Effects Of Residual Plastic Film Amount On Soil Water Movement And Growth Of Tomato Planted In Greenhouse

Plastic film could increase soil temperature and soil water content,raise soil water capacity and restrain salt,improve soil micro-climate,reduce soil erosion,adjust soil water fertilizer gas heat,which is conductive for crop growth.Plastic film is widely spreaded and used in north China,application amount and covered area have a rising trend.But the thickness of plastic film widespread is 0.008 mm.The tensile load of plastic film is low,easy to broken,residual film mechanical recovery rate is low,which lead to the amount of residual plastic film increases with increasing years of laminating.In additions,the negative effects of residual plastic film on soil-crop ecosystem is highlighted.Faced with current situation of increasingly severe residual membrane contaminated,soil boxing experiment,soil column experiment and tomato planting experiment were conducted.Based on these experiments,we explore the effects of residual plastic film on soil water infiltration,horizontal movement,evaporation and tomato growth.This study could provide a viable theoretival basis for formulating irrigation scheme and crop scheme in area polluted by residual plastic film.The main results of this study are as follows:1)Residual plastic film prolonged infiltration time,and the consuming time that water infiltrate to 45 cm increased with increase of residual plastic film.The infiltration rate curve of treatments containing residual plastic film would separate with control treatment T0 when water infiltrated to a certain depth.Separated time was shortened and logarithmically decreased.Compared with Philip model and Green-Ampt model,Kostiakov infiltration model was more suitable to simulate the process of water infiltration in soil containing residual plastic film.Wetting front moving distance increased exponentially with the prolonging of infiltration time,while there was negative correlation between wetting front moving distance and accumulative quantities of residual plastic film.Residual plastic film had an adverse effect on the process of soil water infiltration,which the disadvantageous effect would aggravate with the increment of residual plastic film.2)Residual plastic film would not only reduce the transport velocity of vertical wetting front,but also decrease soil cumulative infiltration.When the amount of residual plastic film was more than 80 kg/hm2,transport velocity of wetting front decreased dramatically.As the amount of residual plastic film increased,consumed time that wetting front arrived at 40 cm significantly prolonged(F=19.11,P<0.05).On the other hand,cumulative evaporation significantly decreased when the amount of residual plastic film was more than 160 kg/hm2(F=9.58,P<0.05).However,evaporation coefficient increased with the increment of residual plastic film,which indicated that the water holding capacity of soil decreased.Residual plastic film also changed the distribution of soil moisture.As the amount of residual plastic film increased,gravimetric soil moisture decreased at the 0~10 cm and >20~45 cm depth.At 0~10 cm depth,variable coefficient of soil moisture increased by 4.33%,127.19%,330.40%,539.63% and 640.23% compared with that for T0 treatment,respectively.Moreover,the variable coefficient had a trend of decrease at >20~45 cm depth.This implies that the inhomogeneity of soil water distribution was enhanced due to residual plastic film pollution.Moreover,soil surface hardened when the amount of residual plastic film was more than 320 kg/hm2.As the amount of residual plastic film increased,the 95% confidence interval and standard error of posterior parameters all increased for the Kostiakov infiltration model and Rose evaporation model according to Gibbs sampling algorithm.The areas of posterior distribution intervals of cumulative infiltration and evaporation also increased.In general,residual plastic film could increase the uncertainties in soil water infiltration and evaporation.3)The migration rate of horizontal wetting front,the accumulative infiltration amount and volumetric soil water content gradually declined with the increase of residual plastic film amount.When residual plastic film amount was more than 160 kg/hm2,the migration rate of horizontal wetting front and the accumulative infiltration amount would dramatically reduce.There were extremely significant positive correlation relationship between the amount of residual plastic film and retardation coefficient.When the amount of residual plastic film ranges from 80 kg/hm2 to160 kg/hm2,increase rate of retardation coefficient reached up to 251.15%.The distance from stronger retardation region to infiltration point was enlarged with increase of residual plastic film.However,Boltzmann coefficient and water diffusivity were gradually declined,driving force of soil matric potential on soil water diffusion and soil water holding ability wore off.The horizontal diffusion process of soil mixed with residual plastic film still conforms to single parameter model of soil water diffusivity.4)Residual plastic film hindered the growth of tomato root at both seedling and blooming and fruit-setting stages.Root volume,root length density and root dry weight density decreased with increasing residual plastic film amount.In addition,as the amount of plastic film residue increased,plant height and stem diameter decreased significantly(P < 0.05).Besides,the rates of increase in plant height and stem diameter decreased with increasing residual plastic film amount.Logistic model accurately simulated the growth process of tomato in fields with residual plastic film less than 1 280 kg/hm2(R2 > 0.87).As the amount of residual plastic film increased,beginning period and full period of tomato biomass accumulation was ahead of time.This implied that the suitable time of fertilization of tomato should be brought forward.Overall,biomass accumulation decreased for the whole tomato growth period.Contrary to biomass accumulation of leaf,that of root,stem,flower and young fruit decreased with increasing residual plastic film amount.The hindering effects of residual plastic film on tomato growth and dry matter accumulation at seedling stage were higher than at blooming and fruit-setting stage.The early period and middle period of tomato biomass accumulation all occurred in advanced.