| Cigar tobacco is a kind of cash crop with high nitrogen demand,which needs to be satisfied by the application of nitrogen fertilizer.However,local tobacco farmers often put in a large amount of nitrogen fertilizer,although the yield of cigar tobacco is increased,but a large amount of unabsorbed nitrogen remains in the soil,which is easy to be dissolved or volatilized,causing environmental problems such as air and groundwater pollution,which is not conducive to the sustainable and healthy development of cigar tobacco.Therefore,in this paper,six different pure nitrogen levels（0,60,120,150,180 and 240 kg/hm2,denoting as N0,N60,N120,N150,N180 and N240）were set through field test with Decue No.3（Cigar Wrapper）and Decue No.1（Cigar filler）cigars as test materials.To analyze the nitrogen absorption,utilization and distribution rules of different genotypes of cigar tobacco,to explore the nitrification and denitrification cycle process of tobacco soil nitrogen and nitrogen metabolism process of tobacco leaf,to study the effect of optimal nitrogen application on nitrogen utilization and soil-cigar nitrogen balance,and to further analyze the whereabouts of fertilizer nitrogen under optimal nitrogen application conditions combined with 15N isotopes.To provide a theoretical basis for rational nitrogen application in cigar planting in Shifang city,Sichuan Province.The results are as follows:（1）In nitrification of tobacco planting soil,ammonia-oxidation process is mainly dominated by ammonia-oxidizing archaea,and nitrite reduction process is mainly dominated by nitrite reductase nir S gene.In addition,nitrification is stronger than denitrification.With the increase of cigar tobacco ripening time,the GS enzyme activity of Dexue No.3 and Dexue No.1tobacco leaves basically did not change much,and the amino acid content showed a decreasing trend.The NR enzyme activity of Dexue No.3 reached the maximum value on 75 days after transplanting,and the protein content of Dexue No.3 and Dexue No.1 tobacco leaves reached the maximum value on 59 and 75 days after transplanting,respectively.Only De Xue No.1cigar tobacco NR enzyme activity regularity is not strong.Nitrogen application had little effect on nitrogen fixation.The gene abundance and nitrogen metabolism of nitrogen cycling microorganisms in tobacco planting soil with different genotypes were different with increased nitrogen application.（2）With the advance of cigar transplanting time,the period of rapid accumulation of dry matter and nitrogen was from 28 days to 59 days after transplanting,and the nitrogen content basically showed a trend of decline.The proportion of dry matter and nitrogen accumulation and distribution in tobacco leaves decreased continuously,while the proportion of dry matter and nitrogen accumulation and distribution in roots increased continuously.In addition,the proportion of nitrogen content and nitrogen accumulation and distribution was in the order of leaf>stem>root.However,the proportion of dry matter accumulation was leaf>stem>root from day 1 to day 59 after transplantation,and stem>leaf>root from day 75 to day 91 after transplantation.With the increase of nitrogen fertilizer,dry matter and nitrogen accumulation basically increased first and then decreased,and N150 treatment had a better performance during the whole growth period.（3）With the increase of nitrogen application rate,the nitrogen apparent use efficiency of Dexue No.3 and Dexue No.1 cigar increased first and then decreased,while the nitrogen partial productivity decreased.Only the seasonal recovery use efficiency,fertilizer economic use efficiency and nitrogen agronomic efficiency were different.The application of nitrogen promoted the increase of the output value of cigar tobacco,and the proportion of grade 1 and grade 2 tobacco leaves.Once the application of nitrogen was excessive,the increase effect gradually slowed down,and the proportion of high-quality grade 1 and grade 2 tobacco leaves decreased.Compared with other nitrogen application treatments,the output value of N150treatment was slightly lower than that of N180 and N240 treatments,and the total proportion of grade 1 and grade 2 tobacco leaves with the highest nitrogen use efficiency and high quality was more than 80%.（4）With the increase of soil depth,the contents and reserves of soil total nitrogen and mineral nitrogen basically decreased.In some treatments,the contents and reserves of total nitrogen and mineral nitrogen in soil depth increased,but the increment was small.Nitrogen application can increase the content and reserves of total nitrogen and mineral nitrogen in 1 m soil layer,among which the content and reserves of ammonium nitrogen in N120 treatment are the lowest,but the content and reserves of nitrate nitrogen are higher.Therefore,the content and reserves of total nitrogen and mineral nitrogen in N150 treatment are relatively small,which can effectively reduce nitrogen loss.（5）With the increase of nitrogen application rate,nitrogen loss,nitrogen balance coefficient and nitrogen balance rate also increased,and soil nitrogen surplus changed from deficit to surplus.The nitrogen surplus of soil nitrogen application rate of 0～60 kg/hm2 was in deficit state,and the nitrogen surplus of soil nitrogen application rate of 120～240 kg/hm2 was in surplus state.The N balance rate of N180 and N240 treatments were 44.54%and 98.38%,and the N surplus was more than 20%,while the N balance rate of N120 and N150 treatments were11.98%and 9.00%,and the N surplus was less than 20%,which was conducive to the soil N balance.（6）The 15N isotope test showed that the nitrogen absorbed by cigar smoke mainly came from fertilizer nitrogen;The proportion of nitrogen accumulation and distribution in all organs in Dexue No.1 cigar was stem>middle>upper leaf>lower leaf>root>flower.With the increase of nitrogen application rate,the proportion of fertilizer nitrogen absorption will increase,and the proportion of soil nitrogen will decrease.The dry matter and nitrogen uptake,fertilizer nitrogen uptake,soil nitrogen uptake and fertilizer nitrogen utilization rate of optimal N application（N150）were higher than those of conventional N application（N180）,and the loss and loss rate of fertilizer nitrogen were lower than those of conventional N application.Therefore,when the nitrogen application rate is 150 kg/hm2,it is beneficial for cigar tobacco to absorb and utilize fertilizer nitrogen efficiently. |
