| ?Object?Increasing nitrogen(N)in broad areas of terrestrial ecosystem through nitrogen deposition and fertilizer will significantly increase the reactive nitrogen content and nitrogen gaseous emissions including N2 O and NH3,resulting in N losses and environmental effects.Based on our previous studies,we aimed to 1)assess the effects of exogenous N inputs on N2 O and NH3 fluxes from a saline soil and its main regulating factor 2)evaluate the influences of combined supplementing of NBPT with CP(DIs)on NH3 and N2 O emission and its main regulating factor;3)explore the effects of salt on N transformation and the variation of NH3 and N2 O fluxes and cumulative emission.All of this could provide knowledge theoretically on how to improve N fertilizer utilization efficiency and decrease the greenhouse gases emission as well as spread the application of urease inhibitor and nitrification inhibitor in saline soil.?Method?The laboratory experiment focused on the effect of DIs and salt on soil N transformation and the variation of NH3 and N2 O fluxes in normal and salt treated soil.The experiment included two soil salt levels: 0.60 ds m-1(normal soil),1.40 ds m-1(salt treated soil).There were also three N levers: CK,Urea(U),Urea+0.5 %NBPT +0.25% CP(U+DIs).The field experiment focused on the changes in soil NH3 and N2 O fluxes following nitrogen deposition and countermeasures by DIs application as well as to preliminarily assess the major influence factors of N2 O and NH3 production with or without inhibitors.The experiment used a single-factor completely random design with three levels: CK,N(50 kg N ha-2 yr-1),N+NBPT+ CP(N+ DIs).?Results?1)Compared with CK,exogenous N inputs can obviously increased soil mineral nitrogen content including soil NH4+,NO3-and NO2-.For instance,regardless of soil types,the NO2-and NO3-concentrations were significantly higher in the treatment of urea addition than in the CK treatment over the whole incubation time,in addition,the average content of NO3-and NO2-increased 89.2 and 8.21 g kg-1,respectively,than that in CK.Urea hydrolysis and nitrification was substantially retarded by the combined addition of NBPT and nitrapyrin(urea +DIs),which finally enhanced the ammonium nutrition and reduced nitrate and nitrite nutrition.For example,the average content of NH4+ in urea and stimulated nitrogen deposition addition increased 35-37 % and 21 %,respectively,while the average content of NO3-decreased 38-39 % and 31 %,respectively.In addition,compared with the normal soil,the average NO3-concentration in the salt-treated soil was decreased by 15.9% in the urea alone,suggesting both urea hydrolysis and nitrification were inhibited by salt addition.2)Exogenous N inputs obvious increased the soil MBC,MBN,total nitrogen,urease,ammonia oxidase,nitrate reductase,nitrite reductase and hydroxylammonium reductase activities(p< 0.05),but have faint influence on SOC.Furthermore,soil urease activity was inhibited and ammonia oxidase,hydroxylammoniumn reductase activities was decreased by urea+Nitrapyrin+NBPT treatment,whereas,improved the nitrate reductase activity,nitrite reductase activities and the content of MBC and MBN.In addition,salt can obvious decreased the urease,ammonia oxidase,nitrite reductase,MBC and MBN(p< 0.05),while have little effects on nitrate reductase and hydroxylammonium reductase activities(p> 0.05).3)Exogenous N inputs obvious increased the soil N2 O flux and cumulative losses,while DIs can significantly decreased the N2 O emission.Compared with only N inputs treatment,the soil N2 O flux(or cumulative losses)in DIs addition treatment obviously declined by 78-80 %(or 79-82 %)from urea input test and 36%(or 28%)from stimulated N deposition test.In addition,the average N2 O fluxes and average cumulative losses were 1.21 g kg-1 h-1 and 146.3 g kg-1 in the normal soil,which were 31.4 % and 38.7 % higher than in the salt-treated soil,indicating salt significantly decreased soil N2 O emission.According to the correlation analysis and stepwise linear regression,we found that soil total nitrogen,NO3-,NO2-,soil volumetric water content of 0-20 and 20-40 cm and 0-20 cm soil temperature were the dominant factors in releasing N2 O.However,these predominant factors were obvious changed by DIs addition.4)Exogenous N inputs obvious increased the soil NH3 flux and cumulative losses,while DIs can significantly decreased the NH3 emission.Compared with only N inputs treatment,the soil NH3 flux(or cumulative losses)in DIs addition treatment obviously declined by 42-45%(or 43-46 %)from urea input test and 199 %(or 187 %)from stimulated N deposition test.Furthermore,salt can increased the NH3 emission(p>0.05).According to the correlation analysis and stepwise linear regression,soil NH4+,total nitrogen and 0-20 cm soil temperature was found dominated in driving NH3 emission and these was also disturbed by DIs.?Conclusion?1)Exogenous N inputs added soil can obviously increased soil NH4+,NO3-and NO2-content,further enhanced the emission of N2 O and NH3 emission.However,DIs can retarded urea hydrolysis and nitrification,resulting in enhanced the ammonium nutrition and reduced nitrate and nitrite nutrition,which will finally reducing the emission of N2 O and NH3 emission.2)Soil total nitrogen,NO3-,NO2-,soil volumetric water content of 0-20 and 20-40 cm and 0-20 cm soil temperature were the dominant factors in releasing N2 O,while,soil NH4+,total nitrogen and 0-20 cm soil temperature was found dominated in driving NH3 emission.However,these predominant factors can obvious changed by DIs addition.3)Urea hydrolysis and nitrification were inhibited by salt addition,which further significantly decreased the N2 O emission while have little effect on NH3 emission. |
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