近20年来宜兴市域水稻土有机碳动态及其驱动因素

中国农业土壤有机碳的变化一直是国内外农业与全球气候变化研究中十分注意的问题。一些研究提示20世纪末以来我国水稻土尤其是太湖地区水稻土的有机碳储存出现了增长趋势。文章选择了2002年对江苏省宜兴市市域范围水稻土的61个土壤监测点进行系统采样和土壤分析,并与该市分别于1983年和1994年进行的土壤肥力调查结果相对比,从县市区域尺度分析、评价了近20年来太湖地区水稻土表土有机碳储存的变化。尽管20世纪80年代初以前土壤有机碳含量变化以下降为主,但20年来该市域内水稻土有机碳总体上呈上升趋势。统计表明,4个主要土属的表土有机碳密度的增幅以下序递增:湖白土(-2.80tChm2)2)2)2),因而全市74.2×103hm2水稻土表土的总有机碳库从1983年的1.37Tg增加到2002年的2.20Tg。该市水稻土的平均固碳速率达到0.5～0.8tChm2a,这种快速固碳作用与20世纪80年代以来土壤中氮素的富集、秸秆还田的推广和90年代以来该地区不断扩大的冬季休闲有关。目前该市水稻土的固碳潜力仍很大,太湖地区的高产高投入农业不能排除在碳固定上的积极意义。然而,这种快速固碳作用的土壤过程和机理值

DYNAMICS OF TOPSOIL ORGANIC CARBON OF PADDY SOILS AT YIXING OVER THE LAST 20 YEARS AND THE DRIVING FACTORS

Understanding baseline C pools and the recent change at regional scale is fundermental for approaching C sequestration agriculture with BMP practices in China. In this study, 61 sites within the framework of soil monitoring system of Yixing Municipality, a region of different paddy soils, were sampled depth at 0～5cm and 5～15cm respectively. SOC determination was carried out for all the samples. The sample number of each kind of paddy soils depends on the dominance in the area. The SOC data were compared with those collected respectively in 1983 and 1994 in same locations. It is clear that there has been prominent trend of SOC increase for the last 20 years although the degree of SOC increase varied with the species and agricultural practices. The rise of SOC density ranges from -2.80tC/hm ² of Hubaitu, a bleached soil to 14.97 tC/hm ² of Huangmitu, a Fe accumulated soil rich in SOC. It means that total baseline topsoil SOC pool is raised from 1.37Tg in 1983 to 2.20Tg in 2002 at an area of 74.2×10 ³hm ². The increase of SOC was found related to the clay (<0.002mm) content and N enrichment in soils. It means that paddy soil with high clay and N enrichment is favorable for SOC accumulation in these paddy soils. The high C sequestration rate found in these paddy soils could be attributed to agricultural practices such as residue re entering and manure application, shifting rice wheat rotation to rice fallow and rice rape seed rotation. The authors believe that the high input and higher yielding may not be negative to the enhanced topsoil SOC storage.