华北山地土壤CaCO_3含量/石灰反应垂直分布特征及其发生学解释

Vertical Distribution of Soil CaCO_3 Content/Lime Reaction in Mountainous Regions of North China and Its Genetic Explanation

为了探究华北山地土壤CaCO_3含量/石灰反应垂直分布特征及其发生学解释,对北京市、山西省257个山地土壤剖面的机械组成、CaCO_3含量和石灰反应进行统计分析。结果表明:华北山地表土的机械组成以粉砂为主,与黄土相似,说明黄土降尘是土壤矿物质的重要来源;海拔>1 500m的中山和高山地区的剖面,由于CaCO_3淋洗强,造成无论何种成土母质,CaCO_3被淋洗出土体,土壤通体无石灰反应;海拔介于500~1 500 m的中山地区和低山地区的剖面,CaCO_3淋洗弱,土壤普遍具有石灰反应,成土母质对土壤中CaCO_3含量/石灰反应起主导作用,生物气候条件的影响居于次要地位;海拔<500 m的低山丘陵地区的剖面,各土层的CaCO_3含量/石灰反应无明显分布规律。结论:黄土降尘为华北山地表土输入了碳酸钙,但由于不同海拔高度地区土壤湿度存在差异,导致土壤CaCO_3淋溶程度和含量差异明显。淋溶过程强弱导致的土壤CaCO_3含量/石灰反应垂直分布特征是华北山地土壤的典型发生学特征之一,不同海拔高度起主导作用的因素有所不同。研究成果可为华北山地土壤调查、发生与分类研究提供参考。

【Objective】Papers available in the literature show that loess dust precipitation exists generally in North China, becoming an important source of topsoil in the region. It brings in a large amount of fine mineral particles and nutrient elements, especially, CaCO3, to the soil. CaCO3 is an important component of the soils in arid, semi-arid and semi-humid regions, and hence a major indicator reflecting development degree of a soil. The purpose of this paper is to study vertical distribution of CaCO3 content and its characteristics in the mountainous soil of North China, in an attempt to explain causes of this phenomenon from the perspective of soil genesis. 【Method】A total of 257 soil profiles of various soil series in Beijing and Shanxi Province were investigated for mechanical composition, CaCO3 content and lime reaction and statistic analysis was performed of the data. On such a basis, vertical distributions of CaCO3 content and lime reaction in the mountainous soils of North China and their characteristics were summarized, and causes of the phenomena explained with the theory of soil genesis.【Result】Results show that the topsoil in North China is mainly composed of silt, which is similar to loess, indicating that loess dust precipitation is an important source of soil minerals, bringing in CaCO3 to the topsoils of the mountainous soils in North China. As soil humidity varies sharply from area to area due to difference in elevation, soil CaCO3 content does too. In areas above 1 500 meters in elevation, the soils are quite high in humidity（varying in the humid and damp regime） due to relatively high precipitation（mean annual precipitation of over 600 mm） and relatively low temperature（varying in the gelic or cryic soil temperature regime）, and good to vegetation, which in turn reduces surface runoff, but enhances downward leaching of CaCO3. As a result CaCO3 is leached out of the soil, no matter what it is derived from, and no lime reaction is detected throughout the solum. So in these areas, bio-climatic conditions play a leading role affecting soil CaCO3 content and lime reaction. However, in areas ranging between 500 and 1 500 meters in elevation, the soils are relatively low in soil humidity（varying in the semi-arid-humid/humid regime） due to relatively low precipitation（mean annual precipitation of 〈600 mm） and higher soil temperature（varying in the frigid/temperate regime）, and hence not so good to vegetation, As a result, CaCO3 leaching is weakened and lime reaction could be found almost everywhere. Therefore in these areas bio-climate conditions descend from the leading role to a major role, following behind the role of parent material. Whatever, no obvious characteristic of the distribution of soil CaCO3 content and lime reaction could be summarized in areas below 500 meters in elevation.【Conclusion】In conclusion, the characteristics of the vertical distribution of soil CaCO3 content/lime reaction caused by leaching process, strong or weak, is one of the typical soil genetic characteristics of the mountainous soils in North China.