Effects Of Residual Plastic Film Amount On Water Infiltration And Redistribution In Drip Irrigation

In recent years,the combination of drip irrigation technology and plastic mulching has presented a leap forward development in the arid areas of northern China,but the"white pollution"caused by agricultural film residues has become more and more serious.With the accumulation of residual film year by year,it will not only affect soil physical properties and soil air permeability,but also affect the process of soil water infiltration and redistribution,and ultimately affect crop growth.It is important to study the soil water infiltration and redistribution in the residual film contaminated area to guide the drip irrigation mode.In this paper,the effect of residual film on soil water infiltration under drip irrigation was studied by using the method of indoor soil box simulation.The experiment analyzed the effects of different residual film content,initial water content,soil bulk density and dripper flow rate on the soil wetting process,investigated the influences of different residual film content on soil infiltration aspect ratio,infiltration rate and stable infiltration rate,shape and size of wetting body and water content distribution,and analyzed the effects of soil water redistribution under the condition of the residual film content of 360 kg/hm~2.The main research results are as follows:(1)In the same infiltration time,the horizontal and vertical migration distances of the wetting front increase with the increase of the initial soil water content and the dripper flow rate;as the increase of soil bulk density,the horizontal wetting front migration distance is greater,and the vertical wetting front migration distance is smaller;the residual film can promote the horizontal migration of wetting front and hinder the vertical migration to some extent,the residual film content is positively correlated with horizontal migration distance and negatively correlated with vertical migration distance.(2)The migration distance of wetting front is in a power function with the infiltration time,and the horizontal and vertical infiltration coefficients are linear with the initial soil water content,soil bulk density,dripper flow rate and the residual film.The power index coefficients are 0.28 and 0.45 respectively,and the fitting results of each function are all above 0.86.The comprehensive prediction model of wetting front distance under the combination of four factors has higher precision and the coefficient of determination is above 0.90.(3)The soil aspect ratio is greater than that at the beginning stage of infiltration,and the aspect ratio of different residual film treatments decreases significantly within 60-300min.The aspect ratio of residual film treatments is larger than that of non-residual film treatments,and it is positively correlated with the amount of residual film.When the residual film content is more than 180 kg/hm~2,the aspect ratio is more than 1.0 after infiltration.At this time,the soil is suitable for planting shallow root crops,and the aspect ratio has a power function relationship with the infiltration time.(4)The influence of residual film on the infiltration rate is mainly reflected in the initial stage of infiltration,which has little effect in the middle and late stages.At the end of infiltration,the infiltration rate of each treatment reaches a stable value,and the existence of residual film improves the steady infiltration rate of soil water.Compared with the fitting results of Kostiakov model,Philip model and Green-Ampt model,the Kostiakov model has strong applicability.(5)The shape of wetting body is 1/4 semi-ellipsoid and its size is positively correlated with the amount of residual film.In non-residual film treatment,the shape of wetting body is relatively smoother,but presents different degrees of irregularity with the increase of the amount of residual film in the treatment containing residual film.The distribution of water content in wetting body decreases gradually from the center of dripper to the edge of wetting front,and the contour is densely distributed in the middle layer of soil.The more residual film is,the lower the average water content of the wetting body is.Meanwhile,the optimum growth depth of crops increases with the increase of residual film content,which is not suitable for planting deep root crops.(6)At the beginning of evaporation,the soil water content decreases rapidly,then slowly and the surface water content decreases rapidly,while the middle and lower layers decreases slowly.As the prolongation of evaporation time,the position of higher water content in the wetting body moves gradually from near the dripper to directly below the dripper.The presence of residual film increases the uncertainty of the redistribution process of soil water content.Under this conditions,the contours of soil water content appear irregular or even closed to varying degrees and the water content may increase or decrease locally,especially in the left half of the wetting body.