Variation of soil temperature in cotton field covered with plastic film under saline water irrigation

Changes of soil temperature in cotton field covered with plastic film under saline water irrigation were investigated by plot trial. Results showed that saline water irrigation produced a certain influence on soil temperature by changing ground coverage. Soil temperature in the rows with film mulching (RFM) was higher than that in the rows without film mulching (RNFM), especially at seedling stage and in the 5~10 cm soil layer. The daily variation of soil temperature in different positions fitted sinusoidal curve approximately. With the increase in soil depth, the process of soil temperature change became steady, and the appearance time of peak value delayed. During the growing season, the average daily soil temperature in different soil depths in RFM and RNFM was linear positively related to the near-surface air temperature, and the correlation coefficients reached extremely significant level (P<0.01). For one day, if the time-lag effect between soil temperature and air temperature was corrected, the relationship between the soil temperature in different soil depths and the near-surface air temperature gave a good fitted to linear regression equations, and the correlation coefficients reached a significant level (P<0.05). The experimental results provided a theoretical basis for the building of water-heat-salt transfer model and the regulation of water-salt distribution.