| In order to improve the sustainable use of gravel-sand mulched fields in the arid area in central Ningxia, the soil enzyme activities and soil physiochemical properties of continuous cropping (1 a, 3 a, 5 a, 7 a, 10 a) were examined in the soil cultivated with selenium-contained watermelon in Hong Juanzi Village, Xingren County of Ningxia Hui Autonomous Region. The resulting data was analyzed by the methods of One-Way ANOVA and Pearson correlation analysis and principal component analysis, providing the trend of sand soil quality upon the increase of years of continuous cropping. The results showed that activities of soil enzymes (urease, neutral phosphatase, invertase, and catalase) displayed declining trends with the increase of years of continuous cropping. Those of urease, invertase and catalase showed significant negative correlations with soil bulk density, but exhibited significant positive correlations with soil porosity. Soil physical properties turned to be poor quality gradually with the increase of years of continuous cropping, and soil moisture reached a maximum value in 5 years of continuous cropping. Soil fertility became decreased gradually and the contents of total salt were decreased significantly. The highest comprehensive score of soil quality was 0.96 in 1 year, and the lowest was -0.8 in 10 years. There was an obvious obstacle of continuous cropping between 5 years and 7 years. Therefore, to ensure the sustainable use of sand soil, scientific and rational fertilization and tillage needed to be carried out. |