Abstract: The effects of continuous cropping and rotation system on soil nutrient and soil microflora of tobacco field were studied,and the changes of nitrate nitrogen at different growth stages of flue-cured tobacco with different ratios of ni- trate nitrogen and ammonium nitrogen as base-fertilizer were analyzed 1 The result showed that,comparing to rotation pattern, the 3-year and 6-year continuous cropping tobacco led to the decrease of soil organic matter,the increase of soil available nitrogen,phosphorus and potassium,and the rise of pH.Compared to 3-year continuous cropping,the soil of 6-year continu- ous cropping increased more in pH,available phosphorus and potassium,had the similar level of available N,and decreased in organic matter by 4.3 %.The number of bacteria and actinomyces in soil presented a desending trend with the increase of continuous cropping years.The number of fungi was the lowest in 3-year continuous cropping. The number of effective mi- croorganisms such as bacteria and fungi reduced gradually along with the extension of continuous cropping years,while the number of harmful microorganisms such as pythium increased.The content of nitrate nitrogen in tilth layer increased with an increase of proportion of nitrate nitrogen in base fertilizer during early growth stage.The nitrate nitrogen mainly accumulated in 40 - 60 cm depth of soil as the development of tobacco.Based on the changes of nitrate nitrogen in soil during whole stage of growth,the optimum ratio of nitrate nitrogen in base fertilizer was 30 %- 50 %.

Key words: Flue-cured tobacco, Planting system, Fertilization, Soil nutrient, Soil microflora

CLC Number: 

• S572.047