Tobacco (Nicotiana tabacum) is believed to have originated from South America. Present world production is about 6.3 million tons of leaves from 4.2 million ha. (FAOSTAT, 2001).
The crop can be broadly divided according to the method of curing the leaves flue, fire, air or sun-cured. In general, the dark-coloured air and fire-cured tobacco is used for pipe and cigar tobacco, whereas the light-coloured flue and sun-cured is used for cigarette tobacco.
Tobacco is grown under a wide range of climates but requires a frost-free period of 90 to 120 days from transplanting to last harvest of leaves. Optimum mean daily temperature for growth is between 20 and 30°C. A dry period is required for ripening and harvest of the leaves. Excess rainfall results in thin, lightweight leaves. Sun-cured or oriental tobacco requires a relatively dry climate to develop its full aroma. Except for some short-day varieties, cultivated tobacco is day-neutral in its response to flowering.
A light, sandy soil is required for flue-cured, light tobacco. Air-cured, dark tobacco is grown on silty loam to clay loam soils, while fire-cured and air-cured, light tobacco is mostly grown on medium textured soils. The crop is sensitive to waterlogging and demands well-aerated and drained soils. The optimum pH ranges from 5 to 6.5. Quality of the leaves is affected by soil salinity. Depending on the type of tobacco, fertilizer requirements vary and in general are 40 to 80 kg/ha N, 30 to 90 kg/ha P and 50 to 110 kg/ha K.
Tobacco is sown on seed beds and is transplanted 40 to 60 days after sowing when the plants are about 15cm tall. During the first weeks the seedbeds are often covered to protect the young seedlings against unfavourable weather. Spacing after transplantation caries with variety and is generally between 1.2 to 0.9 x 0.9 to 0.6 m. Crop rotation after one or two seasons is recommended with crops such as grass, sorghum, millet and maize that are not susceptible to root eelworm.
To produce high value leaves, topping (removal of flower buds) and desuckering (removal of side shoots) is often practised. Time and height of topping depends on the type of tobacco but is usúal1y done when 10 percent of the plants have their buds in flower.