Degradation And Pollution Characteristics Of Different Types Of Agricultural Film And Their Effects On Soil Physicochemical Properties

As an important agricultural cultivation technique in arid and semi-arid areas,mulch cultivation can effectively improve crop yield and quality,thus improving economic benefits.However,the extensive use of plastic mulch has caused many environmental problems.As one of the main ways to solve the residual agricultural film,biodegradable mulching film has been widely concerned.However,most of the studies were done under laboratory simulation conditions,and the mulching film involved was mostly composed of a single component.For actual farmland soil,the influence mechanism of degradable mulching film covering on soil physical and chemical properties,crop growth conditions and its potential environmental effects still need to be explored.Therefore,this paper systematically studied the effects of different types of mulching film on the physicochemical properties(moisture,temperature and nutrient content)of farmland soil,and further clarified the effects of mulching film mulching on maize yield index.On this basis,the degradation performance of different types of mulching films in farmland soil was clarified through field observation and classification and Fourier infrared spectroscopy.Due to the great difference in degradation performance between degradable and non-degradable mulching films and the fact that degradable mulching films can be decomposed to the size of microplastics,the mulching films are classified into two categories,which are both degradable and non-degradable,and the microplastics pollution in soil after mulching is simply analyzed.At the same time,the effects of different types of mulching film residue on soil physicochemical indexes and microbial community characteristics were explored through field culture experiments with different types and amounts of mulching film residue,so as to comprehensively analyze the service performance and possible environmental impact of different types of mulching film residue.The main research results are as follows:(1)Mulching film can significantly increase soil surface temperature and moisture content,and then affect soil respiration rate.Mulching treatment could increase the average soil surface temperature by 0.59～2.24 ℃ and the soil surface water content by 0.38%～3.02%during the whole cultivation period of maize.The thermal insulation effect of mulch film is mainly related to the material and color of mulch film,while the water retention performance has no obvious relationship with color.Mulching film can increase the nitrate nitrogen content of soil surface and slightly increase the p H value of soil.In addition,mulching significantly enhanced soil respiration rate,which was mainly related to soil moisture content.(2)Mulching treatment could significantly improve plant height,100 grain weight,yield and economic benefit of maize at harvest stage.Compared with bare land,the plant height,100 grain weight and aboveground dry weight of maize in harvest period increased by3.68%～14.73%,7.71%～26.77% and 9.61%～41.89% respectively.Black full-biodegradable mulching film had the best lifting effect.The height of short-time full-biodegradable black film and long-time full-biodegradable black film increased by 14.73% and 11.90% compared with that of non-mulching film treatment.100 grain weight increased by 22.52% and 26.77%.At the same time,the economic benefit of short-time biodegradable black film is higher than that of ordinary mulch,while the economic benefit of other biodegradable mulch is lower than that of ordinary mulch.(3)The degradation performance of different types of mulch films is different.Among degradable mulch films,the induction period of transparent mulch film is shorter,the induction period of short-time biodegradable transparent film is 20 d,the induction period of short-time biodegradable black film is 60 d,the induction period of long-time biodegradable transparent film is 45 d,and the induction period of long-time biodegradable black film is 60 d.This indicates that color is one of the factors affecting the induction period of degradable mulch.The integrity of non-degradable plastic film was the best in harvest period,while the integrity of short-time biodegradable transparent film was the worst.The absorption peak of fat bond was produced in common mulching film,that is,oxidation occurred.No new absorption peak was formed in biodegradable mulching film,and the overall lipid bond absorption peak decreased.The degradation mechanism may be lipid bond hydrolysis.Plastic mulching can cause microplastic pollution in different degrees,and the pollution status is related to the type of plastic mulching.The detected microplastics in the mulch covered field soil ranged in abundance from 0 to 35 items/kg,in size from 0.9 to 4.8 mm,in color mainly blue and black,and in shape mainly fibrous.(4)Residual plastic film can affect soil organic matter,total nitrogen,available phosphorus,available potassium,p H and soil bulk density,and also affect soil bacterial and fungal communities.Soil organic matter,total nitrogen,available phosphorus and available potassium decreased by 4.17%～13.96%,3.07%～16.92%,6.43%～10.48% and 0.82%～2.33%,respectively.Degradable film residue increased soil organic matter,total nitrogen,available phosphorus and available potassium by 3.53%-16.05%,1.51%-12.30%,3.70%-7.84% and0.48%-1.77%,respectively.The residue of the two types of mulch reduced the p H value of soil by 1.98%～5.94%,and the non-degradable mulch decreased more under the same amount.Both types of residual mulch increased soil bulk density by 0.74%～10.37%,and nondegradable mulch increased more under the same residual amount.The residue of nondegradable film reduced the abundance and diversity of bacterial and fungal communities in soil.Biodegradable mulch residue increased the diversity of bacterial and fungal communities in soil.Degradable mulching film had better thermal insulation and moisture retention performance than non-degradable mulching film at the early stage of crop growth,and it also had a good performance in terms of yield yield.Both types of mulching film could cause soil surface microplastic pollution,but the microplastic abundance was lower after the use of degradable mulching film.At the same time,degradable residual film can increase the contents of organic matter,total nitrogen,available phosphorus and available potassium in soil,and improve the diversity of soil microbial community,while non-degradable residual film can reduce the above indexes.In conclusion,degradable mulching film has higher agricultural production benefits and lower environmental pollution pressure,and can replace nondegradable mulching film to become a more economical and environmentally friendly choice.