江西兴国水土流失治理区土壤有机质动态变化

Dynamic analysis of soil organic matter contents in soil and water conservation region of Xingguo County, Jiangxi Province

在ArcGIS8.1软件系统平台上,用普通克立格和概率克立格等多种方法研究潋水河流域土壤有机质含量的动态变化特征。结果表明,潋水河流域106个样点的土壤有机质平均含量增加,由1981年的18.16±7.23g/kg增加到2002年的19.14±11.25g/kg;2002年土壤有机质含量为(30.0～40.0g/kg)、(20.0～30.0g/kg)级地的面积扩大,所占流域面积比分别较1981年增加11.38%和28.54%。近20年来该流域内水田、旱地和林地的土壤有机质平均增加量分别为2.3g/kg、3.5g/kg和3.1g/kg,坡度≤2°、2～6°、6～15°、15～25°和>25°的土壤有机质平均增加量分别为1.8g/kg、2.6g/kg、3.3g/kg、3.6g/kg和4.0g/kg。结合概率克立格法和加权平均法探讨了<10.0g/kg含量水平下区域土壤有机质的概率分布特征,其几何平均概率由1981年的0.2008下降到2002年的0.1503。

Soil organic matter (SOM) is of primary importance for maintaining soil productivity, and an important indicator of soil quality. It helps to prevent erosion and desertification and is a driving variable in environment changes since it acts as the source and sink of carbon dioxide. In this paper, the temporal-spatial variability of SOM contents was analyzed in the Lianshui Basin (Xingguo County, Jiangxi Province, China) over an area of 579km2 from 1981a to 2002a. It not only can help us to understand the dynamics of SOM during soil and water conservation, but also provide a theoretical basis of soil and water conservation, ecosystem restoration and ecosystem rebuilding for southern hill region in China. The SOM contents in 1981 came from the map of SOM contents in the second national soil survey. According to the natural environment and social economy differences, the sampling point scheme in 2002 was devised by combining grid sampling points with a hierarchical sampling method. 106 spots were sampled and their positions were located by GPS (Global Position System). The topsoil samples of three random sites in the same field (0~30cm) were mixed together for the chemical analysis. The SOM contents in 2002 were analyzed by the Walkley-Black wet combustion while the SOM contents in 1981 were looked up in the map of SOM contents in 1981 which was provided by agricultural bureau of Xingguo County. Spatial analyses were performed by the software ArcGIS8.1 such as semivariance, ordinary kriging (OK) and probability kriging (PK). Conventional analytical results indicated that the topsoil organic matter content was 19.14±11.25g/kg in 2002, comparing to 18.16±7.23g/kg in 1981. The coefficient of variation changed from 39.4% in 1981 to 58.8% in 2002, which was attributed to the changes in managements such as the quality and quantity of applied manure. The results indicated that the spatial random variability of SOM contents became more apparent after 21 years. Trend distribution maps of SOM contents by geostatistics of ArcGIS reflected the golden trend of SOM contents on the east-west and north-south. The results showed that SOM contents on the east-west and north-south both approximately presented linear and increased gradually from southwest to northeast in 1981; SOM contents in 2002 almost presented parabola, the southwest and northeast were both higher than the center. The results indicated that SOM contents in the southwest and northeast increased generally while the center kept constant. The ratio of nugget to sill of SOM spatial variability in the topsoil in 1981 was 0.22, indicating that the random variability was small or structural variability was apparent. But the range is only 1.55km in 1981. However, the percentage of random variability in the spatial variability of SOM got to 0.74, and the range increased to 6.23km in 2002. It showed that land managements had obviously impacted on the spatial heterogeneity degree of SOM during the closing hillsides to facilitate afforestation and forest rehabilitation in the basin. Spatial analyses that were through overlapping the grid layers of two ages indicated that SOM contents of local regions varied greatly in the Lianshui Basin. SOM contents of 74.8% of the basin area increased and the other decreased. After the application of closing hillsides to facilitate afforestation in the recent 20 years, the woodland became dense, and the accumulation of SOM contents increased apparently. At the same time, the application of forest rehabilitation in part steep slopland resulted in the reduction of dry land and the expansion of woodland, forest coverage rose. Hence, SOM contents of 74.8% of the basin area increased which were mainly distributed in the west and along the north border of the basin. By contrast, SOM contents in 25.2% of the basin area decreased which stretched from the south outskirt of Gulonggang Town to the groove of Gulonggang syncline due to the distribution of granite that resulted in the sparse vegetation and soil and water loss. Based on the accessing criteria of