Characteristics Of Soil Nitrogen Supply And Its Effect On The Nitrogen Nutrition Of Flue-cured Tobacco

Laws of absorption, accumulation and distribution of nitrogen in flue-cured tobacco under different cropping patterns were studied by 15N tracing technique in Jinsha County, Guizhou Province which is main tobacco-producing areas of China. Combined with in situ incubation field experiments, the relationship between soil nitrogen mineralization and tobacco nitrogen nutrition and tobacoo-soil system nitrogen balance were researched. The soil nitrogen mineralization and its simulation were studied by indoor cultivation methods with a combination of in situ incubation experiments during growing stage of flue-cured tobacco. The main findings are as follows:1 The accumulation dynamics of dry matter and nitrogen in flue-cured tobacco were slow- fast– stable type on dryland soil with maize-tobacco rotation and slow - slowly continued increase type on paddy soil with rice-tobacco rotation. It is conducive to uptake soil nitrogen for flue-tobacco on dryland soil with maize-tobacco rotation before topping (60 days after transplanting) and uptake soil nitrogen for flue-tobacco on paddy soil with rice-tobacco rotation after topping.2 The nitrogen utilization efficiency of rapeseed cake, rice straw and rape straw were 19.5%, 15.5%, 8.1% respectively, and the inorganic fertilizer nitrogen utilization efficiency were 41.1%, 42.7% and 35.7% under the combined application of organic additives and inorganic nitrogen fertilizer. The contribution rate of rapeseed cake, rice straw, rape straw to accumulated nitrogen of flue-cured tobacco were 1.0%, 2.4%, 2.7% respectively by the combined application of organic additives and nitrogen fertilizer. Flue-cured tobacco for organic nitrogen absorption meet with the nitrogen needs laws of high-quality tobacco, indicating that the combined application organic additives and inorganic nitrogen fertilizer reduces the nicotine content of tobacco, an increase of sugar/nicotine ratio and improved the quality of tobacco. In which the role of rice and rape straw is greater than the rapeseed cake can be used as measures to lower nicotine.3 Nitrogen accumulation in flue-cured tobacco with the total nitrogen input was a significant positive correlation during the growth stage of flue-cured tobacco. The total nitrogen input for the 156.3-405.5kg.hm-2, in which the soil nitrogen mineralization capacity account for 22.6% -54.3%, with an average of 34.5%, that is, soil nitrogen mineralization accounted for 1/3 of the total nitrogen input. Utilization efficiency of nitrogen fertilizer for the 31.4% -42.7%, tobacco nitrogen use efficiency in paddy soil above that of in dry land crop rotation soil. The apparent loss of nitrogen with total nitrogen input was also significantly positive correlation, tobacco apparent loss rate of nitrogen was for 37.5% -57.2%, with an average of 46.9 percent, about half of total nitrogen input.4 In flue-cured tobacco growth period, the supply of soil nitrogen mineralization in two peaks, one at the flue-cured tobacco rapid growing stage (49 days after transplanting), the second is after topping stage (77 days after transplanting). During growth of the flue-cured tobacco, with the advance of time the cumulative increase in nitrogen mineralization, to flue-cured tobacco for about 91 days after transplanting, the cumulative amount of nitrogen mineralization tends to slow. Soil organic matter content on soil nitrogen mineralization rate dynamics was not significant, the use of nitrogen fertilizers leads to soil nitrogen mineralization dynamics large fluctuations. The soil mineral nitrogen was net fixed in early growth stage of flue-cured tobacco and net mineralization were excited to have a significant effect in the late growth stage. Rapeseed Cake applied 21 days after the soil has begun to generate a net mineralization, rice straw and rapeseed straw in the soil applied 49 days to start the release of inorganic nitrogen, to increase the soil nitrogen mineralization rate in the late growth satge, forming a mineralization rate dynamic which lower in early growth stage and higher in late growth stage.5 Soil nitrogen mineralization dynamics under fluctuated temperature markedly differ from soil nitrogen mineralization under constant temperature incubation. The accumulated temperature model could fit the best of the dynamic accumulation of mineralized nitrogen under fluctuated culture temperature. Index model can better describe the response of soil organic nitrogen mineralization to soil moisture content. A soil nitrogen mineralization model was created based on temperature and soil moisture, could to predict soil nitrogen mineralization in field by using the effective temperature and soil moisture content data.6 Mineralization potential of planting tobacco soil was for about 130.6mg.kg-1 in china, with higher N-supplying. Soil N-supplying potentials were significant differences among in different regions and different soil types, in which mineralization potential of soil on average 170.2mg.kg-1 in Guizhou Province. National Tobacco soil sample analysis results showed that there were significant relationship between soil nitrogen mineralization potential and soil organic matter content, so a model was established on soil organic matter content to predict the soil nitrogen mineralization potential.