Effects of different residual plastic film quantities in soil on drip infiltration and its uncertainty analysis

Abstract: The quantities of residual plastic film in soil will further increase with the wide application of agricultural plastic mulching film, and the residual plastic film in soil will not only influence soil water movement, but also lower the infiltration properties. In the study, the experiments with six treatments and Three-time repetition were carried out in Huhhot,China, which included three kinds of cumulative quantities of residual plastic film (0, 5, 20 kg/hm-2), and two kinds of dripper discharges (0.5 and 2 L/h). The effects of different cumulative quantities of residual film and different dripper discharge on the drip wetting front and wetting patterns were studied by experiments and mathematical analysis, and the uncertain infiltration model was proposed on the basis of Kostiakov infiltration model, and the uncertainties of infiltration rate for different cumulative quantities of residual film treatments were quantitatively analyzed and compared using Bayesian analysis. The results showed that migration distances of drip wetting front decreased significantly with the increase of residual film for all treatments in the same period of time, especially that the effect of residual film on migration distance of drip wetting front in vertical direction were more significantly different (p<0.01) for high dripper discharge in the phase of soil water redistribution. When cumulative quantities of residual plastic film increased in soil, the drip infiltration rate would significantly slow down, which caused that the drip wetting patterns were smaller, and the drip wetting patterns of vertical direction under residual plastic film treatments were 10%-20% lower than that under the non-film treatment. In the meantime, cumulative quantities of residual plastic film had irregularly changed for the wetting patterns in the residual film region between 10 and 20 cm soil layer, and the more cumulative quantities of residual plastic film, the more irregular variety for wetting patterns. As the residual film increased, the posterior parameters standard error of uncertain infiltration model based on Kostiakov model apparently increased, and 95% posterior distribution interval were also enlarged using Bayesian analysis, and the effect of infiltration uncertainties for high dripper discharge (2 L/h) were more significant, which explained the augment of cumulative quantities of residual plastic film and increased the uncertainties of infiltration rate because of randomness of residual film location and the uncertainties of mixing compactness between residual film and soil. In conclusion, agricultural plastic mulching film would increase uncertainties of drip infiltration.