Distribution and movement characteristics of soil water and soil salt during evaporation from perforated plastic mulch

In arid and semi-arid area of Xinjiang region, the plastic mulch irrigation area is increasing year by year. In fact, no entire mulch can be performed in the field, and planting film holes and irrigated film holes should be added in order that plant may merge and water can infiltrate into the soil. So it is necessary to study the characteristics of soil water and salt movement under plastic mulch during evaporation with different open hole ratios. In this paper, for the observation of soil water content and soil salt distributions during evaporation from perforated plastic mulch, experimental 1-dimension vertical infiltration-evaporation system was set up. In the experiment system, the soil columns were double-layer Plexiglas, soil water was observed dynamically using -ray attenuation method, and soil salt-conductor was used to measure soil salt content. Two treatments were adopted including evaporation with initial uniform soil water content and soil salt content and evaporation after infiltration. Observations of soil salt content distribution and soil salt concentration (ratio of soil salt content to soil water content) distribution were analyzed for evaporation from perforated plastic mulch at different open hole ratios. In the treatment of evaporation with initial uniform water and salt contents, a good relationship was found between soil salt concentration and soil water content at different open hole ratios, while in the treatment of evaporation after infiltration, different functions were used to describe the relationship of soil salt concentration and depth at different open hole ratios. The increased salt content accumulated at 10cm top layer was increasing with the (increasing) of open hole ratios. And the increased salt content accumulated at 10cm top layer on unit film hole area was powerful function of open hole ratios, while at the same open hole ratio, the increased salt content accumulated at 10cm top layer in the treatment of evaporation with initial uniform water and salt contents was much higher than the treatment of evaporation after infiltration, which indicated that the de-salt effect of infiltration not only played roles in the stage of infiltration, but also in the later evaporation stage. Moreover, there was fine linear relationship between the cumulative (evaporation) on unit film hole area(ER) and the increased salt content accumulated at 10cm top layer on unit film hole area(Wsm,10).