| The application of plastic film mulching technology in agriculture can reduce the impact of climate on crop growth to a certain extent.However,with the continuous increase of long-term plastic film mulching drip irrigation and plastic film planting investment,the residual film pollution in cotton field is becoming more and more serious.On the one hand,the plastic film is mainly composed of high polymer,which is difficult to decompose and can remain in the soil for hundreds of years;On the other hand,not only the popularization rate and recovery rate of residual film recovery machinery are low,but also farmers use a lot of plastic film during planting,but the recovery is relatively small,resulting in a large number of plastic film fragments in the soil for a long time,which has a negative effect on the soil and crops.In order to explore the effects of different amount of residual film on soil physical properties and cotton growth,through the combination of indoor soil column,soil water characteristic curve test and field test,this study set up seven kinds of residual film content treatments without residual film control group:0(CK),150(T1),230(T2),465(T3),857(T4),1250(T5)and 1640(T6)kg/hm~2,and deeply studied the effects of different amount of residual film on soil water vertical infiltration The physical characteristics such as soil water holding characteristics and their impact on the growth and development of cotton put forward the basis for the agronomic management methods in the area polluted by residual film.The main conclusions include:(1)With the increase of the amount of residual film,the soil permeability and water holding capacity decreased gradually,and the time-consuming of water infiltration to 40 cm soil layer increased(P<0.01).The migration time of T6 treatment increased by 71.88%and the water infiltration rate decreased by 56.63%compared with CK treatment;Kostiakov model is suitable for simulating the movement process of wetting front of soil with residual film,and the determination coefficient R~2 is greater than 0.92.Under the condition of high negative pressure(>100 k Pa),when the suction is 100～1500 k Pa,the average moisture content of T6 treatment is 83.36%of that of membrane free treatment.The difference increases with the increase of suction.The fitting degree of VG model to the soil moisture characteristic curve of different residual film amount soil is good.The maximum sum of stagger squares of each treatment is 3.17e-05,the maximum value of RMSE is 0.00359,and the minimum determination coefficient R2 is 0.99786.(2)With the increase of the amount of residual film,the soil bulk density gradually increased,and the soil porosity,water content and total nitrogen content of cotton roots gradually decreased.Compared with CK without residual film,the soil bulk density of T6 treatment increased by 4.40%,and the soil porosity decreased by 5.51%.The residual film enhanced the enrichment effect of soil salt in 0-40 cm soil layer.The average salt content ratio of 0-40 cm and 0-80 cm in T6 treatment increased by 18.65%.The residual film also affected the balance of soil water and salt distribution.The variation degree of soil water and salt was positively correlated with the residual film content.The soil water and salt variation coefficient CV of T5and T6 treatment was significantly larger,with water CV of 0.52 and 0.44 and salt CV of 0.34 and 0.31respectively.(3)The plant height,stem diameter,leaf area index and biomass decreased with the increase of residual film.The plant height,stem diameter and leaf area index of cotton in the study area can be fitted by logistic growth model.The theoretical maximum values of plant height,stem diameter and leaf area index of T6treatment decreased by 24.87%,9.60%and 26.26%respectively compared with no residual film treatment;The biomass decreased by 27.34%,and the residual film inhibited the development of cotton vegetative organs and reproductive organs.The proportion of dry weight of cotton reproductive organs in the whole plant gradually decreased with the increase of residual film content,which was not conducive to the formation of cotton yield.(4)With the increase of the amount of residual film,the number of bolls per plant,boll weight,seed cotton yield,irrigation water use efficiency IWUE and harvest index hi decreased;Compared with no residual film treatment,the number of bolls per plant of T6 decreased by 20.48%,the weight of single boll decreased by 24.56%,and the IWUE decreased by 18.75%,HI decreased by an average of 13.8%.The cotton yield decreased gradually.When the residual film content was greater than 230 kg/hm~2,the decline was significantly enhanced.The yields of T3,T4,T5 and T6 decreased by 14.19%,21.69%,29.19%and 37.29%respectively compared with no residual film treatment.(5)The residual film content was positively correlated with the coefficient of variation of soil water and salt in 0-40 cm of cotton at flowering and Bolling stage,and negatively correlated with soil water content and cotton growth index.The growth indexes of cotton in the study area are positively correlated,and the salinity of 0-40 cm soil layer is negatively correlated with each growth index. |
