Effects Of Residual Plastic Film Accumulation On Cotton Growth And Soil Water Movement Under Long-Term Mulched Drip Irrigation

Object:With the rapid development of drip irrigation technology under mulch,it has greatly promoted the rapid development of agricultural economy.At present,Xinjiang’s cotton planting area and the amount of mulch film used are the first in the country,but the problem of residual mulch film in cotton soil caused by drip irrigation under mulch has become a serious obstacle to the sustainable development of drip irrigation under mulch technology.The management and research of the residual soil film in cotton fields under long-term drip irrigation has become a hot issue at present.This paper analyzes the effects of long-term drip irrigation cotton fields with different residual film accumulations on cotton physiological growth,yield and water use efficiency,cotton root morphological parameters and distribution characteristics,soil water and salt movement and nutrients in cotton fields to reveal the different residual film accumulations.The growth and development of cotton and its influence on cotton field soil provide theoretical support for the research on the harm of residual film pollution in long-term mulched cotton fields in Xinjiang and the recovery and treatment of residual film on farmland soil.Methods:Based on barrel experiment and field experiment,"Xinluzao 23"was used as the test cotton variety.According to the characteristics of residual film accumulation in Oasis mulched drip irrigation cotton field,6 different residual film accumulation treatments and 1 control group without residual film treatment were set up,with a total of 7 treatments,and each treatment was set with 3 replicates.In addition,samples were collected from 6 cotton fields of No.6 company of No.121 regiment in Shihezi city.Results:（1）The residual film in the cotton field has a significant impact on the growth and development of cotton.At different growth periods of cotton,under the hindrance of the residual film in the soil,the cotton plant height,stem thickness and leaf area index gradually decrease with the increase of the accumulation of residual film.When the drip irrigation period of film mulching is less than 20 years,the accumulation of residual film has no significant effect on the plant height,stem thickness and leaf area index of cotton.As the drip irrigation period of film mulching increases,the amount of residual film exceeds 391.73 kg·hm^-2（film mulching 20 a）The plant height,stem diameter and leaf area index of cotton began to decrease significantly.In the early stage of cotton growth and development,the stress effect of residual film was small,while the stress effect of residual film became stronger during the bud and boll stage of cotton growth,and the differences between the treatments were significant.（2）The SPAD content of cotton leaves treated with residual film decreased significantly,and the SPAD content of cotton leaves at bud stage and flowering and boll stage were as follows:CK>T1>T2>T3>T4>T5>T6.The accumulation of residual film in the cotton field has a significant effect on the photosynthetic characteristics of cotton.With the increase of the accumulation of residual film,all the photosynthetic characteristics of cotton gradually decrease.When drip irrigation with film mulching for15 years,during the same observation period of different growth periods of cotton,cotton leaf P_n bud stage decreased by up to 5.30%,T_r flocculation stage decreased by up to 15.06%,G_s flowering and boll stage decreased by up to 54.13%,and C_i bud stage decreased by up to 23.58%.（3）With the increase of soil residual film accumulation in cotton field,the dry weight of aboveground part and root system decreased gradually at the end of growth period.Under the treatment of no residual film,the aboveground dry weight and root dry weight of cotton were the largest,the greater the accumulation of residual film,the more obvious the decrease of aboveground dry weight and root dry weight,and the corresponding root shoot ratio was also significantly reduced;the root dry weight decreased by 38.86%and 35.40%,and the aboveground dry weight decreased by 23.31%and 21.12%under the treatment of maximum residual film content in two years.Compared with no residual film treatment,the boll number per plant and boll weight per plant of residual film treatment were significantly reduced,resulting in the decrease of cotton yield of residual film treatment.There was a negative correlation between cotton yield and soil residual film amount.When the residual film amount was more than 309.88kg·hm^-2（film mulching 15 a）,the boll number per plant,boll weight per plant,yield and water use efficiency of cotton decreased significantly.The correlation between yield and growth indexes and yield components was significant,which indicated that the process of cotton affected by residual film was the result of multiple factors.（4）The residual plastic film in farmland soil affected the growth and spatial distribution of cotton roots in the tillage layer.The results showed that the root length density,root surface area density,root volume and root diameter of cotton roots were negatively correlated with the amount of soil residual film,and the root morphological parameters of each residual film treatment were lower than those of no residual film treatment.Root length density,root surface area density,root volume and root diameter decreased by36.6%,23.2%,13.3%and 32.2%,respectively.The spatial distribution of cotton roots in 0～40 cm of tillage layer was significantly affected by residual film.From the distribution of root length density and root surface area in each soil layer,the effect of residual film on cotton roots was concentrated in 10～30 cm soil layer with more residual film.（5）The residual film in soil leads to the change of soil bulk density and porosity.With the increase of residual film amount,soil bulk density increased,and soil porosity varied in different soil layers.The change of soil physical properties affected the distribution of soil water and salt.The existence of residual film reduced soil water content,water distribution uniformity and water holding capacity,and salt accumulation occurred in some soil layers.At the same time,soil nutrient content changed significantly with the increase of residual film.Conclusions:Long-term mulched drip irrigation had significant effects on cotton growth,soil moisture and salinity.Under the experimental conditions,mulching drip irrigation for 15～20 years(the amount of residual film was 309.88～391.73 kg·hm^-2)had a significant effect on soil residual film pollution,and the growth characteristics,photosynthetic characteristics,yield and water use efficiency of cotton were significantly lower than those of no residual film treatment,With the increase of film mulching years,the accumulation of residual film increased,resulting in the changes of soil bulk density and porosity,and the decrease of soil water and salt distribution uniformity and soil nutrients.The dry weight of shoot and root decreased by 20.3%and 38.4%respectively,and the yield decreased by 10.96%compared with the average yield per unit area in recent five years.Based on the above analysis,for cotton fields with long-term film mulching and drip irrigation years of 15～20 years,we should increase the recovery of residual film and promote the use of degradable plastic film,so as to ensure the sustainable development of cotton fields with long-term film mulching and drip irrigation.