Abstract: Soil salinity sensors were used in the field plot experiments to monitor the salinity variation of soil solution at different depths. The field plot experiments were carried out in the farmland covered by plastic film, wheat straw and uncovered. The results are as follows： (1) The salinity increases sharply during the period without irrigation but reduces quickly during irrigation in both surface soil and soil solution 10 cm deep from the top. The variation of salt content is relatively smooth in the farmland covered by plastic film or wheat straw comparing with that in the uncovered farmland. (2) The salinity of soil solution 30 cm deep from the top also increases during the period without irrigation but reduces during irrigation. However, it reduces in the farmland covered by wheat straw after the first irrigation, and reduces slowly and keeps a low level after the first irrigation in the farmland covered by plastic film. (3) The salinity variation of soil solution 60 cm deep from the top is gentler than that of the overlying soil layers. The salinity of soil solution of this layer in farmland covered by straw reduces more sharply than that in formland covered by plastic film and the uncovered farmland during irrigation but increases more slowly during the period without irrigation.

Key words: straw cover, plastic film cover, soil solution, electric conductivity