Correlations Between Soil Cd Content And Soil Physical-chemical Properties Of Typical Paddy Soils In Hunan Province

In the paddy soil ecosystem of Hunan Province,the sources of soi cadmium(Cd)are complex and unclear.In this study,we selected typical paddy soils in five regions of Hunan Province.The five regions are central Hunan(Yiyang,Loudi,Shaoyang cities),southern Hunan(Hengyang,Chenzhou,Yongzhou cities),Northern Hunan(Changde,Yueyang cities),Western Hunan(Xiangxi,Zhangjiajie,Huaihua cities),eastern Hunan(Changsha,Zhuzhou,Xiangtan cities).The representative paddy soils developed from different parent materials were selected in each region.Soil profile samples were collected during the winter fallow period of double cropping rice field from November 2014 to March 2017.Through field investigation,paddy soil sampling sites of typical parent material were determined,and soil profiles(generally 0-140 cm deep)were excavated(the total number of soil profiles was 62).According to the principle of soil taxonomy classification in China,the genetic horizons in soil profiles were divided.The total Cd and available Cd content,p H value,soil organic matter,free iron oxide and soil particles(sand,silt and clay)were analyzed.This study aimed at understanding the Cd content and distribution characteristics of paddy soils from different parent materials,soil types and soil layers,analyzing the relationships between soil Cd content and soil physical and chemical properties,and exploring the main influencing factors of Cd content in typical paddy soils.The main results are as follows:(1)Among the six paddy soils developed from diffferetn parent materials in Hunan Province,the total Cd content and available CD content in the whole soil profile were the highest in paddy soils developed from river and lake sediments,followed by limestone weathering products,purple sand shale weathering products,Quaternary red clay,plate and shale weathering products,and the lowest was in paddy soils developed from granite weathering products.Parent material type strongly affects the Cd content in paddy soils.(2)Among the 25 paddy soil species,the total Cd content and available Cd content in the whole soil profile were the highest in river mud,and the lowest in river sand mud and hemp sand mud.In the 4 subgroups of rice soils,the total Cd content and available Cd content in the soil profile were highest in the redox paddy soils(the total Cd content was 0.221 mg/kg,the available Cd content was 0.152 mg/kg),followed by the flooded paddy soils,and the the lowest in the bleaching paddy soils and the gleying paddy soils.The type of paddy soil has a significant effect on soil Cd content.(3)From the perspective of soil layer,the Cd content of soil decreased with the increase profile depth,with the highest total Cd content and available Cd content in layer A,followed by layer B,and the lowest in layer C.The distribution of available Cd in soil profile is similar.The proportion of available Cd in soil in layer A was the highest(48%),followed by layer B(32%),and the lowest in layer C(23%).(4)The correlation analysis showed that the total Cd content and available Cd content in soils were positively correlated with soil organic carbon content and silt content,negatively correlated with sand content,and not significantly correlated with clay content,p H value and free iron content.Redundancy analysis showed that soil organic carbon,silt and sand were the main physical and chemical indexes that determine the total Cd content and the available Cd content in paddy soils.