Accumulation And Translocation Of Potassium In Flue-cured Tobacco

Potassium is the "quality element"in flue-cured tobacco. A high level of K is known to promote the flavor and combustibility of cigarette leaf and reduce the tar content of cigarette smoke as well as favorably influence the physical properties of cured leaf; such as color, body, texture and elasticity. In addition, cured leaf with high concentration of K has a good taste. In those countries producing high quality flue- cured tobacco such as USA and Zimbabwe, potassium content in cured leaf often ranges from 4% to 6% which is nearly 2-3 times as high as that in China. Low leaf K content has been one of the main obstacles to producing high quality flue-cured tobacco. The primary thrust of this thesis is to study some aspects affecting potassium accumulation and translocation in flue-cured tobacco. In view of problems of low K use efficiency and low leaf K content, solution culture experiments, soil culture experiments and field experiments had been conducted during 1999-2000. Cv. K326 was used to study the effects of dose and timing of potassium application, ratio of N/K in tobacco fertilizer, water stress, foliar leaching, relationship between sink and source on potassium accumulation and translocation in flue-cured tobacco. The results are as follows: I. Application of potash in split doses to the soil increases leaf K content. Potassium application in later stage of growth is very important to elevate leaf K content. Under adequate potassium and optimum water conditions, almost 50 percent of total K accumulation would be absorbed after alabastrum appearing. Top dressing in later stage is very useful to enhance the K content of middle leaf and upper leaf In China, K fertilizer has been almost all basal, only a small portion of the total fertilizer is top dressing in early stage. In the south, the rainfall during the entire cropping period is high, which often brings about powerful eluviation of K so that K in soil couldn't meet the later growth needs. Therefore, split application of K fertilizer should be a good proposition for raising the soil K level and leaf K content. 2. In grand growth period, low external osmotic potential caused by PEG-6000 solution has stimulated K accumulation in leaves, stem and roots. High osmotic stress results in an increased membrane permeability to K and rapid efflux of K from the roots. Loss of K increased as a function of time. Tobacco plant is very susceptible to drougt stress in grand growth stage. Keeping a optimum soil moisture is prerequisite to not only raising K uptake, but also reducing K efflux from roots. 3. Tobacco growth is rapidly impaired by oxygen deficiency. During anoxia, dry weight of different organs of flue-cured tobacco is reduced, so does K accumulation. Grave anoxia causes rapid efflux of K from hypoxic roots. In grand growth period (about 25 days after transplanting), when the nutrient solution is made anaerobic by flushing with N2 gas at the rate of 0.5 L/mm, leaves, stem and roots dry weight decreased by 31.06%, 48.16% and 36.9 1%, respectively, compared with control. The rate of K efflux from hypoxic roots is 2.61 times as high as that from normal plant roots. The increased K efflux results in net I