Abstract:
Abstract: The residual plastic film in soil inevitably affects soil hydrodynamic parameters, reducing the soil infiltration capacity, and seriously influences soil water and solute transport which is closely connected with soil water characteristic curve (SWCC). In order to study the effects of different residual film amounts on soil water retention ability, 5 residual film treatments (0, 50, 100, 200, 400 kg/hm2) were conducted to measure SWCC based on the pressure plate extractor test; A new model of soil water characteristic curve with residual plastic film (RPF-SWCC) was constructed, and its performance was evaluated by parameters such as root mean square error (RMSE), geometric mean (GMER) and coefficient of determination (R2).The results showed that the ability of soil water retention decreased gradually with the increase of residual film amounts. The higher amount of residual plastic film would produce the lower soil moisture under the same suction condition, especially the high suction condition. For example, when the suction reached to its maximum (700 kPa), the soil moisture of residual film treatment (400 kg/hm2) was only 79.58% of non-residual film treatment. With the increase of residual film, the equivalent aperture ratio was increased in the low suction stage (mainly draining soil water in large pore). On the contrary, it was decreased in the high suction stage (mainly draining soil water in medium and small pore). The equivalent aperture for large pores in the low suction stage was between 0.00300 and 0.15000 mm, and the equivalent aperture for medium and small pore in high suction stage was between 0.00043 and 0.00300 mm. When the residual film reached to 400 kg/hm2, the equivalent aperture ratio of the low suction stage increased by nearly 20% over the non-residual film treatment. In general, the SWCC fitting accuracy of van Genuchten (VG) and Log normal distribution (LND) model was higher than that of Brooks Corey (BC) model for the soil with residual film. VG model was more suitable for low residual film soil, and LND model was more suitable for high residual film soil. The RPF-SWCC model had a higher accuracy than van Genuchten (VG), Brooks Corey and Log normal distribution model. The RMSE, GMER and R2 of the RPF-SWCC model were all better than the other models, and the RMSE for 2 high residual film treatments (200, 400 kg/hm2) were reduced 24.3% and 65.0%, respectively compared with the VG model; In addition, the parameters of RPF-SWCC model showed that the saturated soil water content decreased with the increase of residual plastic film, and the residual soil water content increased with the increase of residual plastic film. So, it can be concluded that RPF-SWCC model had better performance for fitting soil water characteristic curve with residual plastic film. The study can provide valuable information for development of soil water modeling and high efficient utilization of water and fertilizer in the residual plastic film area.