滨海滩涂围垦对土壤团聚体分布及其有机碳富集的影响——以江苏省如东县垦区为例

The Impact of Reclamation on Soil Aggregates and Organic Carbon Enrichment in Coastal Areas: a Case Study in Rudong County, Jiangsu Province

有机碳是土壤质量的重要组成部分,团聚体在土壤有机碳固持方面扮演着重要的角色。海岸带土壤质量低下,随着滩涂围垦的不断深入,自然滩涂围堤挡水围垦后土壤的理化环境发生了明显的变化,由原先的还原环境向氧化环境转变,这一改变会直接影响土壤中团聚体及其有机碳的演变过程。本研究通过对江苏省如东县1951年和2007年围垦时期的垦区及自然滩涂的土壤样品采集,研究不同围垦时期滨海围垦对土壤有机碳含量、土壤团聚体及其有机碳分布的特征和变化过程。结果表明:研究区垦区表层土壤(0~20 cm)有机碳含量在0.2%~1.13%之间,均值为0.58%。亚表层土壤(20~40 cm)有机碳含量在0.22%~0.85%之间,均值为0.41%。从全国土壤有机碳的平均水平来看,研究区明显偏低。相比于围垦初期土壤有机碳(SOC)出现明显的下降,长期围垦可以显著增加土壤表层的SOC。滨海垦区土壤团聚体质量比从大到小分别为53~250μm、>250μm、<53μm团聚体。随着围垦时间的增加,>250μm和<53μm团聚体都呈明显的先减少后增加的趋势,53~250μm团聚体随着围垦时间的增加呈现先增加后减少的趋势。53~250μm团聚体土壤有机碳含量最低,其次为<53μm团聚体,而>250μm团聚体土壤有机碳含量最高。因此,围垦后广泛开展利于大团聚体形成的农业管理措施有利于围垦土壤质量的快速提升。

Soil organic carbon(SOC) is an important part of soil quality. Soil aggregates play an important role in SOC sequestration. Coastal soil quality is normally lower, since its physical-chemical properties undergo quick conversion from anaerobic to oxidative environment after growing reclamation of coastal zones, which lead to the significant changes the evolution of SOC and soil aggregates. This study selected two coastal reclamation zones(a long-term reclamation in Old Beikan from 1951 and a short-term reclamation in Yudong from 2007) and a reference natural saltmarsh to reveal the evolution of soil aggregates and SOC. The contents of SOC varied from 0.2% to 1.13%(mean value of 0.58%) in surface soil(0-20 cm) and from 0.22% to 0.85%(mean value of 0.41%) in subsurface soil(20-40 cm). Compared with the national average content of SOC, SOC in the study area was relatively lower. In the early time of reclamation(2007), SOC tended to be stable at soil depth of 0-40 cm, and decreased at soil depth of 20-40 cm. However, SOC increased significantly at soil layer of 0-40 cm after a longer-term reclamation(from 1951). The distribution of different size soil aggregates in the study area decreased in the following order: 53-250 μm, > 250μm, < 53 μm. The soil aggregate of > 250 μm and < 53 μm showed first decrease and then increase trend, while 53-250 μm aggregate showed opposite trend with reclamation years. SOC in 53-250 μm was lower than that in > 250μm and < 53 μm soil aggregate. The highest SOC was found in > 250 μm soil aggregate. Therefore, some tillage practices of promoting the large aggregation would be helpful for soil quality improvement.