Relationships between soluble salt content and electrical conductivity for different types of salt-affected soils in Ningxia

Based on distributing areas of the salt-affected soils in Ningxia,141 soil samples of surface layer in 0～20 cm with different types of salt-affected soils from various regions of Ningxia were collected,respectively.The electrical conductivities of the soil extracts by using 5∶1 of the ratio of water to soil and the content of soil soluble salts were determined with residue-drying method.The relationship between soluble salt content by residue-drying method and the electrical conductivity in the soil extracts was studied.The results are as follows:(1) The ionic components of the soluble salt for tested soils were proved up.The Na+ content was the highest and Ca2+ and Mg2+ contents were higher in 4 cations.The Cl-content was the highest and SO42-content was quite high in 4 anions.(2) The classifying standard of salt component types for the salt-affected soils in Ningxia Province was perfected.The salt component types for the salt-affected soils were found out.In anion components,the types of sulphate-chloride,chloride-sulphate and sulphate were dominant.In cation components,the types of Mg-Ca,Ca-Mg and Na were dominant.(3) The regressive equations between the soluble salt content and the electrical conductivity for salt-affected soils of different types in Ningxia were obtained.The optimal regressive equation between soluble salt content by residue-drying method and the electrical conductivity had been screened out from 5 kinds of function patterns.When the soil salt component types were not differentiated,the soil salt content was calculated by using the formula of y=0.1609x2+2.9176x-0.0141.While the soil salt component types have been known,the soil salt content was calculated by using the optimal regressive equations of different salt types.(4) The revised equations of the content of soil soluble salts from an electrical conductivity method to residue-drying method were put forward.The method will supply a scientific basis for testing exactly and rapidly the contents of soil soluble salts.