湖南典型农田土壤有机碳含量及其演变趋势

Change of Farmland Soil Organic Carbon Content in Typical Region in Hunan Province

以湖南省沅江市（28°42′～29°11′N、112°16′～112°56′E）为代表，通过典型样区密集取样分析和同一区域的历史资料比较，研究了洞庭湖区农业用地土壤有机碳的演变趋势，发现稻田土壤有机碳在最近25a中稳步增加，而改为旱地的土壤有机碳含量减少．2004年典型样区土壤有机碳均值为（26．66±4．93）g·kg^-1，主要分布区间为20～35g·kg^-1，比1979提高22．64％；其中耕作制度为双季稻的土壤有机碳含量，由1979年的20．29g·kg^-1提高到了2004年的28．12g·kg^-1，年均增加量约313．5mg·kg^-1（年递增率为1．15％）；耕作制度为一季稻的土壤有机碳含量，由1979年的20．29g·kg^-1提高到了2004年的27．25g·kg^-1，年均增加量约278．3mg·kg^-1（年递增率为1．16％），耕作制度为水旱轮作的土壤有机碳含量，由1979年的20．29g·kg^-1提高到了2004年的23．90g·kg^-1，年均增加量约144．5mg·kg^-1（年递增率为0．78％），而改为旱地的土壤有机碳含量，由1979年的20．29g·kg^-1降低到了2004年的18．40g·kg^-1，年均减少量约75．48mg·kg^-1（年递减率为0．37％）．方差分析表明，稻田土壤有机碳的增加达到了极显著水平，改为旱地的土壤有机碳含量的减少未达到了显著水平．表明洞庭湖区不同利用类型的土地均是重要的固碳场所，农业用地的土壤有机碳库是大气CO2循环的“汇”，而不是“源”．

Taking Yuanjiang City（ 112° 16′ - 112°56′E ,28°42′- 29° 11′ N） in Hunan Province as an example, the changes of soil organic carbon content and its distribution in farmland soils in Dongting Lake region were investigated, based on the dense sampling in typical plots and the investigation of historical materials. The results showed that soil organic carbon in different land uses and cropping systems,such as rice/rice, rice,paddy-upland rotation, increased stably, but soil organic carbon in dry land induced in some extent. Mean soil organic carbon content in farmland soils of the typical sampling region in 2004 was （26.66 ± 4.93 ）g· kg^- 1. Compared with that in 1979,soil organic carbon content increased by 22.64 %. In 1979, soil organic carbon content in paddy soil mainly ranged from 20g· kg^- 1 to 25g· kg^- 1 （frequency is 62.5 % in all sampling plots）, and in 2004 increased to 20 - 35g· kg^- 1 （ frequency is 88.0 % ）. This indicated that soils under different types of land use in Dongting Lake region could all store carbon, and organic carbon pool in farmland soils would play ＂sink＂ role in the cycle of atmosphere CO2.