Effects Of Biodegradable Plastic Film On Plant And Soil Properties

Plastic film mulching technology significantly improves the yield and water efficiency of grain crops by maintaining water,keeping moisture,inhibiting weeds and increasing temperature.However,the commonly plastic film material is polyethylene material,the accumulation of residual film leads to soil fertility degradation,which has become a major challenge for the sustainable development of agriculture,which has caused a series of environmental and ecological problems.Research shows that biodegradable plastic film is one of the effective ways to solve the problem of white pollution,but its impact on soil-plant system is not clear.In this study,pot experiment was used to study the effects of different dosages(2.5,10 and 40 g·kg^-1)of biodegradable plastic film raw material particles whose main components are butanediol adipate and butanediol terephthalate（PBAT）and polylactic acid（PLA）from three domestic enterprises（X,S and H）by testing growth,nutrient transport and absorption of wheat（Triticum aestivum L.）and soil properties;The other pot experiment was used to study the effects of different dosages(2.5 and 10 g·kg^-1)of PLA+PBAT biodegradable plastic film fragments from five enterprises（X,S,Q,H and J）by testing growth,chlorophyll content,nutrient absorption and transport of ryegrass（Lolium perenne L.）and soil properties.On this basis,the residue of phthalate esters（PAEs）in soil about biodegradable plastic film fragments was analyzed in order to provide a basis for the safety evaluation of large-scale application of biodegradable plastic film.The results showed that:（1）Biodegradable film raw material particles significantly increased soil p H,but had no significant effect on soil organic matter content;medium,high dosage of H and low,medium dosages of S plastic particles had positive effect on soil nitrification and soil nitrogen availability,while X film particles had inhibitory effect;H film particles increased soil available phosphorus content,S and X had no significant effect;X film particles increased the content of soil available potassium,but S and H had no significant effect.The activities of catalase,urease and sucrase decreased with the increase of the dosages of plastic film particles,at high dosage,the activities of urease and sucrase decreased significantly.For wheat growth,except for the low and medium dosages of S treatment,the other treatments inhibited the growth of wheat,in which X film particles had the greatest inhibitory effect on the biomass of wheat roots,stems,leaves and grains,and with the increase of the dosages of film particles,the inhibition effect of wheat biomass was more obvious.For wheat nutrients,the absorption of nitrogen was promoted at low dose,inhibited at high dosage,and the three kinds of film particles inhibited the absorption of phosphorus and potassium.Three kinds of plastic film particles inhibited the transport of nitrogen to grains and promoted the transport of phosphorus to grains,but it had no obvious effect on the transport of potassium Correlation analysis showed that wheat biomass was the main factor affecting wheat nutrient accumulation.（2）PE and biodegradable film fragments increased soil p H and the contents of inorganic nitrogen,available phosphorus,available potassium.Biodegradable film fragments significantly increased the content of soil organic matter,but PE film fragments had no significant effect;PE film fragments decreased soil urease activity,while biodegradable film fragments increased soil urease activity.Both of them significantly increased soil catalase activity,but there was no significant difference in soil sucrase activity;Film fragments had little effect on the content of soil dissolved organic matter（DOM）,but it increased the average molecular weight of soil dissolved organic matter and the content of non-polar functional groups such as fats and esters contained on benzene ring substituents.meanwhile it reduced the aromatization degree of soil dissolved organic matter,the content of hydrophobic components,the content of aromatic amino acids of conjugated double bonds.The endogenous microbial activity of dissolved organic matter became stronger,but the degree of humification became slower.For the growth of ryegrass,PE film fragments inhibited root growth but it promoted stem and leaf growth,while biodegradable film fragments inhibited the root growth of ryegrass.The inhibitory effect on stem and leaf growth of ryegrass varied with harvest times,film types and film dosage:the inhibitory effect decreased with the increase of harvest times;J plastic film treatment had the most obvious inhibitory effect;The inhibitory effect of the same plastic film treatment on ryegrass was high dosage>low dosage.The correlation analysis showed that the biomass of ryegrass was the main factor affecting the nutrient accumulation of ryegrass.（3）Plastic film fragments increased the contents of DMP,DEP,Dn BP,Di BP,DEHP monomers in soil,and the total value of five monomers increased by 0.49～4.75 mg·kg^-1.Compared with PE film,biodegradable film fragment may have a higher risk of phthalate residue,and the content of phthalate monomer increases with the increase of the dosages of film fragments.In general,the biodegradable plastic film particles and fragments have a certain negative impact on the plant-soil system.The degree of impact varies with the type and dosage of plastic film particles or fragments.And the biodegradable plastic film fragments will leave phthalate monomers.So,it is suggested to strengthen the study on the coupling relationship between the degradation dynamics of biodegradable plastic film particles and fragments,meanwhile it is vital to study the availability of soil nitrogen,phosphorus and potassium nutrients,the number and composition of soil microorganisms and crop growth,so as to provide a basis for the comprehensive evaluation of the environmental impact of biodegradable plastic film.