Study On The Migration Law Of Microplastics In Different Texture Soils Based On Drip Irrigation

【Objective】As a new type of soil persistent pollutant,microplastics have a serious impact on soil environment and crop health,and have become a research hotspot at home and abroad.Revealing the law of drip irrigation amount on the migration and distribution of microplastics in different farmland soil textures can provide a theoretical basis for the treatment of microplastics in large-scale film-covered irrigation areas in China,and has important guiding significance for the prevention and control of microplastic pollution in farmland soil.【Method】In this study,sandy soil and loam soil were used as the object,and the agricultural drip irrigation activities were simulated by indoor soil column in-situ test.Four drip irrigation treatments of CK（0 L）,T1（28.26 L）,T2（56.52 L）and T3（84.78 L）were set up,and the frequency of drip irrigation was once every3 days.The conventional drip irrigation amounts of 0,2,4 and 6 years in the field were simulated respectively.Five kinds of polyethylene microplastic particles with different particle sizes（<50μm,50～200μm,200～350μm,350～750μm,750～1250μm）were used as materials to make soil-microplastic mixed surface layer.The effects of different drip irrigation amount and microplastic particle size on the vertical migration of microplastics in soil were investigated.【Results】1.Drip irrigation accelerated the migration and accumulation of microplastic particles in surface soil,and the abundance and migration depth of microplastics increased with the increase of drip irrigation amount.In sandy soil,the total cumulative migration of microplastics under T1,T2 and T3 treatments were 19733.33,35666.67 and 52200.00 pieces·kg^-1,respectively.In loam soil,the total cumulative migration of microplastics under T1,T2 and T3 treatments were 12000.00,16300.00 and 24266.67 pieces·kg^-1,respectively.The migration depth of microplastics in sandy soil and loam soil reached the highest when the drip irrigation amount（T3=84.78L）was simulated in the field for 6 years,while the microplastics in the non-drip irrigation treatment remained in the 0～5 cm of the soil surface.The amount of drip irrigation was positively correlated with the abundance and depth of microplastics（P<0.05）.The accumulation of microplastics in sandy soil was higher,but the migration depth of microplastics in loam soil was deeper.2.All 5 kinds of microplastics can migrate through soil leaching,and the soil texture has particle size selectivity for microplastics migration.In sandy soil,smaller particle sizes（<50μm,50～200μm）Has significant migration ability,accounting for 90%to 93%of the total migration amount;In loam soil,200～350μm,350～750μm.The migration ability of m particle size is relatively high,accounting for 49%～69%of the total amount.At the same time,the migration rate of microplastics is also different in different soil textures has the fastest migration rate,ranging from 200 to 350 in loam soil.The migration rate of m is the fastest.By establishing the migration fitting equation between irrigation amount and microplastics abundance and depth in different soil textures,it was found that there was an obvious linear relationship between irrigation amount and microplastics abundance and depth.In each particle size group,the microplastics abundance R²>0.66,depth R²>0.61,and the fitting effect is good.3.The amount of drip irrigation,soil moisture content and porosity are the main factors affecting the abundance and depth of microplastics.Random forest regression（RFR）analysis showed that drip irrigation amount,soil water content and porosity were important factors affecting the change of microplastics.Further variance decomposition analysis showed that the three together explained 63.81%of the change.In addition,there were differences in the effects of different texture soils.In sandy soil,drip irrigation amount and soil physical and chemical properties had obvious effects on the change of microplastic migration particle size,and the contribution rate was 92.2%.In loam,drip irrigation amount and soil physical and chemical properties had obvious effects on the abundance and depth of microplastics,which were 79.2%and 91.6%,respectively.【Conclusion】By studying the distribution characteristics of soil microplastics in 0～50 cm soil layer under different drip irrigation amounts,the differences and laws of microplastic migration between sandy soil and loam were clarified,and the main soil factors affecting the change of microplastics were determined.The fitting relationship between drip irrigation amount and microplastic migration depth established in this study showed that microplastics in sandy soil and loam tillage layer（0-30 cm）could migrate to 1 m soil layer under drip irrigation amount of 9.34 and 6.56 years,respectively.Drip irrigation activities accelerate the migration and diffusion of soil microplastics and may lead to secondary pollution of microplastics.