Effects Of Three Kinds Of Inhibitors On Soil Nitrification In Long-Term Nitrogen-Addition And Non-Nitrogen Soils

Nitrogen(N)is an essential nutrient element in the process of plant growth and metabolism,which plays an important role in the yield and quality of crops.Nitrogen fertilizers are absorbed and utilized by crops,and they are also lost by volatilization,leaching,and denitrification,which results in low nitrogen utilization.Nitrification is an important N metabolism process in terrestrial ecosystem,which could affect crop production and cause many environmental issues.The common inhibitors have the inhibitory effect by inhibiting ammonia-oxidizing bacteria(AOB)activity.In this study,PTIO and NaClO₃ were used as nitrification inhibitors in the soil,which could inhibit the activity of ammonia-oxidizing archaea(AOA)and complete ammonia-oxidizing bacteria(comammox),respectively.The mechanism and efficiency of PTIO and NaClO₃ in soil remain unclear.Based on ¹⁵N isotope tracer technology,DCD with 4%pure nitrogen was used as a control group to study the nitrification inhibition effects of PTIO and NaClO₃ under the same dosage in the undisturbed soil incubation experiments.This research could be used to provide new target for the development of nitrogen fertilizer efficient utilization,and to provide important reference on the niche study of the three major types of soil ammonia oxidizing microorganisms.The main results were as follows:(1)Urea was completely converted into nitrate within 28 days after being applied to the two soils.In long-term nitrogen-addition(N₂P₂K₂)and non-nitrogen(N₀P₂K₂)soils,DCD and NaClO₃ delayed the conversion of NH₄⁺-N to NO₃^--N,the inhibitory effect of DCD was stronger than that of NaClO₃.PTIO inhibited the transform of NH₄⁺-N in the first 7 days in long-term nitrogen-addition soil.(2)In long-term nitrogen-addition soil,the Mineral-¹⁵N Ndff%(percent of nitrogen derived from fertilizer)reached the highest value on the 7th day of incubation,which was90.88%?103.07%,regardless of whether the inhibitor was applied or not.On the 7th day of incubation,DCD inhibited significantly the conversion of urea to nitrate in both soils,and NO₃^--¹⁵N Ndff%was reduced by 11.53 and 47.79 percentage points,respectively.NaClO₃ inhibited significantly the conversion of urea in long-term nitrogen-addition soil.PTIO had no significant effect on the conversion of urea to nitrate in both soils.(3)In both soils,DCD reduced significantly the total N₂O emissions by 78.9%and 95.4%,respectively.NaClO₃ and PTIO had different effects on soil N₂O emissions in the two soils.In long-term non-nitrogen soil,NaClO₃ reduced the total N₂O emissions by 7.7%,PTIO promoted N₂O emissions by 59.5%.In long-term nitrogen-addition soil,PTIO reduced N₂O emissions by3.2%,NaClO₃ promoted N₂O emissions by 46.4%.PTIO,DCD and NaClO₃ inhibited significantly the ¹⁵N₂O Ndff%in the two soils on the 7th day of incubation.(4)In both soils,DCD and NaClO₃ inhibited potential nitrification rate(PNR),but the inhibition times were diffierent.In long-term non-nitrogen soil,DCD inhibited the soil PNR in5?14 days,NaClO₃ inhibited the soil PNR in 7?21 days.In long-term nitrogen-addition soil,DCD inhibited the soil PNR in 3?14 days,NaClO₃ inhibited the soil PNR on 3rd and 7?14 days.(5)DCD and NaClO₃ inhibited soil nitrification in both soils,and the inhibitory effect of DCD was better than that of NaClO₃.In long-term non-nitrogen soil,DCD and NaClO₃inhibited significantly soil nitrification in the previous month of incubation,the inhibition rates of nitrification were 5.18%?34.58%and 9.36%?26.61%,respectively.In long-term nitrogen-addition soil,DCD nitrification inhibition rate was 7.30%?50.23%,NaClO₃ inhibition rate was7.04%?15.64%in the first 21st day of incubation.PTIO inhibited weakly soil nitrification on the 7th and 21st days of incubation,and the inhibition rates were 2.39%and 1.94%,respectively.In summary,the conversion rate of urea was faster relatively in long-term nitrogen-addition soil than that in long-term non-nitrogen soil.The nitrification inhibitor DCD showed significant nitrification inhibition in both soils.NaClO₃ could also inhibit the conversion of NH₄⁺-N to NO₃^--N,but it had little effect on soil N₂O emission.PTIO inhibited nitrification only in first 7th day in long-term nitrogen-addition soil,and had no significant effect on soil N₂O emission.Therefore,the use of PTIO and NaClO₃ as a new type of inhibitor in soil requires further consideration.