| Hetao irrigation area of Inner Mongolia is one of three large irrigation areas in China,is an important commodity grain production base,but Inner Mongolia hetao irrigation area soil due to more than 1000 ten thousand mu of arable land salinization is serious,in order to keep the influence of geographical environment,plastic film mulching technology has become an important agronomic measures of hetao irrigation area,of which more than 80%of the farmland use plastic film mulching on soil conservator,However,due to the imperfect recycling mechanism of agricultural film and long-term large-scale use,the content of microplastics in soil increases year by year.Soil microplastics may affect the health of farmland soil in Hetao irrigation area,leading to the gradual decrease of available agricultural land resources.Therefore,different types of microplastics were selected in this study to study the influence of microplastics on soil water infiltration and evaporation by indoor simulation experiment,and the influence of microplastics on water and salt migration of saline soil and soil physical and chemical properties was also studied in the experiment.Finally,the mechanism of microplastics on soil water migration was analyzed by(Computed Tomography)CT scanning technology.The results are as follows:(1)under the different type and abundance of micro plastic significant differences in soil water infiltration time,under the condition of the same type as the micro plastic abundance increase,cumulative infiltration time increased significantly,while different abundance of the same type of plastic occurrence conditions,in experimental PP group >PVC group > PE group > blank group cumulative infiltration time.(2)The maximum vertical water content of soil containing microplastics after onedimensional infiltration basically appeared at the depth of 10～25 cm,while CK in blank group appeared at the depth of 20～25 cm.The soil moisture content of the three types of microplastics increased with the increase of microplastic abundance at different soil depths.At the soil depth of 15 cm,the moisture content of PP microplastics with 0.5%,1.0% and2.0% abundance was 17.70%,18.50% and 19.23%,respectively.(3)At the same time,the migration distance and migration rate of the wet front decreased with the increase of microplastic abundance.When the infiltration time was60 min,the migration distance of the wet front in the PE,PVC and PP groups was 4.38%,8.76% and 10.58% lower than that in the CK group,respectively.7.30%,10.22%,14.60%and 10.95%,13.14%,15.33%,among which PP microplastics had the most significant effect.(4)The presence of microplastics inhibits the evaporation of soil water,and the cumulative evaporation of soil of the same type of microplastics decreases with the increase of the abundance.At 27 h of evaporation,the cumulative evaporation of soil column with the addition of 2% PP,PVC and PE microplastics decreases by 13.3%,19.4%and 22.9% compared with CK,respectively.The Rose evaporation model can reflect the change of soil evaporation over time with microplastics more accurately.(5)The soil moisture content in saline soil decreased with the increase of vertical direction,and the horizontal direction also decreased with the increase of the distance from the infiltration point source.After infiltration,the soil moisture content in the experimental group containing microplastics was higher than that in the blank experimental group in the same vertical and horizontal direction,and the soil moisture content increased with the increase of salt in the soil.The average water content of 7% saline soil increased to 9.35%and 11.2%,respectively,compared with that of 4% and 0.5% saline soil,and the average water content of 7% saline soil increased 13.65% and 14.24%,respectively,compared with that of 0.5% and 4% saline soil.(6)In the saline soil experiment,the salinity increased first and then decreased with drip irrigation infiltration in the vertical direction,and the same type of microplastics(PP)with the same abundance(2%)had a significant effect on the salinity of the saline soil after infiltration.In saline soil with different salinities,the experimental group with microplastics increased the soil salt content at sampling points compared with the experimental group without microplastics.(7)Occurrence of micro plastic with no occurrence of micro plastic saline soil experimental p H value in different horizontal distance decreases with the increase of the vertical direction,add micro plastic group in the same salt saline soil,vertical direction and horizontal direction were presented under the condition of p H value is greater than did not add the trend of the micro plastic group.(8)(Computed Tomography)CT scanning showed that the soil pore structure characteristics of the sample with 2% PP microplastics were significantly different from those of the blank sample(P<0.05).Two samples in the three dimensional scale soil pore number were increased with the increase of soil depth.The number of soil pore sizes is shown as: blank samples > add micro plastic PP samples,the other two different pore volumes increased with soil depth in blank sample is present linear increasing trend,while in micro plastic PP sample showed a power function growth trend.With the increase of soil depth,the difference between the total number of pores becomes larger and larger.At the same time,the pores in the blank sample are obviously sinking and have strong longitudinal continuity.However,the soil macropores prepared by PP microplastic have a high degree of fragmentation,and the overall pore distribution is chaotic.Compared with the blank sample,the pores are smaller,leading to smaller diameter of pore channels and non-aggregation.In conclusion,the occurrence of the microplastics in the soil increased the soil infiltration time,slow down the infiltration rate,the inhibition effect of soil water evaporation,and increase the moisture content of the soil in horizontal and vertical direction,increases the saline soil infiltration of sampling points in the process of salt content,and with the increase of micro plastic abundance trend is more obvious.Therefore,in the ecologically fragile farmland ecosystem,the gradual accumulation of microplastics will cause the deterioration of soil physical characteristics and affect the distribution of salt in saline soil,which is not conducive to the sustainable development of agriculture,and should be enough to cause our attention. |
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