Effects of plastic film mulch on the soil wetting pattern, water consumption and growth of cotton under drip irrigation

The index of soil wetting pattern is essential to the design of drip irrigation(DI). Field experiments were carried out to study the characteristics of soil wetting pattern for mulched drip irrigation(MDI) technique by comparison with the DI technique. In the experiments, soil moisture content in field was observed and analyzed as well as the soil water consumption and the characteristics of cotton growth, such as cotton stem high, leaf area index (LAI), cotton yields, and so on. Results show that, when the field surface is mulched by plastic film, the whole mulched area of field is irrigated, and the ratio of soil wetted area for the MDI is larger than that for the DI. The fact that the film covering over field resists soil saturation pond beneath dripper to expand to the soil out of the film, resulted in the soil moisture content out of the film being so low that soil water consumption for the MDI is lower than that for the DI within the area irrigated by a drip line. Water utility rate for the MDI is larger than that for the DI. But this fact causes the cotton, which is planted near by side of film, being unsatisfied growing compared with the cotton planted at the middle of film. In addition, the index of soil available moisture (ISAM) is used to assess the soil wetting pattern to clearly express the relationships between soil wetting pattern and crop water consumption. Thus the ISAM could be usable for designing the ratio of soil wetted area.