Effects Of Mulching Film Of Different Types On Soil Environment Of Farmland In Mountainous Area Of Southern Ningxia

As a means of increasing soil temperature and retaining soil moisture,plastic film mulching plays an important role in agricultural production.The mulching technology effectively improved the moisture and temperature of the soil plough layer,which provides an important guarantee for promoting crop production and income and achieving national food security.For a long time,with extensive use of plastic film,its disadvantages of being difficult to degrade and recycle has resulted in massive residues of plastic film in soil,which not only damaged the soil structure,but also caused serious environmental problems（i.e.,"white pollution"）,ultimately threaten the soil health and sustainable development.The degradable plastic film can be rapidly degraded into CO₂ and H₂O under natural conditions,and effectively alleviate the soil environmental pollution.However,the degradable plastic film is easily affected by environmental factors such as light and rainfall,and has different effects on the soil environment under different climatic conditions.The mountainous area of south Ningxia has a typical continental monsoon climate.Plastic film is widely used in agricultural production practice due to the limitation of drought and low temperature climate conditions,but the effect of degraded plastic film on soil ecological environment in this area is still unclear.In view of the above scientific problems and technical requirements,this study took the soil without mulching as the control（CK）,and selected 2 different types of ordinary polyethylene mulch films（white film,marked as W;black film,marked as B）and 3 different types of biodegradable mulch films（PE,PB and PP）as mulching materials to analyze the effects of different plastic film mulching on soil moisture and temperature,soil organic carbon and nitrogen content,soil enzyme activity and soil bacterial community under the condition of no crops.The main conclusions are as follows:（1）Under the condition of no rainfall replenishment,compared with no-film mulching,the mulching treatments inhibited the loss of soil moisture,and the ordinary mulching film was more effectively than degradable mulching film on increasing soil moisture.Under the condition of rainfall replenishment,light-rain and moderate-rain events had no significant effects on soil moisture content under ordinary and degraded plastic films.After the heavy rain events,all the mulching treatments significantly increased soil moisture content.Due to the damage of the film at the latter of the experiment,there were no significant differences between PB\PP and no-film mulching in soil moisture content,whiles the soil moisture of ordinary films（W and B）treatments has a clearly lower replenishment than that of no-film mulching and degradable films treatments.（2）There is a positive correlation between soil temperature and air temperature under the mulching treatments.For every 1°C increase in air temperature,the soil temperature of CK,W,B,PE,PB and PP increased by 0.98℃,1.15℃,1.03℃,1.11℃,0.64℃and 0.59℃,respectively.With the damaging of degradation film（PB and PP）,the heating rate of soil temperature was no different from that without film.Plastic film mulching significantly increased the total effective accumulated temperature of soil,and the warming effect of ordinary plastic film is higher than that of degraded plastic film.The soil total effective accumulated temperature followed the order of W>PE>B>PB>PP>CK.The effective accumulated temperature of the degradable film（PB and PP）was significantly higher than that of no-film mulching before the degradable film was damaged,but no difference with no-film mulching after it was damaged.Among them,the soil effective accumulated temperature of PE was lower than that of the ordinary films（W and B）but significantly higher than that of the degradation films（PB and PP）.（3）Film mulching significantly changed the microbial biomass carbon and nitrogen content in the 0-10 cm soil layer,and the changes of soil microbial biomass carbon and nitrogen under different mulching films were significantly different.Compared with no-film mulching,the soil microbial biomass carbon of ordinary film W and degradable film PE decreased by 27.40%and 24.53%,respectively,and the soil microbial biomass carbon of ordinary film B,degradable membrane PB and PP increased by 42.55%,132.93%and15.24%,respectively;the soil microbial biomass nitrogen of ordinary membrane W and degradable film PP increased by 117.70%and 115.40%,respectively,and the soil microbial biomass carbon of degradation film PE decreased by 35.21%.There was no significant difference between B\PB and CK.（4）There were significant differences in soil invertase and urease activities under different mulching films.Overall,compared with CK,all mulching treatments reduced the soil invertase activity.The urease activity of the degraded film（PB and PP）treatments was higher than that of the ordinary film（W and B）treatments.Film mulching reduced soil organic carbon content,and the organic carbon content under different film mulching treatments showed the order of CK>ordinary film（W and B）>degraded film（PB and PP）,indicating that the reduction of soil organic carbon by degraded film（PE,PB,and PP）was higher than that of ordinary film（W and B）.Compared with CK,ordinary film W significantly increased soil total nitrogen content,and there were no significant differences between the ordinary film B or degradable films（PE,PB,and PP）and CK.（5）Film mulching changed the composition of soil bacterial community.Compared with CK,W,B,and PB treatments reduced the OTUs（Operational taxonomic units）of soil bacteria,and PE and PP treatments increased the OTUs of soil bacteria.The diversity of bacteria in different membrane treatments was PP>PE>CK>B>W>PB;the abundance was B>W>PP>PE>CK>PB.The soil bacterial diversity of degradable film treatments was higher than that of ordinary plastic film treatments.The Proteobacteria,Actinobacteria and Firmicutes were the main components of soil bacteria,and the relative abundance of these bacterial in degradable film treatments were higher than that in ordinary film treatments.The dominant flora at the genus level were mainly bacterial genera that existed in the soil environment but could not be cultivated.Overall,mulching increased soil temperature and inhibited soil moisture evaporation.Compared with no-film,the water retention performance and temperature increase effect of degradable plastic film are lower than that of ordinary plastic film,and there is no difference between it and no film after degradable plastic film damaged.Different types of plastic film mulching had different effects on soil microbial biomass carbon and nitrogen,reducing soil organic carbon total nitrogen content and enzyme activity.Degradable film mulching increased soil bacterial community composition and improved soil environment.