The Effect Of Organic Fertilizers And Nitrification Inhibitor On N Transformation,Functional Gene Abundance And GHGs Emission In Two Types Of Soil

This incubation experiment was designed to determine how organic fertilizers and nitrification inhibitor affect nitrification and denitrification and gene abundance in red and calcareous soils.The pH of the soils used for this study were as follows:red soil（pH 4.23 to 5.51）and calcareous soil（pH 7.20 to 8.66）,respectively.The experiment samples were designed with four different treatments as follows:CK（no fertilizer）,U（only urea）,UM（60%urea plus cattle manure）,UMCP（UM+nitrapyrin）.The findings of the study showed that UMCP treatment had a significant effect on the retention time of ammonia ammonium（NH₄⁺）and reduced the nitrate（NO₃^-）production in both red and calcareous soils（P<0.05）,compared with UM treatment.Considering the NH₄⁺/NO₃^-ratio,nitrapyrin readily inhibited this process in calcareous soil,with an inhibitory efficiency of nearly twice as long as that in red soil（up to 36 days）.Our study also found that the potential nitrification rate（PNR）and microbial biomass were strongly affected by urea or urea plus manure application,however,the incorporation of nitrapyrin led to a notable decreased.The UMCP treatment lowered gas emissions,relative to UM.This can be attributed to the inhibition of ammonia oxidizing bacteria（AOB）growth in calcareous soil,and the inhibition of archaea（AOA）growth in red soil.Linear regression analysis showed that PNR were positively correlated with AOB（P=0.048）and especially with AOA abundance（P=0.0014）in red soil,but only correlated with AOB（P=0.0032）in calcareous soil.For CO₂ emission,the flux recorded in the urea plus manure（UM）treatment was 0.093 mg N kg^-1 d^-1,which was the highest.The least in this soil type was seen in the treatment with nitrapyrin（UMCP）,and the value was 0.056 N kg^-1 d^-1.Similarly,in the acidic red soil,the UM emission flux was highest,followed by urea（U）only treatment,and the UMCP treatment was the least.In addition,UM treatment significantly increased the number of two soil denitrifying function genes（nirK,nirS and nosZ）,while the application of CP significantly decreased the copy number of three genes（P<0.05）.There was a significant correlation between nitrite reductase and nirK in acidic soils（P<0.001）,while there was a significant correlation between nitrite reductase and nirS in alkaline soils（P=0.02428）.Through multiple linear regression and random forest analysis,pH,NH₄⁺are the key factors affecting AOA and AOB,while NO₃^-and organic carbon（SOC）are the key factors affecting the abundance of soil denitrifying genes（nirK,nirS and nosZ）.Structural equation model analysis showed that AOA and nirK were the key microbial factors affecting N₂O emission in acidic soil,and AOB,nirS and nos Z significantly affected N₂O emission in alkaline soil.Correlation analysis showed a significant positive correlation between SOC and CO₂emissions in both acidic and alkaline soils（P<0.05）.Therefore,the combined application of organic and inorganic fertilizers with nitrification inhibitors significantly reduced the emission of N₂O and CO₂ in calcareous and acidic red soils.This study can provide theoretical reference and scientific support for building the reasonable fertilization plan in reducing greenhouse gas emission.