Effects Of Enhanced Efficiency Nitrogen Fertilizers Under Black Plastic Mulch On Soil Fertility And Ecosystem Multifunctionality Of Spring Maize In Semi-arid Region Of Northwest

Healthy soil is essential for crop productivity,environmental quality and human health.For a long time,excessive nitrogen fertilizer application has existed in the semi-arid region of Northwest China,resulting in low nitrogen use efficiency and crop yield and threatening soil health.The enhanced efficiency nitrogen fertilizers（urease inhibitors（NBPT）,nitrification inhibitors（DCD）,polyolefin coated controlled-release urea（RCN）;EENFs）have been proved to be an effective way to reduce soil nitrogen（N）loss and improve crop N use efficiency.However,the effects of EENFs on soil quality（SQI）and soil ecosystem multifunctionality（EMF）and their internal relations are still unclear.Meanwhile,the positive effects of EENFs on crop yield are easily affected by environmental factors and agricultural management measures（i.e.film mulching）.Therefore,based on a field experiment starting in 2019,this study investigated the effects of different fertilization strategies（no nitrogen fertilizer（N0）,mineral nitrogen fertilizer（N200）,DCD,NBPT and RCN）under black plastic film on maize aboveground biomass,maize yield and crop N use efficiency in the semi-arid region of northwest China（Dingxi City,Gansu Province;Guyuan City,Ningxia Province,Xianyang City,Shaanxi Province;Shuozhou city,Shanxi Province）.In addition,in order to comprehensively evaluate the effects of EENFs on soil quality,microbial metabolism characteristics,and soil EMF by measuring soil physical and chemical properties,microbial biomass carbon（MBC）and microbial biomass nitrogen（MBN）contents,and soil enzymes activities,which provide a theoretical basis for applying EENFs to improve spring maize yield and maintain cropland soil ecological health.The results are as follows:（1）At four study sites,nitrogen inhibitors（NIs）and RCN were beneficial to increase the mineral nitrogen content in the surface soil at different maize growth periods.At the maize silking period（R1）,compared to mineral nitrogen fertilizer（N200）,DCD increased the mineral nitrogen content by 6.78%-22.37%,NBPT by5.14%-16.86%,and RCN by 5.42%-21.51%,respectively.Meanwhile,the NIs had lower apparent N mineralization rate at R1 period,and the main mineral nitrogen form was NH₄⁺-N,which indicated that NIs had strong nitrification inhibition effects.At the maize maturity period（R6）,DCD increased mineral N content by8.63%-57.55%,and NBPT increased by 8.11%-73.59%,while RCN only increased mineral N content at Gansu and Shanxi study sites.In addition,NIs improved SQI mainly by increasing available nitrogen（AN）,MBC and MBN contents.Compared with mineral nitrogen fertilizer（N200）,DCD and NBPT increased SQI by7.61%-16.80%and 2.61%-23.20%,respectively,at four study sites.（2）The EENFs（especially NIs）could change the soil carbon,nitrogen and phosphorus cycling enzyme activities in different periods.The results of enzyme stoichiometry showed that microorganisms were mainly limited by nitrogen at R1 and R6 periods.EENFs fertilizer（especially NIs）application could alleviate microbial N limitation,and ultimately alleviate microbial C limitation（especially at R6 period）.The Mantel-test results showed that microbial C limitation and N limitations were mainly affected by SQI,soil temperature（ST）and soil water content（SWC）.（3）Nitrogen fertilizer application was beneficial to improve soil EMF in different periods.At the R1 period,NIs improved the soil EMF to a greater extent than N200 and RCN,DCD increased by 205.82%-340.00%and 145.00%-215.47%in Gansu and Shanxi,respectively;NBPT increased by 332.75%-778.59%and364.44%-929.62%in Ningxia and Shanxi,respectively.At the R6 period,the soil EMF of EENFs was higher than that of mineral fertilizer,DCD increased by129.10%-388.68%,NBPT increased by 184.85%-327.35%,RCN increased by97.42%-299.15%,respectively.A random forest model showed that the MBC,MBN and SWC of the SQI factors were the main driving forces of soil EMF.In addition,the higher SQI could promote the improvement of soil EMF.It is worth noting that soil EMF was mainly affected by microbial N limitation rather than C limitation.（4）EENFs were more conducive to improving the miaze dry matter accumulation and yield（grain yield,grain number and 1000-grain weight）than mineral nitrogen fertilizer,and has higher crop N use efficiency（N fertilizer agronomic use efficiency and N fertilizer partial productivity）.Compared with N200,NBPT increased grain yield,grain number and 1000-grain weight by 9.86%-63.62%,4.47%-26.14%and 5.13%-29.61%,repectively,at Gansu,Shaanxi and Shanxi study sites;DCD increased by 17.23%-55.91%,5%-22.27%and 11.70%-27.41%,repectively,at Ningxia and Shanxi sites;RCN increased by 17.02%,7.35%and 6.35%,respectively,in Gansu site.In conclusion,the NIs application under black plastic film in the semi-arid region of Northwest China is an effective way to improve soil quality and ecosystem multifunctionality,alleviate microbial C and N limitation,and ultimately increase crop yield.