横断山区干旱河谷小流域土壤特性的空间分异

Spatial Differentiation of Soil Properties in the Dry Valley along a River's Length of the Hengduan Mountains

研究土壤质量的空间异质性在深入了解区域土壤质量分布规律以及促进生态系统可持续发展方面具有重要的意义。对金沙江小支流黑水河干热河谷上游、中游和下游三个断面不同海拔土壤性质的垂直变化规律进行了深入系统地研究。结果表明,在整个流域干热河谷土壤有机质垂直方向上变化幅度较小,上游马桑坪垂直断面碱解氮和有效磷在海拔1 400 m和1 740 m含量最高;中游披砂断面碱解氮和有效磷在1 100~1 200 m的河谷地带高于海拔较高地带的土壤,同时随着海拔上升含量逐渐降低;下游的葫芦口垂直断面碱解氮和有效磷在海拔700 m左右退化最为严重。在交换性能方面,马桑坪断面土壤交换性钙和镁以及交换性盐基总量在海拔1 400 m处高于其上或者其下地带;交换性钾变化比较小,以河谷地带最低;中游披砂断面土壤交换性阳离子和交换性盐基离子总量均随海拔增加而降低,而在海拔2 000 m又有所增加;葫芦口土壤交换性能垂直变化方面,交换性钙、镁和钠,以及盐基总量随着海拔高度的增加而降低,交换性钾变化趋势则相反,随着海拔的升高而增加。这些结果表明,即使在同一干旱河谷,在不同地段由于环境条件不同,在垂直方向上土壤质量不同指标变化程度不同,在土壤质量评价与退化防治中应有所区别。

Typical dry valley of Jinsha River is characterized by dry season and monsoon,which is very susceptible to soil degradation in the context of the fragile environment.In order to assess the impacts of environmental gradients on soil chemical fertility quality of dry valleys,soil chemical fertility status in dry valley of Heishui River,one branch of Jinsha River,have been monitored.The results showed that soil chemical properties were impacted significantly along altitudinal gradients.There was no difference in contents of soil organic matter of all elevations.Available nitrogen and available phosphorus along Masangping（upstream） altitudinal gradients were the highest from 1 100～1 200 m asl;while along Pisha（midstream） altitudinal gradients they were the highest from 1 100～1 200 m asl,and would decrease with elevation.Available nitrogen and available phosphorus along Hulukou（downstream） altitudinal gradients deteriorated greatest from about 700 m asl.Soil exchangeable Ca,Mg and base along Masangping altitudinal gradients were the highest at 1 400 m asl,and exchangeable K was the lowest in riverbank.Soil exchangeable cation and base decreased along Ningnan altitudinal gradients with elevation while increased above 2 000 m asl.Soil exchangeable Ca,Mg,Na and base along Hulukou altitudinal gradients decreased with elevation while soil exchangeable K increased with elevation.Therefore,assessment indices of soil quality and countermeasures of degraded soil restoration should be adapted even in a dry valley because dominant factors reflecting changes in soil quality vary with different section from upstream to downstream.