Characteristics of air temperature and water-salt transfer during freezing and thawing period

Freezing and thawing action is a particular mechanism of soil salinization in the northwestern arid and cold area. Taking Inner Mongolia Hetao Irrigation District as an example, based on the observed field data, the variation laws of soil temperature, soil moisture and soil salt during freezing and thawing period were analyzed. Results show that the variation laws of soil temperature at the different soil layers are consistent. Variation of soil temperature lags to air temperature. With the soil depth increasing, lag interval increases also. Decrease of air temperature results in that of soil temperature, which leads to water and salt transfer. Temporal variability coefficient of salt(0.30～0.85) is larger than that of water(0.02～0.40). Salt transfer mechanism is more complex than water transfer mechanism. Research provides the foundation for the water-heat-salt coupling simulation on freezing-thawing soils and the establishment of autumn irrigation schedule in Hetao Irrigation District.