喀斯特山区不同草地土壤结构及分形特征

以喀斯特区域不同草地生态恢复阶段为研究对象,采用时空互代法对喀斯特山区耕地、退耕还草地、草地、林草间作地的土壤颗粒、团聚体、微团聚体粒径分布及分形维数进行研究,并分析分形维数与土壤理化性质的相互关系。结果表明,在石漠化恢复过程中,粗粒径微团聚体、团聚体含量随生态的不断恢复而增加,细粒径含量降低,但土壤机械组成与之相反。0~10 cm土层土壤微团聚体平均重量直径(MWD)表现为林草间作地、草地>耕地>退耕还草地,退耕还草地显著低于其他草地类型,分别比林草间作地、草地、耕地低0.15、0.15和0.11 mm;团聚状况在10~20 cm下均表现为草地>林草间作地>耕地>退耕还草地,其中退耕还草地显著低于林草间作地和草地,分别低8.26%和13.18%;土壤结构特征表明退耕还草地结构最弱。生态恢复过程中,土壤微团聚体和团聚体的分形维数从大到小依次为退耕还草地>耕地>林草间作地>草地,土壤颗粒分形维数从大到小依次为草地>林草间作地>耕地>退耕还草地,表明喀斯特山区土壤结构随生态恢复而逐渐变好,土壤分形维数一定程度上能反映喀斯特石漠化区域生态恢复的过程与特征。同时喀斯特地区土壤分形维数与其理化性质存在较好的相关性,微团聚体及团聚体分形维数能够较好的表征土壤结构及抗蚀能力的强弱。在石漠化区域生态恢复与石漠化治理过程中,通过人工调控措施,缩短退耕还草阶段,加快草地等植被覆盖度的增加,能有效减少水土流失,改善该区生态环境。

Soil structure and fractal characteristics of different land categories in a karst rocky desertification area

This research studied soil properties in different stages of grassland ecological restoration in a karst area. Specifically, the size distribution of soil particles, and the fractal dimension of soil aggregates and micro-aggregates were evaluated for farm cropland (FC), land in conversion from cropland to grassland (CCG), grassland (G), and forest and grass intercropped land (FGI), in a karst mountainous. These four spatially separated land categories were considered to represent a land restoration time series. Results were obtained from a combination of field sampling and laboratory analysis, and the relationship between fractal dimension of soil aggregates and soil physical and chemical properties was also analyzed. It was found that during the process of ‘rocky desertification restoration', the proportion of larger-diameter micro-aggregates and aggregates increased across the ecological restoration time series, while the proportion of smaller-diameter soil peds decreased. However, the mechanical composition of soil showed an opposite trend. The mean weight diameter (MWD) ranking of soil micro-aggregates in 0-10 cm soil layer was: FGI=G>FC>CCG. Quantitatively, the MWD of soil micro-aggregates in CCG was 0.15, 0.15 and 0.11 lower than other grassland types, which was 0.15, 0.15 and 0.11 lower (P<0.05), respectively, than that of FGI, G, and FC land. Soil micro-aggregate MWD in 10-20 cm soil layer ranked G>FGI>FC>CCG, and values for CCG were 8.26% and 13.18% lower (P<0.05), respectively, than those for FGI and G. The soil structure characteristics were weakest in CGC land. Across the ecological restoration time series, the fractal dimensions of soil micro-aggregates and aggregates ranked in descending order: CCG>FC>FGI>G, while the fractal dimensions of soil particles ranked in descending order: G>FGI>FC>CCG. These results indicate that soil structure in this karst mountain area is gradually improved with ecological restoration, and the soil fractal dimensions reflect soil restoration status in the karst rocky desertification area to some extent. At the same time, the fractal dimension of these soils correlates well with their physical and chemical properties. The fractal dimension of micro-aggregates and aggregates can better represent the strength of soil structure and erosion-resistance. In the process of ecological restoration and control of rocky desertification, human input that shortens the time needed to return farmland to grassland or accelerates increase of vegetation coverage, can effectively reduce soil erosion and improve the ecological environment of the region.