Study On The Effects And Mechanism Of Nitrogen Control Measures On The Key Nitrogen Transformation Process Of Calcareous Purple Soil

Purple soil is an important cultivated soil in the hilly area of Sichuan Basin.The p H of most purple soils is alkaline,and soil nitrogen nitrification and denitrification are strong.Due to the non-coupling of nitrogen conversion characteristics of purple soil and its environment,the loss of NO₃ leaching and NH₃ volatilization in purple soil farmland in hilly area of Sichuan Province are large,but the utilization rate of nitrogen fertilizer is very low,which is an important reason for the deterioration of regional water,soil and gas quality.The traditional nitrogen fertilizer management measures for purple soil may be blind,because they are not regulated according to the characteristics of nitrogen transformation in purple soil.Therefore,it is necessary to formulate the control measures of soil nitrogen transformation processes,according to the characteristics of nitrogen transformation in calcareous purple soil,and reveal its microbial mechanism,so as to provide the basis for scientific implementation of nitrogen management and improvement of nitrogen utilization efficiency in purple soil.In this study,¹⁵N isotope aerobic and anaerobic culture experiments were carried out,and formulated control measures（including adding biological nitrification inhibitors and new chemical nitrification inhibitors,as well as straw and biological Carbon）for the nitrogen transformation process.Also,we combined with quantitative PCR and high-throughput sequencing to study:（1）The effect of chemical nitrification inhibitors（DMPP,NID）and two different concentrations of biological nitrification inhibitors（mhpp,NIM1,NIM5）on the primary transformation rate of calcareous purple soil and its microbial mechanism;（2）Effects of single application and combined application of nitrification inhibitor,straw and biochar on the primary conversion rate of calcareous purple soil and its microbial mechanism;（3）Effects of chemical nitrification inhibitors（DMPP）and two different concentrations of biological nitrification inhibitors（mhpp）on denitrification potential of calcareous purple soil under anaerobic conditions and their microbial mechanisms;（4）Effects of single application and combined application of nitrification inhibitor,straw and biochar on denitrification potential of calcareous purple soil under anaerobic conditions and its microbial mechanism.The main conclusions of the study are as follows:（1）In aerobic culture experiment,the inhibition rate of nitrification inhibitor on the net mineralization rate of calcareous purple soil was 48.73%-68.25%,but it had no significant effect on the primary mineralization rate（P>0.05）.The addition of nitrification inhibitor significantly reduced the net nitrification rate and primary nitrification rate（P<0.05）.The inhibition rate of each treatment on the soil primary nitrification rate was:NId（46%）>NIm1（23%）>NIm5（16%）.MHPP mainly suppresses soil nitrification by inhibiting the abundance of AOA;DMPP can simultaneously suppress the abundance of AOA and AOB and thus inhibit soil nitrification.The addition of nitrification inhibition changed the diversity and species composition of AOA and AOB.（2）In this study,single application or combined application of nitrification inhibitor,straw,and biochar can significantly inhibit the net mineralization rate of calcareous purple soil（P<0.05）,and straw treatment has the highest inhibition rate,between 454.3%and 498.62%.The single application of straw and biochar and their combination with MHPP can promote the primary mineralization rate of calcareous purple soil,of which the single application of straw has the highest promotion rate,reaching 48.06%;the combination of DMPP and straw can inhibit the primary mineralization rate of calcareous purple soil,the inhibition rate is 23.65%.All nitrogen control measures can inhibit the net nitrification rate and primary nitrification rate of calcareous purple soil in different degrees.Among them,the treatment of single straw application has the highest inhibition rate of net nitrification rate of 165.26%;the combined application of straw and DMPP had the highest inhibition efficiency of primary nitrification rate of soil,reaching 89.54%.In the treatment of biochar,the combined treatment of biochar and DMPP has the highest inhibition rate of the soil primary and net nitrification rates,respectively 52.34%and26.88%.Biochar inhibited the primary nitrification rate of soil by inhibiting AOB,and straw effectively reduced the nitrification rate of soil by promoting the assimilation of microorganisms.All the nitrogen control measures changed the microbial diversity and community structure.（3）In this anaerobic culture experiment,1%and 5%mhpp and 1%DMPP had no significant effect on denitrification potential and N₂O and N₂ emission of calcareous purple soil（P>0.05）.The addition of 1%mhpp could significantly increase the abundance of nir S（P<0.05）.The addition of nitrification inhibitors changed the community structure of soil denitrifying bacteria,especially DMPP treatment greatly affected the diversity of denitrifying bacteria and the main species composition at genus level.（4）Straw treatment can significantly promote the emission of N₂ and N₂O and denitrification potential of calcareous purple soil（P<0.05）and its promotion rate for calcareous purple denitrification potential is:NIm＿ST（1648.23%）>（1264.98%）>NId＿ST（1254.93%）.This is similar to the effect of straw treatment on N₂ emission of calcareous purple soil.Compared with the control,the N₂O emission of straw treatment increased by 917.96%-963.52%.The other treatments had no significant effect on the denitrification potential and the production of gaseous products.The addition of straw can significantly increase the abundance of denitrifying bacteria,especially nir S（P<0.05）,and change the diversity and community structure,thus promoting the occurrence of denitrification..The other treatments had no significant effect on the abundance of denitrifying bacteria（P>0.05）.In this study,nitrification inhibitors,straw and biochar can significantly inhibit the primary and net nitrification rate of calcareous purple soil by inhibiting the abundance of AOA or AOB.Among them,straw treatment has the highest inhibition rate,because straw can also promote the assimilation of microorganisms.At the same time,straw treatment can promote the denitrification potential and the emission of N₂and N₂O by promoting the abundance of nir K and nir S and changing their diversity and community structure.