Nitrogen Transformation Characteristics Of Reclaimed Soil Under Coal Mining Subsidence Area With Different Fertilizer Application

Soil organic nitrogen pool capacity is an important index to evaluate the effect of soil reclamation and fertilization.The experiment was conducted on the long-term experimental base of reclaimed soil to study differences in nitrogen morphological features and characteristics of nitrogen mineralization,nitrif ication and denitrif ication in soil under five fertilization treatments.The fertilization treatments including no-fertilizer control(CK),single fertilizer(CF),single organic manure(M),fertilizer combined organic manure(MCF)and fertilizer combined with organic manure and phosphobacterin(MCFB).In addition,the dynamic transformation of different forms of exogenous nitrogen after application to the soil were explored through the 15 N tracer technology.This paper reveals the response mechanism of nitrogen accumulation and transformation in reclaimed soil to different fertilization treatments in order to provide a theoretical basis for the reconstruction of the soil nitrogen pool and rational fertilization in the mining area.The main conclusions are as follows:(1)With the increase of reclamation years,the total organic nitrogen content(TON)and the different morphological organic nitrogen content in the mining area increased,but they were still s ignif icantly lower than the surrounding farmland.The TON content was the highest in M treatment in reclaimed soil for 8 years under different fertilization treatments,but there was no significant difference with MCF and MCFB treatment.Compared CK treatment,M treatment signif icantly increased the contents of LFON,HFON and nitrogen management index(NMI)after 8 years of reclamation.The contents of LFON,HFON and NMI in the M treatments were 45.19%,34.49% and 49.77% higher than that of CK,respectively.MCF B treatment signif icantly increased the acid hydrolyzed labile fractions and labile index,and reduced the recalcitrance index than CF treatments.In the density fractionation and acid hydrolysis fractionation,soil HFON and recalcitrant fraction organic nitrogen accounted for 54.97%~77.16% and 55.68%~82.97% of soil organic nitrogen,respectively,which were the main components of soil organic nitrogen.Correlation analys is showed that there was a signif icant positive correlation between soil organic nitrogen in different fractions.The correlation coefficients of LFON and total labile fraction organic nitrogen,HFON and recalcitrant fraction organic nitrogen were 0.9023** and 0.9469**,respectively.(2)These results showed through indoor incubation experiments: As the years of reclamation increased,both cumulative mineralized nitrogen(Nt)and potentially mineralizable nitrogen(N0)had increased,while mineralization rate(Nt/N)and the proportions of N0 to total N(N0/N)did not significant change.Compared with CF treatment,the values of Nt,N0,Nt/N and N0/N increased 65.22%,65.21%,60.42% and 60.76% in 8 years of reclaimed soil with MCFB treatment,respectively.Nitrification rate and the time the maximum nitrif ication rate(Tmax)did not have signif icant difference with the change of the years of reclamation,and nitrif ication rate of different fertilization treatments was higher than CK treatment,but there was no signif icant difference between treatments.The maximum rate of nitrification(Vma x)increased with the increase of reclamation years.MCFB treatment could improve Vma x and Tma x more effectively than other treatments.Nitrate loss and nitrate disappearance rate increased with the increase of reclamation age.After 7 days of cultivation,the nitrate loss was the highest in M treatment,reaching 78.72%,and the nitrate disappearance rate was the lowest in MCF B treatment in reclaimed soil for 4years under different fertilization treatments.There was no signif icant difference in soil nitrogen denitrif ication in different treatments after 8 years of reclaiming soil.The sequence of short-term nitrogen transformation intensity was nitrification >denitrification> mineralization.(3)These results showed that nitrogen in reclaimed soil presented Ammonia N(AN)> Amino acid N(AAN)> Non-hydrolysable N(NHN)> Amino sugar N(ASN),hydrolysable unknown N(HUN)> NO3--N> NH4+-N through the 15 N tracer technology.With increasing reclamation age,acid hydrolyzed organic nitrogen(HN),AAN,HUN and NHN increased by 4.75%~9.18%,11.78%~29.25%,6.03%~29.79% and 9.49%~144.10%,respectively.ASN of reclaimed soil for 8 years decreased by 12.21%~36.52% compared with its of reclaimed soil for 4years.AN and inorganic nitrogen were not signif icantly changed with the increase of reclamation years.HN is the main body of organic nitrogen in reclaimed soil.Compared with other treatments,M treatment was highest on soil organic nitrogen content.When external nitrogen was applied to reclaimed soil,5.92%~16.40% was absorbed by plants,29.92%~67.65% was left in the soil and 21.55%~61.51% was lost.The order of the proportion of exogenous nitrogen in the different morphological organic nitrogen in reclaimed soil: HUN,NHN(1.91%~16.32%)>NO3--N,AN(0.79% ~10.25%)>ASN,AAN,NH4+-N(0.10%~6.92%).In the process of soil transformation,the external fertilizer nitrogen was mainly converted into AN and NHN,while the external organic fertilizer nitrogen was mainly converted into HUN and NHN.In addition,according to the path analysis,the residual nitrogen in the soil was directly affected by ASN,AN,HUN and NHN,and the path coefficients are 0.17,0.24,0.32 and 0.64,respectively.Other nitrogen components had no significant effect on residual external nitrogen.On the whole,long-term fertilization had a significant effect on rebuilding the soil nitrogen pool in the reclaimed area,and it promoted nitrogen transformation while increasing soil nitrogen accumulation.Compared with other fertilization measures,the addition of organic fertilizer was more conducive to the maintenance and improvement of soil available nitrogen.