Effects Of Plastic Film Residues On Soil Physicochemical Properties And Maize Productivity In Dryland

With the dramatic increase using of agricultural plastic film,the potential environmental risks associated with it are receiving widespread attention.Biodegradable film（BF）is considered an alternative to conventional polyethylene film（PF）.However,the promotion and application of BF is at an early stage,and it is debatable whether it will raise similar ecological risks as PF.Therefore,a field experiment was conducted across two spring maize growing seasons in the Loess Plateau region of China.Aimed to investigate the effects of the residual BF（polylactic acid,PLA）and PF（RBF and RPF）on soil physicochemical properties and maize productivity in dryland at three residual levels:75 kg·ha^-1,150 kg·ha^-1,and 300 kg·ha^-1.No residual film（NRF）was used as control.The experiment aims to provide theoretical references for the restoration and protection of the soil environment in long-term film-mulching areas and areas with serious residual film pollution,the formulation of crop farming,irrigation,and fertilization systems.Further to boost the rational promotion and application of BF and the healthy development of the industry,to ensure the agricultural clean production in China.The main conclusions of this experiment are as follows:（1）Agricultural film residues changed the soil physical structure in dryland.With increasing residual levels,soil bulk density and compactness increased,porosity decreased,and the proportion of large soil water-stable aggregates（>0.25 mm）decreased.Soil bulk density and compactness in RPF₃₀₀were on average 5.11%and 7.78%higher and porosity was on average 5.49%lower than NRF.The changes in the soil physical structure caused spatial-temporal differences in soil hydrothermal properties.The differences between treatments existed mainly at the maize jointing and filling stages.Soil water content（SWC）in the 0-40 cm soil layer decreasing with increasing residual levels,and soil temperature at10 cm increasing.Compared to the NRF,nitrate and ammonium nitrogen contents all increased in the 0-40 cm soil layer of the residual film treatment.（2）Both aboveground agronomic traits and root characteristic parameters of maize were significantly reduced with increasing residual levels.However,the aboveground parts and the roots of maize to the film residues were different in terms of sensitivity period.The root was more sensitive to residual film at the nutritional growth stage,with the greatest difference in root length density and surface area density between the residual film treatments and NRF at the jointing stage.While the aboveground was more sensitive to residual film at the reproductive growth stage,with the greatest difference in green leaf area and leaf area index between the residual film treatments and NRF at the filling stage.Increasing with residual levels from jointing to tasseling,and decreasing with residual levels at physiological maturity.（3）Agricultural film residues in the 0-20 cm soil layer negatively affected spring maize productivity and resource use efficiency in dryland.In the jointing stage,the root-shoot ratio（RSR）decreased with increasing residual levels,which was detrimental to early root establishment.In the filling stage,RSR increased with increasing residual levels,detrimental to maize dry matter accumulation and yield formation in the aboveground.Grain yield,water use efficiency（WUE）,precipitation use efficiency（PUE）and nitrogen partial factor productivity（NPFP）of maize were significantly reduced under residual film treatment.（4）After two spring maize growing seasons,RBF degraded incompletely,but the degradation rate was much higher than that of RPF.59.24%of RBF was degraded during the experiment period,while the degradation rate of RPF was only 0.69%.Regardless of the type of residual film,soil physicochemical properties,maize agronomic traits,yield and resource use efficiency were significantly reduced when the residual level was≥150 kg·ha^-1.150 kg·ha^-1may be the threshold for residual film to negatively affect maize growth and development.RBF also has a greater negative impact on maize productivity when it is not degraded below the threshold.After one year degradation period,the effects of RBF treatment on soil physicochemical properties and maize production were significantly reduced during the second spring maize growing season.Soil water content,nitrate nitrogen content and ammonium nitrogen content in the 0-40 cm soil layer were 3.70%higher,7.43%and 10.00%lower,respectively,for RBF₃₀₀than for RPF₃₀₀.Compared with RPF treatments,the grain yield and water use efficiency of RBF treatments increased by 0.41%-6.24%and0.12%-4.44%,respectively.In conclusion,BF mitigates the effects of residues on soil physicochemical properties and maize productivity in dryland.It is an alternative to PF,but it is still necessary to recycle residual film as much as possible.