宁夏盐池县沙化草地土壤团聚体分异特征

以宁夏盐池县哈巴湖自然保护区不同沙化程度的荒漠草原为对象,研究潜在、轻度、中度和重度沙化草地0~40 cm土壤机械稳定性和水稳定性团聚体的粒径分布,并通过团聚体破坏率、平均重量直径(MWD)、几何平均直径(GMD)和分形维数等指标分析不同沙化类型草地土壤团聚体稳定性特征。结果表明:各沙化类型草地0~20 cm土层机械稳定性团聚体和0~40 cm土层水稳性团聚体均以<0.25 mm微团聚体为主,分布范围分别为45.78%~88.36%和48.05%~97.79%。随草地沙化程度的加重,0~40 cm各土层<0.25 mm机械稳定性和水稳性微团聚体含量、团聚体破坏率、分形维数及侵蚀因子总体呈增加的趋势,MWD和GMD则逐渐降低,土壤结构趋于不稳定。从剖面变化看,随土层的加深,土壤稳定性增加,尤其是潜在和轻度沙化草地,表明该区域土地沙化主要发生在0~20 cm浅层土壤。土壤团聚体稳定性与有机碳、全氮含量呈极显著正相关(P<0.01),与黏粉粒呈显著正相关(P<0.05),与土壤容重呈极显著负相关(P<0.01)。伴随着盐池县草地沙化过程中土壤细颗粒的吹蚀和碳氮等养分的搬运,土壤结构分散,物理稳定性降低。

Size distribution of soil aggregates in different grassland desertification categories in Yanchi County,Ningxia

This study evaluated the particle size distributions of mechanically stable and water stable aggregates in the 0-40 cm soil depth in different categories of desert steppe grassland in the Haba Lake Nature Reserve in Yanchi County, Ningxia. Potentially desertified grassland, lightly desertified grassland, moderately desertified grassland and severely desertified grassland were studied. The stability characteristics of soil aggregates were evaluated using aggregate destruction rate (PAD), mean weight diameter (MWD), geometric mean diameter (GMD), fractal dimension and soil erosion factor data. It was found that the mechanically stable aggregates in the 0-20 cm soil layer and the water stable aggregates in the 0-40 cm soil depth of each grassland desertification category were dominated by <0.25 mm micro-aggregates with the percentage of these being 45.78%-88.36% and 48.05%-97.79% respectively. The <0.25 mm mechanically stable and water stable micro-aggregate contents, PAD, fractal dimension and erosion factor in the 0-40 cm soil depth all increased with increasing grassland desertification, while the MWD and GMD gradually decreased, and the soil structure was variable. The soil stability increased with depth in the soil profile, especially in the potentially and lightly desertified grassland, which indicated that the land desertification in this grassland mainly occurs in the upper 20 cm of the soil profile. The stability of soil aggregates was positively correlated with organic carbon content, total nitrogen content (P<0.01), and silt and clay particles (P<0.05), and negatively correlated with soil bulk density (P<0.01). With the erosion of fine soil particles and transportation of nutrients such as carbon and nitrogen in the process of grassland desertification in Yanchi County, soil structure and physical stability is reduced.