Effects of agricultural plastic film residues on transportation and distribution of water and nitrate in soil

Residual plastic film in soil destroys the soil structure and changes the normal transportation and distribution of water and nutrient. In this work, we compared experiments on soil containing residual plastic film with a control experiment to investigate how residual film affects the transportation and distribution of water and nitrate (NO3-) in wetted soil. The experiment used Mariotte bottle, water tube, and soil tank to test six levels of residual-film concentration varying from 0 to 720 kg/hm2 in the soil. The wetting front, soil water content, and nitrate concentrations were all measured, and the results showed that when the concentration of residual-film was less than 360 kg/hm2, more water and nitrate remained in the upper part of the wetted volume due to block of residual film. Excessive residues (>360 kg/hm2) resulted in obvious phenomenon of preferential flow, which increased the wetting distance, wetted volume, and water content in the lower part of the wetted volume and the concentration of nitrate at the boundary of the wetted volume. These results not only help us to understand the consequences of plastic-film-residues pollution in terms of water and nitrate movement, but also provide scientific support to the development and establishment of reasonable irrigation, fertilization and management systems for polluted farmland with differential mulch residual concentrations.