Legacy Effect Of Plastic Film Mulching And Nitrogen Application On Soil And Crop

Plastic film mulching（PFM）and nitrogen（N）fertilization are widely used global agricultural management practices.While they bring huge economic benefits,also bring serious ecological and environmental problems.Crop yield and high biomass harvesting under long-term mulching may cause soil nutrient depletion,and residues of large amounts of mulching may affect soil structure and thus may have negative legacy effects on crop growth.Long-term application of urea nitrogen can lead to soil acidification,and continuous soil acidification may have an impact on soil nutrient availability,especially phosphorus（P）availability,but it is unclear whether it will cause crop phosphorus limitation.Therefore,this study was based on the long-term plastic film mulching and fertilization experimental station of Shenyang Agricultural University（established in 1987）,two experiments were carried out with four treatments of plastic film mulching combined with nitrogen application(135 kg N ha^-1 yr^-1),plastic film mulching without nitrogen application,no mulching combined with nitrogen application and no mulching without nitrogen application.The goal of experiment 1 was to evaluate the effects of long-term plastic film mulching and nitrogen fertilization on soil and plant nutrients.The goal of experiment 2 was to explore the changes of soil physical and chemical properties and plant growth and development after long-term plastic film mulching stopping.Finally,the legacy effects of long-term mulching and nitrogen application on soil and plants were revealed.The main findings are as follows:（1）Soil nutrients and p H.Long-term mulching increased the concentrations of,total Ca,total Mn and total Cu in the topsoil,but had little effect on soil nutrient availability,only affected the concentrations of exchangeable Ca and DTPA-Fe in the 20-40 cm soil layer.Long-term nitrogen fertilization decreased soil concentrations of Olsen-P,exchangeable Ca,exchangeable Mg and DTPA-Zn,indicating that long-term nitrogen fertilization caused soil nutrient deficiency to a certain extent.Long-term nitrogen fertilization decreased soil p H,increased soil alkali-hydrolyzable nitrogen,DTPA-Fe and DTPA-Mn concentrations.There was a significant correlation between extractive nutrient contents and soil p H,implying that the decreases of soil nutrients and p H were legacy effects of long-term plastic mulching film and nitrogen fertilization.（2）Plant nutrients.Long-term plastic film mulching increased the concentrations of P in stems and leaves and decreased the concentrations of N,K,Ca,Mg,Mn and Zn.On the contrary,N fertilization increased N,K,Ca,Mg,Mn,Cu,and Zn concentrations and decreased the P concentration.In vegetative organs（i.e.,stems and leaves）,most nutrient concentrations showed opposite responses to N fertilization and mulching.There was no such regularity in the responses of most nutrients in seeds to N fertilization and mulching,but had a tendency to decline.（3）Soil physical and chemical properties.The soil NO₃^--N in the long-term N fertilization plot was much higher than that at no fertilized plot,and lower P supply capacity of soil at the early stage than that at no fertilized plot.Compared to never mulching,the surface layer of previous mulching treatments had higher soil compactness,larger bulk density and lower porosity,which promoted the maintenance of soil moisture.（4）Crop growth.After the long-term mulching plots stopped mulching,the biomass,stem thick,plant height,and total root length of maize at seedling stage were higher than those in the never mulching plots,and the maturity time of maize was 6～10 days earlier than that in the never mulching treatment.which was related to the increase of soil moisture in the film mulching plot.However,there was no difference in the yield between the previous mulching plots and never mulching plots.The long-term N fertilization plot showed strong phosphorus deficiency symptoms at the seedling stage,reduced biomass,stem thick and plant height,thus causing the maturity of maize moved forward for 10～15 days.However,there was little difference in maize growth in later stage compared with no nitrogen application treatment,and the biomass and yield in mature stage were similar to that in no nitrogen application treatment.To sum up,long-term plastic film mulching has little impact on the change of soil nutrients.Although long-term mulching could produce plastic residues,it had little negative impact on maize growth.Long term nitrogen application caused soil nutrient deficiency to a certain extent.Long-term nitrogen fertilization could cause phosphorus deficiency symptoms in the seedling stage of crops,which was a negative effect on maize growth.