| Plastic film covering is the core technology for stabilizing and improving crop yield in dryland farmland on the Loess Plateau.However,the long-term use of plastic film mulching,coupled with incomplete recovery of residual film,has led to a large number of residues of film fragments and micro plastics in farmland soil in this area,which is not only detrimental to the maintenance of soil health,but also poses serious threats and challenges to the long-term protection of crop production capacity and food security in this area.However,it is currently unclear how microplastic residues affect the physical and chemical properties of farmland soil,carbon and nitrogen dynamics,and crop nitrogen utilization patterns.This study was conducted in two maize growing seasons,2021 and 2022,using a micro region large region nested method.Powdered polyethylene microplastics(with a particle size of about 150 um and a concentration of 30 g m-2)were added to the micro region,while microplastics were not added to the large region.At the same time,three nitrogen fertilizer application levels(N1:240 kg ha-1,N2:180 kg ha-1,N3:120 kg ha-1)were set up to systematically analyze the effects of nitrogen application levels and microplastics addition on soil physical and chemical properties,soil carbon and nitrogen dynamics The impact of nitrogen utilization and yield formation in maize.In order to clarify the production and ecological effects of microplastic residues,and provide a theoretical basis for the sustainable development evaluation of film covered agriculture in this area.The main research findings are as follows:(1)Compared with the absence of microplastics,microplastics increased the soil moisture content of 0-100 cm during the jointing stage of two maize seasons under high and medium nitrogen levels,increased by 4.48% in the previous season under high nitrogen levels,and increased by 10.84% in the latter season under medium nitrogen levels;Microplastics have an impact on the soil moisture content during the tasseling period of the previous season of corn.Under high and medium nitrogen levels,the soil moisture content decreased by 4.31% and 5.05%,respectively,and increased by 17.43% under low nitrogen levels;Under moderate nitrogen levels,microplastics have a significant impact on soil moisture content during the corn harvest period.The previous season increased the moisture content of each soil layer,while the following season decreased the moisture content of each layer.(2)Compared with the absence of microplastics,microplastics showed a decrease in nitrogen levels for two seasons,with a 29.26% increase in aggregate content above 0.5 mm and a 14.26% increase in aggregate content below 0.25 mm;There are significant differences in the effects of high and low nitrogen levels on aggregates in the two seasons of the experiment.The previous season promoted the formation of small aggregates,while the latter season was conducive to the formation of large aggregates.Micro plastics have no significant impact on soil bulk density,but have a certain impact on soil respiration rate.The decline of micro plastics in high and medium nitrogen levels reduces the soil respiration of two season maize in the big bell mouth stage,and the decline in low nitrogen levels reduces the soil respiration rate of two season maize in the whole growth period.(3)Compared with the absence of microplastics,microplastics increased nitrate nitrogen content by 13.07% and ammonium nitrogen content by 5.3% in the 0-100 cm soil layer during the tasseling stage of two crops of corn at high nitrogen levels;Under the medium nitrogen level,the nitrate nitrogen content and ammonium nitrogen content in the0-100 cm stage of two maize seasons increased by 33.42% and 25.19% respectively,while the nitrate nitrogen content and ammonium nitrogen content in the 0-100 cm stage of two maize seasons increased by 19.24% and 49.88% respectively;Under low nitrogen levels,the ammonium nitrogen content significantly increased by 100.67% from 0 to 100 cm during the flowering period of the following season.Microplastics have no effect on soil organic matter content,but have a significant impact on soil total nitrogen in the following season,significantly reducing total nitrogen content by 30.55% at medium nitrogen levels.(4)Compared with the absence of microplastics,microplastics promoted root growth,increased plant height,stem diameter,and biomass during maize elongation at three nitrogen fertilizer levels,but had no significant effect on the later growth of maize.The effect of microplastics on the total nitrogen content of various organs in maize showed significant differences in two years of experiments.Under three nitrogen fertilizer levels,it promoted the transport of nitrogen from the previous season’s stem to leaves and grains,and inhibited the transport of nitrogen from the following season’s stem to leaves and grains.(5)Compared with the absence of microplastics,each experimental treatment had a significant impact on the yield and water and fertilizer of the previous season of corn.Under high and low nitrogen levels,microplastics reduced yield by 2.12% and 11.81%,water use efficiency by 3.16% and 15.13%,and nitrogen fertilizer use efficiency by14.31% and 32.59%,respectively;It is worth noting that microplastics improved the yield and water and fertilizer utilization efficiency of two crops of corn under medium nitrogen levels,especially significantly increasing the yield of the following season by 3.07%.In summary,this study indicates that microplastic residues can promote the growth of dryland maize by improving soil moisture retention,especially at medium nitrogen levels,with a strong yield increase effect.The influence of micro plastic residue on the composition and structure of soil aggregates and the dynamics of available nutrients varied greatly,and did not show a consistent rule during the test period,but could significantly reduce soil respiration.Overall,in the short term,the impact of microplastic residues on soil physicochemical properties is not as significant as the impact of nitrogen application differences,but its long-term effects still require continuous observation and verification. |
