海南岛北部玄武岩上土壤发生的化学特性研究

A STUDY ON THE CHEMICAL PROPERTIES OF THE SOILS DERIVED FROM BASALT IN NORTHERN HAINAN ISLAND

海南岛北部不同时期喷发的玄武岩上发育的土壤构成一个风化成土时间系列。对这一土壤系列的化学特性研究表明 ,随风化成土时间的增加 ,pH值不断下降 ,但至富铁土后 ,pH趋于稳定 ,而土壤CEC7,盐基饱和度下降。同时 ,土体中Al2 O3 、Fe2 O3 、TiO2 含量增加 ,而Ca、Mg、K、Na淋失强烈 ,SiO2 含量也不断降低。以土壤中大量元素含量为基础计算多数指标难以反映热带地区碱金属和碱土金属元素迅速而强烈淋失的成土风化过程。常用的土体分子硅铝率和硅铁铝率并不能指示所有土壤的风化成土作用程度。

The soils, developed from basalts erupted in different periods of Quaternary, consititute a chronosequence of soils formation in northern Hainan Island. The study on chemical features of the soils showed that with the age of soil formation increasing, pH values decreased till Ferrosols formed, and then it almost unaltered, while CEC 7, SUM of bases, and base saturation degree declined with increase of soil age. However, the contents of Al 2O 3?Fe 2O 3?TiO 2 increased in fine earth fraction of soils, and Ca, Mg, K, Na leached out of soils extensively and rapidly with reduction of SiO 2. Such indices as CIA, CIW, A, B, β,ba, etc., depending on the contents of major elements in soils, could not illustrate the degree of soil weathering at development stage of soils, in which alkaline and alkaline earth elements leaching extensively in tropical region, but might evaluate the extent of leaching and weathering at early stage of rock weathering and soil formation, e g. Entisols. Implication of the silica alumina molecular ratio and silica sesquioxide molecular ratio of fine earth fraction in soils on soil weathering was weak at early stage of soil development (Entisosl, Cambisols, etc.), but could infer soil weathering degree and relative soil ages in moderate and high ferrallitic soils (Ferrisols, Ferralisols).