Response relationships among CEC,mechanical compositions and mineral types in typical karst soil
In this study,a total of 146 profile samples were collected from 32 soil profile sampling sites in nine towns and cities in typical karst areas of Hunan Province. The physical and chemical properties of soil were analyzed through field investigation,excavation,and collection and description of soil profiles of limestone weathering parent materials. The relationships among soil CEC contents,mechanical compositions,and soil mineral types were also explored. The research findings laid a foundation for modification,fertilization and ecological restoration of karst soil.According to the Technical Specifications for Soil Analysis,the determination of soil physicochemical properties was conducted as follows:the soil pH values were measured by potentiometry. Both soil organic matters and total nitrogen contents in soil were determined by potassium dichromate heating method. Soil bulk density was measured by cutting ring method,while total phosphorus was assessed through the digestion-Mo-Sb anti-spectrophotometric method. Total potassium was analyzed via flame atomic absorption spectrophotometry. Exchangeable calcium and magnesium were quantified by EDTA titration method,and exchangeable sodium and potassium were also measued by flame atomic absorption spectrophotometry. The composition of soil particles was determined by pipette method,and the particle fraction was classified based on the system of United States (2.00-0.05 mm for sand,0.050-0.002 mm for silt,and<0.002 mm for clay). Types of clay minerals were determined by X-Ray diffraction. The cation exchange capacity (CEC) was determined by ammonium acetate centrifugal exchange method. The effective cation exchange capacity (ECEC) was calculated in the following formula:[cmol·kg-1]=H++Al3+(⅓Al3+)+total extractability base.The results shows as follows. (1) The CEC contents of typical karst soil in Hunan ranged between 2.71-13.9 cmol·kg-1,with an average value of 16.70±5.62 cmol·kg-1. The sample values exhibited considerable variability. The average soil ECEC was 8.86±3.75 cmol·kg-1,sigificantly lower than soil CEC. The particulate composition of soil was mainly silt and clay,resulting in a heavy texture and poor permeability in the study area. Based on the American grading method for soil fertilizer retention capacity combined with the measurement data,it was observed that the soil fertilizer retention capacity in the study area predominantly fell within the medium to strong levels,but the soil fertilizer capacity was inadequate. (2) The particulate compositions of soil followed a trend of clay>silt>sand,encompassing nine texture types. The soil samples with clay texture constituted the largest proportion of 31.50％. This was followed by silty loam and silty clay loam,which accounted for 30.14％ and 27.40％,respectively. The soil samples from the study area included five distinct mineral types:siliceous hybrid,illite hybrid,kaolinite,kaolinite hybrid and hybrid. The hybrid soil exhibited the highest sand content,while the siliceous hybrid had the highest content of powder silt,and the kaolinite hybrid contained the most clay. The CEC and ECEC contents were the highest in illite hybrid and lowest in hybrid soil. In general,the soil texture of the 146 samples was primarily clay,silty loam and silty clay loam,resulting in heavy and compact soil that adversely affected the air permeability and drainage of soil. (3) CEC exhibited a highly significant correlation with both silt and clay content,while showing no significant correlation with sand. Soil ECEC was not significantly correlated with any of the soil particles;however,it demonstrated a highly significant positive correlation with soil pH,organic matter content and total phosphorus content (P<0.01). Additionally,there was a significant positive correlation between ECEC and total potassium content,indicating a relationship between ECEC and the primary physicochemical properties of soil. This suggests that ECEC may influence the soil characteristics more effectively than CEC and could have a greater impact on soil fertility. (4) The primary exchangeable ions were Ca2+and Mg2+,with soil CEC showing an extremely significant positive correlation with K+,Ca2+,and Mg2+(P<0.01). Furthermore,soil ECEC was significantly positively correlated with K+,and extremely significantly positively correlated with Ca2+and Mg2+(P<0.01). Soil CEC was not correlated with mineral type,while ECEC was highly significantly negatively correlated with mineral type. The contents of Ca2+,Mg2+and K+in soil exchangeable salt-based ions also had an effect on the contents of CEC and ECEC in soils of different mineral types.In this study,soil CEC was found to be extremely significantly negatively correlated with silt contents. Conversely,there was a highly significant positive correlation with clay contents. This indicates that in karst soil,finer soil particles contribute to a more compact structure,which enhances soil cation exchange and improves soil fertilizer retention quality. However,the fertilizer environment can limit the nutrient cycle between soil and crops. By adjusting the proportions of silt and clay in soil,it is possible to increase the CEC value and enhance soil fertility. Although no significant correlation was observed between ECEC and soil particle compositions,ECEC was found to be significantly positively correlated with soil pH,soil organic matter contents,exchangeable Ca2+and exchangeable Mg2+. Additionally,it exhibited a highly significant negative correlation with soil mineral types,which better reflects the synergistic effects of soil fertility conservation and nutrient supply.
cation exchange capacitysoil particle compositionlimestone parent material
万方数据
维普
