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Commodities > Tobacco Background
Information Tobacco is the common name of the plant Nicotiana tabacum and, to a limited extent, N. rustica and the cured leaf that is used, usually after aging and processing in various ways, for smoking, chewing, snuffing, and extraction of nicotine. This article deals with the farming of tobacco from cultivation to curing and grading. Cultivation Though tobacco is tropical in origin, it is cultivated throughout the world. N. tabacum requires a frost-free period of 100 to 130 days from date of transplanting to maturity in the field. N. rustica, which is grown to some extent in India and certain Transcaucasian countries, matures in advance of N. tabacum. The prime requisite for successful tobacco culture is a supply of well-developed, healthy seedlings that is available at the proper time for transplanting. Orinoco strains of seed are sown to grow leaf for flue curing. The Pryor group are grown to produce the dark air-cured and fire-cured types. Burley and Maryland strains are seeded for the production of light, air-cured tobaccos. Broadleaf and seed-leaf strains, Havana seed, Cuban, and Sumatra varieties are for the production of cigars. The variety grown for production of Perique resembles the Cuban-like variety used in Puerto Rico. Aromatic varieties are grown for production of this type of leaf and in some degree resemble the Cuban varieties. Soil for a plant bed should be fertile and of good tilth and drainage; it must be protected from chilling winds and exposed to the sun. The soil is usually partially sterilized by burning, steaming, or using chemicals such as methyl bromide to control diseases, weeds, insects, and nematodes (a class of parasitic worms). In warm regions of the world the small germinating seedlings are produced outdoors in cold frames covered with thin cotton cloth or a thin mulch, such as chopped grass (used in particular in Zimbabwe), straw, or pine needles. Glass or plastic is used in colder regions, and close attention is given to watering and ventilation. The usual rate of seeding—i.e., about one ounce (28 grams) of cleaned seed of high germination to 200 square yards (167 square metres) of seedbed area—can be expected, under favourable conditions, to produce 15,000 to 25,000 plants for transplanting. High-analysis mixtures of commercial fertilizers are usually applied before seeding at the rate of one-half to two pounds per square yard (0.3 to 1 kilogram per square metre) of seedbed area. The soil must be finely pulverized and level so that the seed can be lightly covered with soil by rolling or trampling. Uniform distribution of seeds is important. After eight to 10 weeks the seedlings are four to seven inches (10 to 18 centimetres) in length and are ready for transplanting in the field. Transplanting machines are used extensively in some areas, but most of the world's tobacco is planted by hand. When the soil is dry, adding water helps a high percentage of transplants to survive. Fumigation of soil prior to transplanting is a common practice in many areas where nematodes are common; the process helps to reduce the damage caused by their parasitic activity. Harvest Tobacco is harvested 70 to 130 days after transplanting by one of two methods: (1) the entire plant is cut and the stalk split or speared and hung on a tobacco stick or lath, or (2) the leaves are removed at intervals as they mature. The leaves of cigar-wrapper and aromatic tobaccos are strung using a needle, and leaves to be fluecured are looped, using a string tied to a lath or stick that is hung in the curing barn. To prevent breakage and bruising during the handling necessary in curing, it is desirable for the leaf to wilt without sunburning. Tobacco may be left in the field from a few hours to two days to wilt. Curing The three common methods of curing are by air, fire, and flue. A fourth method, sun curing, is practiced with aromatic types and to a limited extent with air-cured types. Curing entails four essential steps: wilting, yellowing, colouring, and drying. These involve physical and chemical changes in the leaf and are regulated to develop the desired properties. Air curing is accomplished mainly by mechanical ventilation inside buildings. Coke, charcoal, or liquid petroleum gas may be burned to provide heat when conditions warrant. Air curing, which requires from one to two months' time, is used for many tobaccos, including dark air-cured types, cigar, Maryland, and Burley. The fire-curing process resembles air curing except that open wood fires are kindled on the dirt floor of the curing barn after the tobacco has been hanging for two to six days. The smoke imparts to the tobacco a characteristic aroma of creosote. The firing process may be continuous or intermittent, extending from three weeks to as long as 10 weeks until curing is complete and the leaf has been cured to the desired finish. The barns for flue curing are small and tightly constructed with ventilators and metal pipes, or flues, extending from furnaces around or under the floor of the barn. Fuels used are wood, coal, oil, and liquid petroleum gas. If oil or gas heaters are used, flues are not needed. Heat is applied carefully, and the leaves are observed closely for changes in their chemical and physical composition. Flue curing requires from four to eight days' time and is used for Virginia, or bright, tobacco. In the process called bulk curing, the leaves are loaded evenly in racks arranged in a curing chamber. Grading After curing, the leaf may be piled in bulk to condition for a time before it is prepared for sale. The preparation consists usually of grading the leaf and putting it in a bale or package of convenient size and weight for inspection and removal by the buyer. Except during humid periods, the leaf must be conditioned in moistening cellars or humidified rooms before it can be handled without breakage. Type of leaf and local custom determine the fineness of grading. At its most elaborate, grading may be by position of the leaf on the plant, colour, size, maturity, soundness, and other recognizable qualities; flue-cured tobacco in the United States and Zimbabwe is graded this way, and each grade bulked or baled separately. Much simpler grading is usual in developing countries, where the buyer is as much concerned with the proportions of each grade as with the quality of the entire lot; aromatic tobaccos are an example of this. Most tobaccos entering world trade, except the aromatic, are assembled before sale into bundles, or hands, of 15 to 30 leaves and tied with one leaf wrapped securely around the butts. Most tobaccos, except aromatic and cigar, are regraded if necessary and usually redried after purchase; then the exact amount of moisture needed for aging is added and the tobacco is securely packed in cases or hogsheads. Exported tobacco is shipped in this form. The trend is for the packing factories to stem the leaf—that is, remove most of the stem leaving the lamina—usually by threshing machines but sometimes by hand, before redrying it. The aging process, particularly with cigar tobaccos, is sometimes hastened by forced fermentation procedures. After purchase, aromatic tobaccos are manipulated; that is, they are factory-graded, baled, and subjected to an elaborate, in-the-bale, fermentation process before going to the ultimate manufacturer. Diseases and pests Common diseases and pests are black root rot, fusarium wilt, tobacco mosaic, bacterial leaf spot, downy mildew or blue mold, black shank, broomrape, and witchweed. These may be controlled by sanitation, crop rotation, the use of sprays and fumigants, and breeding of disease-resistant strains. Resistance to bacterial leaf spot, fusarium wilt, mosaic, black shank, and black root rot have been accomplished by breeding. Some resistant varieties of tobacco in general use have been produced by blending desired characteristics from N. longiflora, N. debneyi, N. glutinosa, and others with some strain of N. tabacum. Common insect pests are the green June beetle larvae, cutworms, and flea beetles in the plant bed and hornworms, grasshoppers, flea beetles, cutworms, budworms, and aphids in the field. The cigarette, or tobacco, beetle damages the stored leaf and sometimes the manufactured product. Insect pests are controlled on the growing crop by using sprays and dusts, on the stored product by fumigating and trapping. Biological control often is effective. Fumigation controls nematodes in the field. Related Links Mbendi - African Tobacco |
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