Characteristics And Ecological Effects Of Soil Microplastics Distribution Under Different Mulching Years In Manas River Cotton Region

Plastic film mulching is widely used in farmland.The use of plastic film is large and the residue is also very serious.The pollution problem caused to farmland is becoming more and more serious.Plastic film mulching is the direct source of soil micro plastics.Micro plastics have strong adsorption.Once they enter the soil,they will widely exist in the soil,causing potential harm to soil biological community,agricultural production and human health.Cotton is one of the main cash crops in Xinjiang and one of the main sources of increasing people’s income.Due to the long-term use of plastic film and the untimely recovery of plastic film,a large amount of residual film has accumulated in the cotton field,resulting in serious plastic film pollution,changing the physical and chemical properties of soil,resulting in the decline of cotton quality and yield,and hindering the sustainable development of cotton industry in Xinjiang.Therefore,it is of great guiding significance to explore the distribution characteristics and ecological effects of soil micro plastics under different film mulching years in Manas River cotton area,and put forward corresponding solutions to control soil micro plastic pollution at the source and control system.Taking the Manas River cotton area as the study area,the soil of Manas River cotton field was investigated and sampled in April and October 2021 by collecting soil samples under different film mulching years（0,5,10,20 and 30 years）and different soil depths（0-10,10-20 and 20-30cm）,the abundance,color,type,particle size and surface morphology of micro plastics were analyzed,and the physical and chemical properties of soil were determined Soil enzyme activity,soil microbial biomass carbon,nitrogen,soil aggregate and cotton yield were used to explore the distribution characteristics and ecological effects of soil micro plastics under different film mulching years in Manas River cotton area.The main research results show that:（1）The abundance of micro plastics in the soil of Manas River cotton field ranges from 1565.94 to3560.66 pieces·kg^-1,and the abundance of micro plastics increases with the increase of film mulching years,and the difference is significant（P<0.05）.The abundance of micro plastics decreases with the deepening of soil depth.The main types of soil micro plastics in Manas River cotton field are film,fragment,fiber and foam,accounting for 16.81%,24.69%,47.39%and 11.11%respectively;The colors of micro plastics include white,transparent,black,yellow and other colors,accounting for 69.02%,14.78%,6.49%and9.71%respectively;The particle size of microplastics decreases with the increase of film covering years,and the percentage of microplastics with particle size less than 0.5mm is the largest.In the distribution characteristics of soil micro plastic color abundance in Manas River cotton field,the abundance of white transparent micro plastic is the highest;In the distribution characteristics of type abundance,the abundance of fiber,fragment,film and foamed micro plastics decreased in turn;In the distribution characteristics of particle size abundance,the abundance of microplastics with particle size<0.5mm is significantly higher than that of the other three particle sizes,accounting for more than 50%.The surface of the micro plastic sample is rough and irregular,with obvious cracks and many pores.At the same time,the surface cracks are mixed with impurities such as soil particles,with a high degree of weathering.（2）With the increase of film mulching years,the soil water content and organic matter content gradually increased,and the highest was 11.52%and 21.60 g·kg^-1respectively in 30 years.The soil bulk density and soil available phosphorus increased first and then decreased.The highest content was 1.40g·cm^-3and 49.60 mg·kg^-1respectively in 10 years.The soil electrical conductivity,available potassium and alkali hydrolyzable nitrogen generally decreased;Under the same film mulching years,with the increase of soil depth,soil water content and conductivity gradually increased,p H value,organic matter,available phosphorus,available potassium and alkali hydrolyzable nitrogen gradually decreased,and soil water content and bulk density did not change significantly.Under different film mulching years,soil sucrase,urease and alkaline phosphatase increased first and then decreased with the increase of film mulching years.The content was the highest in 10 years of film mulching,which were 10.57 mg·g^-1·d^-1,0.86 mg·g^-1·d^-1and0.4 mg·g^-1·d^-1respectively,and the range of soil catalase was 1.80-2.20 ml·g^-1.With the increase of micro plastic content,the soil microbial biomass carbon content increased first and then decreased,up to 205.26mg·kg^-1.The microbial biomass nitrogen content gradually decreased,and the soil microbial biomass carbon and nitrogen were higher in the surface layer than in the deep layer.（3）With the increase of film covering years,the proportion of small particle size aggregates gradually increases,and the proportion of soil quality of 0.25-0.053 mm in each particle size of soil aggregates is higher,accounting for 48.77%of each particle size.The percentage of soil aggregate particle size of 2 mm decreases with the increase of film covering years,the percentage of soil aggregate particle size of 2-0.25mm has no significant change,the percentage of soil aggregate particle size of 0.25-0.053 mm increases year by year,and the percentage of soil aggregate particle size of<0.053mm shows irregular change.（4）The yield of cotton covered with plastic film for 5 years,10 years,20 years and 30 years was 6765.37kg·hm^-2,6709.15 kg·hm^-2,6203.15 kg·hm^-2and 6071.96 kg·hm^-2,this indicated that continuous plastic film mulching for 30 years had no significant effect on cotton yield.