Current Situation Of Residual Mulch Film And Its Effect On Physicochemical Properties Of Farmland Soil In Hunan Province

Mulch film is widely used in agricultural practice to achieve high water use efficiency,high crop yield,early harvest and improve crop quality.Chinese farmland consumes a lot of mulch film,most of which are not recovered in time after crop harvest,resulting in the continuous accumulation of residual mulch film in farmland.In the past,the research on the distribution and characteristics of residual film pollution was mainly concentrated in Xinjiang,Gansu and other northern regions with large use of mulch film,but in recent years,there have been related reports of residual film pollution in some southern provinces,but the scope of the study is not large.more comprehensive and in-depth research is needed.Therefore,this study searched the data of the use of farmland film in the past three years（2017-2019）in China,and investigated the use and recovery of mulch film in farmland soil in various counties and cities of Hunan Province.in addition,a questionnaire survey was conducted on the use of mulch film by local residents,the main controlling factors affecting the distribution trend of residual mulch film were analyzed,and the morphological characteristics of mulch film in different soil layers were revealed.The effects of residual mulch film on soil physicochemical properties were discussed,which provided data and theoretical support for the prevention and control of residual mulch film in farmland soil in Hunan Province.The main conclusions are as follows:（1）The data retrieval report from 2017 to 2019 shows that the usage amount of agricultural film,mulch film and total film coverage area have been decreasing year by year for three consecutive years.The usage amount of agricultural film and mulch film in most areas of Hunan province has been decreasing year by year for three consecutive years,however,the total coverage area of mulch film has been increasing year by year.Further analysis through the questionnaire survey showed that the film mulching amount,planting crops and annual precipitation had a great influence on the abundance of residual mulch film.The results showed that the abundance of residual mulch film in cultivated soil was significantly affected by natural environment and man-made.（2）The results of distribution,morphological characteristics and mulch type identification of mulch film residues in cultivated soil showed that there were significant differences in the abundance of residual mulch film in different soil sampling sites in Hunan Province.The total abundance of residual mulch film in cultivated soil of all sampling sites in Hunan province were 5416.67±312.19 particles kg^-1.The distribution of residual mulch film in these areas is mainly concentrated in0～20cm soil layer（70%）.The morphology features of residual mulch film in cultivated soil are mainly transparent（56.31%）and flaky（81.85%）,and the particle size is smaller than 5mm（66.00%）.Among the representative residual mulch film,the plastic types of PP,nylon and PE accounted for 44.45%,33.33%,and 22.22%respectively.The amount of the total mulch film amount,annual precipitation,and planting pattern are the main controlling factors of mulch film residue in cultivated land.（3）The results of the effect of residual mulch film on soil properties showed that the long-term existence of residual mulch film in cultivated soil could change the soil nutrient content,in which the soil bulk density decreased significantly,the soil water content increased significantly,and the soil hydraulic conductivity of each monitoring site decreased significantly,film mulching could increase the content and porosity of1-2mm mechanical aggregates in cultivated soil,and the soil nutrient index,organic matter content and p H value in the residual area of mulch film showed a downward trend.The long-term existence of mulch film residues in cultivated soil will lead to the accumulation of NO₃^--N in the soil,which is more conducive to the transformation of NH₄⁺-N to NO₃^--N.The soil residue volume was significantly positively correlated with soil water content and negatively correlated with soil capacity,water conductance,total N,P,K and available K contents.However,no significant correlations were found among all levels of aggregates,porosity,organic matter,alkaline nitrogen,NH₄⁺-N,NO₃^--N,available P contents and pH of the soils.