Abstract: The study area is located in the Yaoba Oasis irrigated area in the Alxa League of Inner Mongolia.Based on the field investigation,in this paper the distribution of total salt and salt ions in topsoil samples collected from the Yaoba Oasis was analyzed using the descriptive statistical method,correlation analysis and principal component analysis (PCA).According to the descriptive statistical analysis,the results showed that the topsoil in the oasis is alkaline chlorine-sulfate salinized soil.The cations in topsoil were dominated by Ca²⁺ and K⁺+Na⁺,and HCO₃^- was dominant in anions.The total salt content in topsoil was high in the southwest but low in the northeast.Total soil salt content varied obviously from the east to the west but slightly from the south to the north.In topsoil,the variability of salt ions of HCO₃^-,K⁺+ Na⁺,SO₄^2- and Cl^- was strong,that of Ca²⁺,Mg²⁺ and HCO₃^- was moderate,and that of pH value was slight.The correlation analysis revealed that there were the extremely significant positive correlations between total soil salt content and SO₄^2-,Ca²⁺,K⁺+Na⁺,Cl^- and Mg²⁺,and the correlation coefficient between total soil salt content and SO₄^2- was the highest (0.958).There were the extremely significant negative correlations between total soil salt content and Mg²⁺,Ca²⁺,Cl^- and SO₄^2-,and all the correlation coefficients were lower than 0.6.According to the PCA,there were two principal component factors,and they could be used to reflect the salt content in topsoil in the study area.One could be used to reflect the soil salt component,and another could be used to reflect the soil alkalinity,so it was concluded that SO₄^2-,K⁺+Na⁺,Ca²⁺ and Cl^- could be used to characterize soil salinization.Moreover,the equations of comprehensive scores of the principal components were developed.According to calculated results of comprehensive scores of 42 soil samples,the values ranged from 3.6 to 10.7,the average value was 5,and the standard deviation was 1.5,so the variability was moderate.The study results could provide the theory and practical basis for preventing and controlling soil salinization and for safe development of agriculture and animal husbandry in the study area.

Key words: topsoil, soil salt content, principal component analysis, Yaoba Oasis, Inner Mongolia