广西(山弄)岗自然保护区石灰土的地球化学特征

我国碳酸盐岩分布很广,占全国土地总面积的七分之一,而以广西、贵州和云南最为集中^1]。在热带、亚热带地区,由其风化发育的土壤与赤红壤、红壤显著不同,通称为石灰土,归于隐域土中。

THE GEOCHEMICAL CHARACTERISTICS OF LIMESTONE SOILS IN LONGGANG AREA, GUANGXI

Longgang Natural Reseave Area is one of the typical karst area under evergreen monsoon forest nearby the north margin of the tropics in China. Studies on chemical composition of soils, rocks, plants and ground water have showed that the main soul type is brown rendzina in this area. During the process of soil formation, the loss rate of elements by leaching is more than 70%. The trauslocation sequence of the elements by leaching is as follows: Ca>Mg>IC>P>Al>Mn>Fe>Si The calcium content of the soils derived from the rocks rich in Ca up to 50% (CaO) may decrease to 1-5% in the process of soil formation. However, calcium is still the most important element in biogeochemical environment of limestone soils. A great deal o,f calcicolous plants have grown in this area, which then brings about the accumulation of calcium to some extent in soils. The sequence of elements absorbed by plant is as follows: Ca>K>Na>P>Mg>Si>AL>Fe, while the sequence of element recovery is as below: N>Ca>Na>K>Mg>P>Si>Fe>Al. According to the data calculated from corrosion rate of limestone, specific gravity of calcite, amount of elements eluviated and illuviate.d and soil b ulk density, it is estimated that to form a solum with a thickness of 1 cm needs about 13,000-32,000 years. Because the li-mestone soils are usually characterized by the higher fertility and thin and erodible aolum, vigorous biological cycling of materials and rich biological resources. The eco-system in the region of this soil is fragile, once the system is destroyed, it is difficult to recover. It is suggested that in utilization of the soils, account should be taken into the conservation of the natures resources, which includes plantation of special economic forests.