成都经济区浅层土壤地球化学特征的土壤分类学意义

Soil geochemical characteristics from Chengdu Economic Zone and implications for soil classification

土壤的科学分类是土壤资源开发和利用的基础,土壤的系统分类以定量化、标准化和国际化为特点,但其大众化水平有待进一步提高,尚需加强与土壤发生分类的参比研究,并深化其在农业生产应用、土壤环境评价等方面的实践意义。自上世纪末至今,在我国东部开展了大面积、高密度的以土壤为主要介质的多目标(如农业和环境等)地球化学调查,获得了海量的地球化学数据,这无疑也为土壤分类指标化提供了全新资料。利用四川省成都经济区多目标地球化学调查获得的3061个浅层土壤样品(0～20cm)的52个元素全量和pH值分析数据,按照已知的土壤发生分类类数(8种土类)进行了样品聚类分析。结果表明:(1)浅层土壤的地球化学数据能较好地用来区分两类土壤,即紫色土一类的幼年土壤(在很大程度上继承了母岩、母质的地球化学特征)和受强烈人为活动水耕、旱耕熟化的土壤(外来物质的不断加入显著地改变了浅层土壤原有的地球化学性质);(2)各类土壤因母岩母质和利用方式不同,各具明显的标志性元素组合特征,如紫色土(高Ca和pH值)、黄壤(低碱和碱土金属元素和pH值)、水稻土(高有机元素、肥料元素和重金属元素)和潮土(高造岩副矿物元素)等,因此,这些元素组合是土壤分类两个要素(母质和人为作用)的重要参照系;(3)浅层土壤的地球化学特征不可能完整地体现成土条件、成土过程和土壤属性这三个发生分类依据,因此,聚类分析结果与发生类型之间存在一定的差异。

Scientific classification of soils is the basis of utilization and exploitation of soil resources. However, Soil Taxology, characterized by quantification, standardization and internationalization, is not popularized by far. So it is necessary to study its relationship with soil genesic classification and its application for agriculture and environment. From the end of the last century, Multi-target Geochemistry Survey （MGS） on soils aiming at agriculture and environment etc. has been launched in eastern China. Vast geochemical data of soils obtained through MGS may also provide bran-new clues to soil classification indexes. In this paper, data of 3061 surface （0-20 cm） soil samples containing 52 elements total contents and pH values obtained from Chengdu Economic Zone, Sichuan Province, are analyzed by cluster analysis, the numbers of which are equal to the group ones of soil genesic classification. It is concluded that, first, geochemical data of the surface soils can clearly distinguish two kind of soils, that is, juvenile soils, for example, purple soils, which inherits most geochemical characteristics of the parent rocks or materials, and anthropic soils, the geochemical characteristics of which have been greatly changed as the results of intensive impact from variety of agricultural uses （stagnic and orthic）. Second, different soils have typical indicator elements association respectively due to different parent rocks or materials and utilization, such as purple soils （high Ca content and pH value）, yellow soils （low alkali and alkaline-earth metal contents and pH value）, paddy soils （high organic element and heavy metal elements contents） and fluvo-aquic soils （high rock- forming accessory mineral elements contents） and so on. Consequently, it can be suggested that elements association is an important indicator for two key factors （parent materials and anthropic activities） of soil classification. Third, some differences exist between soil genesic classification and result of cluster analysis, because geochemical characteristics of surface soils can not completely represent the foundation applying to soil genesic classification, that is, condition and process of soil-forming, and soil property.