考。通过查阅相关文献著作等，构建农田管理情景，分析各管理措施长期定位试验土壤有机碳变化量的数据。根据中国农作制的分区，估算各区域及水田、旱地农田管理下的碳汇量，并与政府间气候变化专门委员会（IPCC）制定的2006IPCC国家温室气体排放清单指南中农田仍为农田的层次（Tier）2方法的估算结果进行比较。最后用Meta分析法估算中国农田管理土壤碳汇量。不同农田管理措施对土壤碳的影响不同。各种措施表现为化肥与有机肥配施的增碳作用最大，达到0.889 tC•ha-1•a-1；其次为秸秆还田、施有机肥和免耕，分别为0.597、0.545、0.514 tC•ha-1•a-1；施化肥的作用最不明显，仅为0.129 tC•ha-1•a-1。这一结果明显高于IPCC Tier2方法估算的结果。研究还揭示，不同管理措施在不同区域对土壤有机碳变化的影响存在一定的差异，黄淮海区、长江上中游区和西南区增加量较大，东北区增加量较小，在施化肥条件下东北黑土SOC甚至有降低的趋势。土壤有机碳的年增长率和初始值之间呈很好的负相关，由此可得出不同管理措施下农田土壤有机碳的平衡值及固碳潜力。农田管理措施中，配施、秸秆还田、施有机肥和免耕可以在很大程度上提高土壤SOC含量。其中，配施和秸秆还田的固碳潜力较大。

英语. Long-time conventional tillage on a large scale and straw burning cause significant losses of soil organic matter (SOM); this makes cropland an emission source of greenhouse gas (GHG). However, in recent years, organic carbon in cropland has been increasing due to the spread of no-tillage techniques, and increas of straw returning area, as well as extensively cropland management such as fertilization and irrigation. This can turn the cropland into an important sink of GHG. This paper analyzed the change of soil organic carbon (SOC) under different cropland management regimes, estimated carbon sequestration under cropland management in China. The results will be the base for a GHG inventory of Chinese croplands. Through reviewing relevant references and constructing cropland management scenarios, the change of SOC under different cropland management regimes in long-term experiments were analyzed. In addition, according to farming system regions in China, the quantities of carbon sink under cropland management regimes were estimated and compared with the results of Tier2 approach of cropland remaining cropland in 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Finally, Meta-Analysis was used to estimate carbon sequestration under cropland management regimes in China. The most successful management system for increasing SOC was using inorganic and organic fertilizers together, which could increase SOC 0.889 tC•ha-1•a-1. Next came straw returning, using organic fertilizer and no-tillage, respectively achieving 0.597, 0.545, 0.514 tC•ha-1•a-1. The effect of using inorganic fertilizer was not evident, only reaching 0.129 tC•ha-1•a-1. On the whole, these values were significantly larger than those of Tier2. Results also showed the change of SOC varied with different management systems and different areas. The increase of SOC in the Yellow-Huaihe-Haihe Rivers region, the upper and middle reaches of Yangtze River region and the southwest region was higher than that in the northeast region. There was even a decrease in SOC in Black Soil organic in the Northeast under application of inorganic fertilizer regimes. There was a negative relation between the annual growth rate of SOC and the value under cropland management. So the balance of SOC and carbon sequestration potentials could be estimated under different management systems. The cropland management techniques of using inorganic and organic fertilizer together, straw returning, using organic fertilizer and no-tillage could all increase SOC significantly. Carbon sequestrations of straw returning and using inorganic and organic fertilizer together were great.