The Characteristic Of Nitrogen Supply Of Red Soil And Its Contribution To Nitrogen Nutrition Of Flue-cured Tobacco

Soil OM was one of major indexs to assess ability of soil N supply. The experiment was carried out to study the effect of soil OM on characteristics of soil N release, DM and N accumulation of fule-cured tobacco and nicotine accumulation of tobacco leaves after topping and the quality of tobacco leaves by using field training in site, N-free zone biomass absorption method and 15N isotope tracer technique in red soils of three different level of OM content. The main results obtained were as following:The content of soil mineral nitrogen increased along with the increasing of OM content in red soil during the growth of flue-cured tobacco. Nitrogen fertilization could raise soil mineral nitrogen content and its effect could last to 11 weeks after transplant in low and middle OM of red soils, and to the end of harvest high OM content. From 30d to the end of harvest, the content of mineral nitrogen of soil profile decreased in low OM of red soil, and that of non-plantfiled treatment was increased, while N-free and fertilizing N treatments were decreased in middle and high OM of red soils. Red soils of low, middle and high OM content could release 61.8kg·hm-2~71.5 kg·hm-2, 65.5kg·hm-2~95.3kg·hm-2 and 68.5 kg·hm-2~ 104.6kg·hm-2 nitrogen respectively during growth stage of flue-cured tobacco.Leaf areas and ratio of root to shoot of tobacco were affected significantly by soil OM content and nitrogen fertilization, while the ratio of fresh weight to dry weight insignificantly. DM of flue-cured tobacco was accumulated mainly within 11 weeks after transplant, Nitrogen fertilization could raise DM accumulation which increased with the increasing of soil OM content. The distribution of DM in tobacco was arranged by the order of leaves>stem>root, and the percentages were between 45.69% and 59.31%, 22.41% and 29.26%, and 18.29% and 25.74% respectively, meanwhile the percentage of DM of tobacco leaves decreased and that of tobacco stem and root increased with the increasing of soil OM. Nitrogen fertilization could reduced percentage of DM of tobacco leaves decreased, while raised the percentage of tobacco stem and root.Along with the increasing of soil OM, the period of accumulation of total nitrogen, soil nitrogen and fertilizer nitrogen accumulated was extended and the amount increased, and nitrogen fertilization also increased the N accumulation. About 29.07%~40.26% of nitrogen absorbed by flue-cured tobacco was from fertilizer and 59.74%~70.93% from soil, and the percentage of soil nitrogen increased and that of fertilizer nitrogen decreased with the increasing of soil OM. The percentages of nitrogen of tobacco leaves and root decreased and that of tobacco stem increased with the increasing of soil OM, and Nitrogen fertilization could reduced percentage of nitrogen of tobacco leaves, and that of tobacco stem and root raised. The percentage of fertilizer nitrogen was arranged by the order of lower leaves>middle leaves>root>stem>upper leaves and soil nitrogen by upper leaves>stem>root>middle leaves>lower leaves in different parts of tobacco plant.Nitrogen fertilization could raise accumulation of nicotine of tobacco leaves that was arranged by the order of upper leaves> middle leaves>bottom leaves in different parts of leaves. Soil OM content and nitrogen fertilization had significantly effect on chemical component of tobacco leaves. while fertilizing nitrogen, the quality of tobacco leaves increased in low OM soil, bottom leaves and middle leaves increased but upper leaves decreased in middle OM soil, and the quality of tobacco leaves decreased in high OM soil while applicaton of nitrogen reached to 90kg·hm-2.Accumulation of nitrogen of flue-cured tobacco with amount of nitrogen supply had significantly positive correlation. Nitrogen fertilization could raised the amount of N apparent losses, that was arranged by the order of low OM>high OM>middle OM. The utilization efficiency of nitrogen fertilizer was between 25.42% and 30.61% in red soil. The amount of nitrogen fertilizer should be raised up in the soil of low OM content, not changed middle OM and cut down high OM content from the foundation of 90kg·hm-2 nitrogen.