Effects Of Plastic Film Mulching And Nitrogen Application On Soil N₂O Emission And Soil Quality Of Summer Maize Field With Straw Incorporation In Guanzhong

Agricultural production in China is facing challenges of ensuring food security and mitigating farmland greenhouse effect.Straw incorporation is widely used in agricultural production because it is beneficial for improving soil hydrothermal environment and soil fertility.However,the stimulation effects of straw incorporation and nitrogen fertilizer utilization pose a serious risk to greenhouse effect.This has attracted researcher's attention,especially during the summer maize growth period,when the higher temperature and rainy climate can cause more soil N₂O emissions.Therefore,this study advocated an optimal straw-based system,i.e.straw incorporation plus half plastic film mulching(SP),to enhance crop yield,maintain soil fertility,and mitigate the straw-induced N₂O emissions in summer maize field.A three-year field experiment from 2018 to 2020 was conducted to investigate the effect of straw incorporation method including no straw input(S0),straw incorporation(SR)and SP,and nitrogen application rate including routine rate(N1)and 70%of routine rate(N0.7)on summer maize yield,soil N₂O emissions,soil organic carbon storage and physical,chemical and biological properties in topsoil.Eventually,the crop yield,soil N₂O emissions and soil organic carbon storage were comprehensively taking into consideration to get the optimum straw incorporation method.Specific research results were as follows:(1)The physical,chemical and biological properties in topsoil(0-20 cm)were improved by SPFirstly,the soil hydrothermal environment in summer maize field was significantly improved by SP(P<0.05).For the average soil temperature during the summer maize whole growth period,compared with SR,SP increased soil temperature at 5 cm depth by1.12?,1.33? and 0.89?,respectively,during 2018 to 2020.Besides,SP increased soil temperature at 10 cm depth by 0.96?,1.29? and 0.55?,respectively,during 2018 to2020.For the average soil water content during the whole growth period,compared with SR,SP significantly increased soil water content in 2019(P<0.05),but there was no significant difference between them in 2018 and 2020.Secondly,the soil labile carbon and nitrogen pools were significantly improved by SP(P<0.05).With the same nitrogen application rate,SP not only reduced the contents of soil nitrate nitrogen,ammonium nitrogen,dissolved organic carbon,dissolved organic nitrogen,microbial biomass carbon and microbial biomass nitrogen,but also reduced the soil microbial quotient compared to SR.However,in most occasions,SP significantly increased soil nitrate nitrogen,ammonium nitrogen,dissolved organic carbon and dissolved organic nitrogen at jointing to flare opening stage,flare opening to flowering stage and flowering to maturity stage(P<0.05).In addition,SP increased the soil microbial biomass carbon and nitrogen content during flowering to maturity stage.With the same straw incorporation method,reducing nitrogen application rate decreased the soil nitrate nitrogen,ammonium nitrogen and soluble organic carbon and nitrogen content.Thirdly,compared with SR,SP significantly reduced the average activities of soil urease,ammonia monooxygenase,nitrate reductase and ?-glucosidase,but significantly increased the average activities of soil nitrous oxide reductase,cellulase and polyphenol oxidase during summer maize growth period(P<0.05).(2)Soil nutrient contents and carbon sequestration potential of topsoil was increased by N1-SPBoth SR and SP significantly increased the contents of total nitrogen,total phosphorus and available phosphorus in topsoil at the mature stage of summer maize(P<0.05).There was no significant difference between SP and SR in soil total nitrogen content.Compared with SR,SP reduced soil total phosphorus content while increased the contents of inorganic nitrogen and available phosphorus in topsoil.For soil organic carbon storage,compared with S0,SR significantly increased organic carbon storage of topsoil by 10%,18% and 5%in 2018,2019 and 2020(P<0.05),respectively.More importantly,N1-SP soil has greater carbon sequestration potential than SR.This was mainly because N1-SP significantly increased soil water content,dissolved organic carbon,dissolved organic nitrogen,microbial biomass nitrogen,and the activities of cellulase and polyphenol oxidase(P<0.05),which promoted the formation and storage of soil organic carbon.(3)Maize yield was enhanced and soil N₂O emissions were mitigated by N0.7-SP,thus improving the soil quality based on soil N₂O emissions per yieldIn terms of summer maize yield,SP had the best performance in enhancing crop yield,and it significantly increased crop yield by 13%,8% and 24% in 2018,2019 and 2020,respectively,compared to S0(P<0.05).This is firstly because SP increased the contents of soil available nutrients,such as soil nitrate nitrogen,ammonium nitrogen,soluble organic nitrogen,total phosphorus and available phosphorus,providing nutrients for the growth and development of summer maize.Secondly,SP improved the water use efficiency of summer maize,and the explanation rate of water use efficiency for summer maize yield was more than 90%.In addition,SP significantly increased the activities of soil cellulase,?-glucosidase and polyphenol oxidase(P<0.05),promoting the rapid decomposition of returned straw,thus providing nutrients for the growth of summer maize.For the same straw incorporation method,the reduction effect of reducing nitrogen application rate on maize yield was only appeared in 2018.However,with the increase of straw incorporation years,reducing nitrogen application rate had no significant effect on yield in 2019 and2020.For soil N₂O emissions,during the summer maize growth period,the higher soil N₂O emission rate was appeared during sowing to seedling and seeding to jointing.From 2018 to 2020,SP significantly reduced soil N₂O cumulative emission by 11%,25% and 22%during the summer maize growth period(P<0.05),respectively,compared to SR.This is mainly because the SP reduced the substrates and energy sources for microbial nitrification and denitrification,like soil nitrate nitrogen,ammonium nitrogen and soluble organic carbon content compared to SR during seeding to jointing.Moreover,SP reduced the nitrification and denitrification related enzyme activity,like ammonia monooxygenase,nitrate reductase,nitrite reductase and nitric oxide reductase activity compared to SR during seeding to jointing.In addition,the increase of N₂O concentration in soil under plastic film promoted soil microorganisms to secrete more N₂O reductase,which is beneficial to promote the further reduction of N₂O to N2.Soil N₂O emissions per yield combines crop yields with soil N₂O emissions.N0.7-SP mitigated the straw and nitrogen-induced N₂O emission.This is because N0.7-SP not only increased the summer maize yield,but also reduced the cumulative N₂O emission compared with N0.7-SR.Based on soil N₂O emissions per yield,the minimum data set was used to calculate the oil quality index.Compared with SR,SP improved the soil quality index,and this improving effect was better under reduced nitrogen application rate.This was mainly because N0.7-SP decreased the activities of soil urease and nitrate reductase and microbial quotient(MBN/TN)in the topsoil layer,thus increasing the scores of soil quality index in these three aspects.In conclusion,the N1-SP was recommended in this study because it can not only mitigate the straw and nitrogen-induced soil N₂O emission,thus slowing down the greenhouse effect,but also enhance crop yield and soil organic carbon storage of topsoil,thus ensuring food security and agricultural sustainable development.