Distribution characteristics of silicon, iron and aluminum in lime soil profile in karst mountainous areas: A case study of Qinglong county, Guizhou Province

The study site is located in Liancheng town, Qinglong county, Guizhou Province, an area with highly developed karst landforms dominated by mountainous lands. The area belongs to plateau subtropical monsoon climate with an average elevation of 1，442 m, annual precipitation of 1，500 to 1,650 mm, annual average temperature of 14 ℃, and frost-free period of about 320 d. The hilly area is dominated by limestone soils, with dominant vegetation species of fir and eucalyptus trees. This paper aims to understand the changes of silicon, iron and aluminum contents and the characteristics of weathering development through studying the limestone soil profile, which provide references for soil fertilization and associated improvement in the karst mountain areas. The mineral elements determination method (triacid digestion-atomic absorption spectrophotometry and aluminum reagent colorimetry and silicon-molybdenum blue colorimetry methods) and soil oxide determination method (sodium disulfite-sodium citrate-sodium bicarbonate method, acidic ammounium oxalate method and sodium pyrophosphate extraction-atomic absorption spectrophotometry ) were used to analyze the contents and variation characteristics of silicon, iron and aluminum elements. The results show that the content of silicon, iron and aluminum in karst mountain areas of Qinglong county is in the order of silicon>aluminum>iron, and the content of iron oxide is in the form of free state>amorphous state>complexation state. The conclusion is that the content of silicon, iron and aluminum in the soil profile of karst mountainous area in Qinglong county is higher, and mainly exists in the form of minerals. The constraints of soil formation factors and the environment resulting in low degree of desiliconization and iron aluminization in soil, slow accumulation of soil, lack of transition layers in soil profile and etc. all cause soil erosion and rocky desertification. Engineering and natural protection measures should be taken to prevent and control the vegetation cover reduction and ecological deterioration. Soil iron oxide is also an important indicator of weathering process, and the study of different forms of iron oxide can be conducted to understand the morphological and environmental behaviors of iron, which will assist in the study of soil development and soil environment in karst mountainous areas.