Degraded soil aggregation arising from nitrogen(N)fertilization has been reported in many studies;however,the mechanisms have not yet been clarified.Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production.The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents.A 12-year(2008-2019)N fertilization field experiment on a Vertisol was performed,covering a wide range of N application rates(0,360,450,540,630,and 720 kg ha-1 year-1)and including straw management(straw return and straw removal)in a wheat(Triticum aestivum L.)-maize(Zea mays L.)cropping system.Soil samples of 0-20 cm depth were collected from 12 field treatments with 3 replications in 2019.Soil aggregate stability(mean weight diameter(MWD))and contents of soil organic carbon(SOC),glomalin-related soil protein(GRSP),microbial biomass carbon(MBC),and mineral N(NH4+and NO3)were determined.Long-term N fertilization under straw removal conditions reduced soil MWD by 12％-18％at N rates from 0 to 720 kg ha-1 compared to that under straw return(P＜0.05).Soil MWD was positively associated with pH(P＜0.05)and MBC(P＜0.05),but negatively correlated with NH4+(P＜0.05)and NO3-(P＜0.05).Compared with the straw removal treatment,the straw incorporation treatment significantly improved the contents of aggregating agents(SOC,GRSP,and MBC)(P＜0.001),but did not affect that of the dispersing agent(NH4+)(P＞0.05);consequently,it improved soil aggregation.Overall,our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions(H+and NH4+)and the decrease in MBC during soil acidification,especially when the applied N dose exceeded 360 kg ha-1 year-1.Our finding can minimize the negative structural impacts on Vertisol.

Zichun GUO;Wei LI;Mahbub UL ISLAM;Yuekai WANG;Zhongbin ZHANG;Xinhua PENG

State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences,Nanjing 210008(China);Crop Research Institute,Anhui Academy of Agricultural Sciences,Hefei 230031(China);University of Chinese Academy of Sciences,Beijing 10049(China);Bangladesh Agricultural Research Institute,Gazipur 1701(Bangladesh)

土壤圈（英文版）

[1]Zichun GUO;Wei LI;Mahbub UL ISLAM;Yuekai WANG;Zhongbin ZHANG;Xinhua PENG-.Nitrogen fertilization degrades soil aggregation by increasing ammonium ions and decreasing biological binding agents on a Vertisol after 12 years)[J].土壤圈（英文版）,2022(04):629-636

Vertisol,Degraded,NH4+and

Nitrogen,fertilization,degrades,soil,aggregation,by,increasing,ammonium,decreasing,biological,binding,agents,after,years,arising,from,nitrogen,has,been,reported,many,studies,however,mechanisms,have,not,yet,clarified,Elucidating,would,help,structure,sustain,high,production,objective,this,study,was,long,its,association,dispersing,field,experiment,performed,covering,wide,range,application,rates,including,straw,management,return,removal,wheat,Triticum,aestivum,maize,Zea,mays,cropping,system,Soil,samples,depth,were,collected,treatments,replications,aggregate,stability,mean,weight,diameter,MWD,contents,organic,carbon,SOC,glomalin,protein,GRSP,microbial,biomass,MBC,mineral,NO3,determined,Long,under,conditions,reduced,compared,that,positively,associated,but,negatively,correlated,Compared,incorporation,significantly,improved,aggregating,did,affect,consequently,Overall,our,results,indicate,because,increases,monovalent,H+and,decrease,during,acidification,especially,when,applied,dose,exceeded,Our,finding,minimize,structural,impacts

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