岩溶山地土壤氧化铁形态及其与成土环境的关系

土壤氧化铁的数量和形态是成土过程和成土环境的反映.以重庆金佛山为研究对象,采用化学选择溶解法,分析了岩溶山地土壤铁氧化物数量与形态,并探讨了氧化铁数量、形态与成土环境、岩溶环境退化和石漠化发生发展的关系.结果表明,山顶区与坡腰区全铁含量差异大,山顶土壤全铁51.49 g.kg-1,坡腰区全铁含量86.29 g.kg-1,土壤全铁主要受母质影响.山顶区气温低,土壤发育程度弱,黏粒游离铁含量低（29.16 g.kg-1）,黏粒部分铁的游离度小（35.40%）;坡腰区气温高,土壤风化程度较深,黏粒游离铁含量高（43.92 g.kg-1）,黏粒铁的游离度高（60.41%）.山顶区低温潮湿,土壤有机质含量高,铁的活化度和络合度高（73.51%和17.21%）,显著高于坡腰区（13.06%和0.41%）.在坡腰区,灌丛马尾松退化或转化为旱地后,土壤有机质含量下降,黏粒流失,游离铁有伴随黏粒迁移的趋势,使土壤全铁和黏粒游离铁减少;灌丛马尾松土壤全铁98.25g.kg-1,坡耕地84.52 g.kg-1;灌丛马尾松黏粒游离铁50.81 g.kg-1,坡耕地47.86 g.kg-1.土壤铁氧化物数量与形态可以表征岩溶环境退化及石漠化发生发展状况.

Morphology of Soil Iron Oxides and Its Correlation with Soil-Forming Process and Forming Conditions in a Karst Mountain

The quantity and morphology of iron oxides are indicators of soil forming-process and forming conditions. In order to analyze the connection between soil iron oxides and soil forming conditions and degenerative process of karst ecosystem, we have chosen 14 soil profiles on the top and middle section of Jinfo Mountain, a typical karst slope in Chongqing, China. Morphology and contents of soil iron oxides were studied by using chemical selective extraction techniques. We draw conclusions: 1 total iron (Fe_t) is mainly controlled by parent material and lithology. Significant difference of Fe_t content exists between soils in Top Mountain (51.49 g·kg^-1, mean value from 5 profiles) and soils at the middle sector of North Slope (86.29 g·kg^-1, mean value of 9 profiles); 2 the results show low concentration of Fe_d (29.16 g·kg^-1) and low ratio of Fe_d to Fe_t (35.40%) in soil clay under conditions of high elevation and low temperature on Top Mountain. In contrast, the results indicate advanced weathering and soil-forming process at middle slope sites due to high temperature; this is supported by high mean values of Fe_d (43.92 g·kg^-1) and ratio of Fe_d/Fe_t in clay (60.41%); 3 long humid climatic setting and large numbers of soil organic matter on top of the mountain result in high activation degrees (Fe_o/Fe_d) and high complexation degrees (Fe_p/Fe_d); mean values of them are 73.51%, 17.21% respectively, which are higher than that of soils at middle slope sites (13.06%, 0.41%); 4 after degradation or deforestation of secondary forestland (pinus massoniana among bushes) at middle section of the hillslope, soil free iron oxides (Fe_d) and total iron oxides (Fe_t) decrease as well as soil organic carbon and clay, because of progressively increasing of soil erosion. Average contents of Fe_t and Fe_d in clay from 2 shrub profiles are 98.25 g·kg^-1, 50.81 g·kg^-1 respectively. However, the four tillage soils we have studied reveal lower values of Fe_t (84.52 g·kg^-1) and Fe_d in clay (47.86 g·kg^-1). Soil iron oxides are reliable indicators to estimate degeneration of karst ecosystem and karst rock desertification.