Effects Of Nitrification Inhibitors On Purple Soil Nitrogen Transformation Processes And N₂O Emissions

Purple soil is a kind of non-zonal soils in subtropical area,it is also one of the important dry-farming soils in south China.Purple soils in the Sichuan Province are characterized by weak nitrogen retention,because of their strong nitrification.Nitrate leaching and runoff are important pathways of nitrogen loss and key nitrogen pollution source.It is urgent to solve the problems of high nitrogen fertilizer application but low nitrogen efficiency,and pollution caused by nitrogen fertilizer application.In order to investigate the effects of nitrification inhibitors on purple soil nitrogen transformation processes and N₂O emissions,firstly,we explored the variability of soil inorganic nitrogen content,nitrification rate,and N₂O production rate.This was done after the addition of nitrification inhibitors?DCD,DMPP,Nitrapyrin,MHPP?and nitrogen fertilizers to the calcareous and acid purple soils.The calcareous purple soil was compared with an acid purple soil obtained after incubation experiments.Secondly,soil gross nitrification and mineralization rates,production paths of N₂O and fraction of nitrified-N emitted as N₂O of calcareous purple soils were analyzed after the above four nitrification inhibitors addition by a ¹⁵N dilution incubation experiments.Finally,an anaerobic¹⁵N-tracing experiment was conducted to measure the denitrification potential and associated gas production in calcareous purple soils after the addition of nitrification inhibitors?DMPP,Nitrapyrin,MHPP?and Glucose with nitrogen fertilizers.We get the following conclusions:?1?Our results showed that four nitrification inhibitors successfully impeded the conversion of NH₄⁺to NO₃^-and reduced the emissions of N₂O for both soils;The inhibitory efficiencies of nitrification inhibitors on the calcareous purple soil nitrification rates were:MHPP?93%¹93%?>Nitrapyrin?91%¹91%?>DMPP?9%⁵8%?>DCD?6%¹4%?,while the efficiencies on the acidic purple soil nitrification rates were:MHPP?76%¹16%?>Nitrapyrin?62%¹09%?>DCD?59%⁷5%?>DMPP?26%⁴3%?.The inhibitory effects of nitrification inhibitors on the total N₂O production in the calcareous and acidic purple soils were 46%⁷6%and 32%⁵4%,respectively.?2?The addition of four nitrification inhibitors can reduce the gross nitrification rate of calcareous purple soils significantly,but influence on the gross mineralization rate not significant.During the whole culture period,the inhibitory efficiencies of nitrification inhibitors on the calcareous purple soil average gross nitrification rates were:Nitrapyrin?97%?>MHPP?85%?>DCD?35%?>DMPP?32%?.DCD,DMPP and Nitrapyrin could inhibit soil N₂O total production by 73%,77%and 65%,respectively,while the N₂O total production of MHPP treated soil was 3.5 times that in CK treated soil.The contribution of nitrification process to N₂O production was 71%⁸9%in all treatments,and MHPP could reduce this contribution proportion significantly.The addition of these nitrification inhibitors all reduced the fraction of N₂O in nitrification products significantly.?3?The addition of nitrification inhibitors and Glucose had no significant effect on the denitrification potential of calcareous purple soils,which was at the following levels of CK:0.44 mg N kg^-1·h^-1,DMPP:0.44 mg N kg^-1·h^-1,Nitrapyrin:0.44 mg N kg^-1·h^-1,MHPP:0.46 mg N kg^-1·h^-1,Glucose:0.42 mg N kg^-1·h^-1.The fraction of N₂O production in N₂ and N₂O total production accounted for0.50%⁰.55%in each treatment,and N₂ was the main production of denitrification.Glucose and DMPP inhibited the total production of N₂ and N₂O in the calcareous purple soils by 3.37%and 0.24%,respectively,and Nitrapyrin and MHPP increased the total production respectively by 0.52%and 5.92%.In summary,the above nitrification inhibitors can inhibit the nitrification effectively,and have no significant direct influence on the denitrification.DCD,DMPP and Nitrapyrin showed high inhibitory effects on N₂O production rate of the tested soils,and the effect of MHPP on N₂O emission was different due to nitrogen fertilizer types and doses.Our results provide a theoretical basis for the field application of nitrification inhibitors to purple soils,encouraging the use of moderate amounts of nitrogen fertilizers,and reducing the environmental risk linked to the use of nitrogen fertilizers.