Abstract:

In order to study the variations and correlations of moisture, salt, pH and urease activity in soil layers of 0-50 cm of paddy under freeze-thaw action, the soil samples were collected from paddy of Da’an City which is in the area of saline-alkaline soil in western Jilin Province. A freeze-thaw cycle of the indoor simulating experiment was freezing for 12 hours and thawing for 12 hours to simulate the transport of water and salt and the dynamic changes of soil enzyme activities under the repeated freezing and thawing condition in day and night. Then soil moisture content, salt content, pH and urease activity were tested by mass method, residue drying method, potentiometry and indophenol blue colorimetry respectively to analyze the variation law and the correlations under different freeze-thaw conditions. The results show that the depth of soil layer is one of the main influencing factors of moisture content, salt content, pH and soil urease. The moisture and salt in soil layers of 20-50 cm transfer continuously to the surface layer and moisture content shows significant correlation with salt content, which suggests that salt transfer is determined by moisture transfer to some extent. Except for the layer of 10-20 cm, soil urease activities in all layers decrease at different degrees. In frozen-thaw process, moisture content, salt content and pH all show significant correlations with soil urease activity. And soil urease activity is affected by many factors such as the number of freeze-thaw cycles, temperature, salt content, pH, organic matter and other related factors. Therefore, freeze-thaw action plays a crucial role in causing or aggravating the salinization of paddy topsoil. Freeze-thaw action results in the decrease of urease activity, which will further affect the soil fertility.

Key words: freeze-thaw action, pH, water-salt transfer, soil salinization, soil urease, western Jilin Province