Study On The Influence Of Residual Plastic Film In Farmland On Soil Water Flow

China is a large agricultural country and ranks first in the world in the use of agricultural plastic film.agricultural plastic film can increase temperature,retain water,prevent insects and reduce weeds,and can improve crop yield and quality.Therefore,agricultural plastic film has become another important production material after seeds,fertilizers and pesticides.However,the lack of mechanisms and policies for recycling agricultural plastic film,coupled with the difficulty of self-decomposition of agricultural plastic film in the soil,has led to the growing problem of agricultural plastic film residues in the soil.The residual plastic films in agricultural soils changes the physicochemical properties of the soil and affects water retention and movement in the soil,which in turn affects the growth and yield of crops.To address this issue and to characterize the distribution of residual plastic films in China,this paper investigates the effects of residual plastic films content(75 kg/hm2,150 kg/hm2,300 kg/hm2),residual plastic films burial depth(0-5 cm,0-10 cm,0-20 cm)and residual plastic films size(1 cm × 1 cm,2 cm× 2 cm,4 cm × 4 cm,1 cm × 4 cm)on water retention and movement in the soil,and the simulation of heterogeneity water movement processes in residual mulch farmland using an active region model.The main research results are as follows:(1)The retention effect of residual plastic films on irrigation water increases with the increase of residual plastic films content;when the residual plastic films content was greater than 150 kg/hm2,the water content of the residual plastic films layer was significantly greater than the water content of the soil layer at the same depth in the blank test;the stagnant effect of plastic films on irrigation reduces the heterogeneity of infiltration water movement in the residual plastic film.The heterogeneity of infiltration water flow also showed a trend of increasing with the increase of residual plastic film content.(2)In the case of the same residual plastic films content,the greater the thickness of the residual plastic films layer,the smaller the amount of residual plastic films per unit volume,the less likely residual plastic films is to overlap into rolls,the stronger the residual plastic film’s blocking effect on irrigation water,the lower the heterogeneity of infiltration water movement,and the smaller the maximum infiltration depth of irrigation water(3)Under the same conditions of residual plastic film content,both too small(such as 1 cm× 1cm)and too large(such as 4 cm × 4 cm)size of residual plastic film will increase the heterogeneity of soil water flow;The total amount of residual film is increased,and the latter is duc to the excessive size of the residual plastic film,which causes itself to be rolled or folded to form a preferential flow pipe.When the residual mulch fragments have the same area but different shapes,the elongated mulch fragments are more likely to induce the formation of soil preferential flow than the square mulch fragments.(4)Residual plastic film reduces the residual moisture content and saturated moisture content of the soil.The distribution of soil moisture content and the distribution of dyeing area in the mulch residual farmland simulated by the active region model are consistent with the measured data,indicating that the model can be used to predict the water distribution and water flow process in the mulch residual farmland.