Nitrification Inhibitory Effect Of Nitrapyrin And Its Microbial Mechanism

Nitrification inhibitors(NIs)are chemicals capable of suppressing ammonia oxidation and have been used as tools to regulate nitrogen transformation in soil,so as to reduce nitrogen loss.2-chloro-6-(tricholoromethyl)-pyridine(CP)was one of the most common NIs in agriculture.CP was recently reformulated with new technology by Zhejiang Aofutuo Chemical Co.Ltd..Unlike the previous form of CP,the purity of the new product has the potential to reach 98%.The nitrification inhibitory effect of CP has improved a lot because of the greatly reduced impurities and it has demonstrated to have a better effect in practice.Yellow clay paddy soil is a typical low-yield soil with low nitrogen use efficiency(NUE)in southern China.CP co-applied with nitrogen fertilizer has demonstrated to improve the rice yield and NUE in yellow clay paddy soil.In our work,a high purity nitrification inhibitor CP was taken as the research object,to study the dosage effect and nitrification inhibition effect of two preparation formulations including emulsifiable concentrate(EC)and water emulsions(EW)in sandy and clayey soils and try to find the optimum dosage;Effect of pH and soil moisture content on the nitrification inhibition effect of CP;Accumulation effects of 5 years application of CP on the abundance and community structure of ammonia-oxidizing archaea(AOA)and bacteria(AOB)in yellow clayey paddy soils;Effects of CP on the dynamic changes of soil nutrients and amoA gene abundances of AOA and AOB in different growth periods of double cropping rice trials.The main results were as follows:(1)Both the EC and EW of CP can significantly inhibit the nitrification process in sandy and clayey soils.On the 30th day of cultivation,the nitrification inhibition rate of EC in sandy and clayey soil were 55.6%-91.4%and 18.5%-50.9%,the nitrification inhibition rate of EW in sandy and clayey soil were 40.0%-79.0%and 35.7%-52.5%.Generally,the inhibitory effect of EC and EW showed better in sandy soil than in clayey soil.The dose effects of EC in sandy and clayey soil were very obvious.The higher the dose,the higher the nitrification inhibition rate.The dose effect of EW was obvious in sandy soil,but in clayey soil the nitrification inhibition rate was not significantly improved when the dose increased higher than 0.2%.The optimum dosage of EC and EW in sandy and clayed soil were 0.3%of pure N.In sandy soil,the nitrification inhibition rate of EC at 0.3%was 88.1%,significantly higher than EW(74.9%)while in clayey soil,the nitrification inhibition rate of EW at 0.3%was 53.3%,significantly higher than EC(47.7%).Therefore,the nitrification inhibitory effect in sandy soil was EC>EW while in clayey soil was EW>EC.(2)The apparent nitrification rate increased with pH and presented at different soil moisture levels was 60%WHC>60%WHC>80%WHC,showed that nitrification was more intense in higher pH soil and at 60%WHC.Nitrification inhibition effect was initially higher in high pH soil but then performed better in low pH soil and lasted longer.Nitrification inhibition rate in soils of moisture levels was 40%WHC>60%WHC>80%WHC,showed that the inhibitory effect was better when soil moisture was lower.In conclusion,CP should be more suitable for application in acidic soil and upland soil.(3)In the yellow clayey paddy soil treated with 5 years urea and CP,application of urea improved potential nitrification rate(PNR),and also significantly stimulated AOA and AOB growth and increased the abundance of AOA and AOB amoA genes.The PNR of the soil was significantly correlated with the abundances of both AOA and AOB.CP decreased PNR and significantly reduced the gene abundance of AOA but showed a less inhibitory effects on AOB amoA genes.Phylogenetic analysis showed that the most dominant operational taxonomic units(OTUs)of AOA and AOB were affiliated with the Nitrosotalea cluster and Nitrosospira cluster 12,respectively,accounting more than 90%.It showed a low ammonia-oxidizing microbial diversity and a stable microbial community structure.Therefore,CP and urea have not altered AOA and AOB community structures.(4)Compared with conventional fertilization of urea,CP combined with urea in one-time base application significantly increased the yield and NUE of double cropping rice.During the whole growth period,CP had no significant effect on soil total nitrogen,nitrate nitrogen and available phosphorus content,while significantly increased the available nitrogen and ammonium nitrogen of tillering stage.CP significantly inhibited the amoA gene abundances of AOA and AOB in the tillering and booting stage and had better inhibitory effect on AOA.Pearson correlation analysis indicated that the yield of early rice and late rice both were significantly positively correlated with soil available nitrogen of tillering,booting and grain-filling stage,and also significantly positively correlated with ammonium nitrogen of tillering stage.Therefore,CP inhibited nitrification by inhibited the amoA gene abundances of AOA and AOB,so that a high concentration of NH4+-N in tillering stage was ensured to provide enough nitrogen and promote plant uptake and utilization,and thereby increasing rice yield and NUE.