Tobacco Farming
Introduction
Tobacco is an important cash crop. The crop is grown for its leaves, which are used as cured products. Leaves of tobacco plant have high levels of the addictive chemical nicotine. Tobacco is one of the non- food crop that contributes substantially to the economy of more than 150 countries around the globe. It is used as chewing, cigarettes, cigars and other purpose. It is a good source for earning foreign currency.
Climatic requirements and soil
Tobacco is a tropical crop. Tobacco seeds requires about 21˚C temperature for germination. Temperature between 27 and 32˚C are desirable for rapid uniform germination. Tobacco plant grows and matures rapidly when average temperatures are about 25˚C. Lower temperature increases the growth period. During cold weather and at low temperatures there is slow growth of the plants and this also affects the quality of the tobacco. Similarly, during very hot weather and high temperatures there is loss of moisture from the tissues of the plant and as a result of it the leaves become thicker and the aroma becomes stronger. Atmospheric humidity also influences the quality of the leaf and also the yield and curing of the leaves. Droughty conditions along with low humidity affect the quality and yield adversely. A crop which has been subject to a moderate drought throughout growing period produces leaves which are thicker, darker in colour, have more gum, does not ferment well and are inferior in taste and aroma.
The water requirements of the tobacco plant are very high. When it is grown as a rainfed crop, it requires at least 50cm of well distributed rainfall throughout the growing season. Rainfall is undesirable at the time of maturing of the crop as gums and resins on the leaf get washed. Tobacco suffers severe injury from strong winds and hail. Quality of tobacco is greatly influenced by the soil conditions. Tobacco is adapted to moderately acidic soils, with a pH ranging from 5.5 to 6.5. Tobacco will not grow well in water logged soils as it is sensitive to water logging condition.
Varieties
- Oxford
- Maryland
- Sona
- Virginia Gold
- Virginia Bright
- Harrison Special
Land preparation
A clean and well pulverized field of good tilth is needed for transplanting tobacco seedlings. The field is ploughed 2 or 3 months before the seedlings are transplanted. As a rule deep plough with mould board plough and three four cross harrowing are practiced. Each harrowing is followed by planking to make the soil pulverized and leveled.
Sowing
Tobacco seeds are very small and are not sown directly in the field, but are sown in nursery. While the main field is being prepared tobacco seedling are raised in specially prepared seed beds. Much of the success in growing a good crop of tobacco depends on the production of healthy and vigorous seedlings. Usually, at least six to eight weeks are required to obtain transplantable seedlings. Transplanting Seedling with good root system and 5-6 leaves are planted. Transplanting is done in the month of March –April. Seedling are transplanted at a distance of R*R: 50-100cm
Transplanting
Seedling with good root system and 5-6 leaves are planted. Transplanting is done in the month of March –April. Seedlings are transplanted at a distance of R*R: 50-100cm and P*P: 10-60cm.
Manures and fertilizers
In tobacco crop it is a well-known fact that economic returns are largely dependent on the right combination of yield and quality rather than on the yield alone. Quality in tobacco, particularly in the smoking types depends on the balance of the nutrients in the leaf. Heavy manuring with nitrogen increases the yield, but has an adverse effect on the quality. With excess of nitrogen supply, the carbohydrate-nitrogen ratio gets reduced. It is observed that in chewing, bidi and hookah tobaccos better quality is generally associated with higher yields that may be obtained with heavy manuring of nitrogen together with other nutrients. Phosphorous requirement of tobacco is comparatively low. Potash is an important element.
In addition to the inorganic fertilizers, application of organic matter in the form of well-rotten farm yard manure or compost is also recommended at the rate of 6-7 tonns/hac for heavy soils and 10-12 tonns/hac for light soils to improve the physical condition of the soil.
Plant management
Plant management of tobacco includes soil loosening, weeding, top dressing, irrigation, topping and desuckering.
Weed control
Intercultural operations should start after 10-15 days of transplanting when the seedlings are well established. Tobacco is a quick growing crop which requires good aeration in the soil. It is very susceptible to poor aeration and water logging conditions. Intercultural with khurpi or hoe helps in removing the weeds and improves aeration in the soil.
Water management
Water requirement of tobacco crop depends upon the type of tobacco and the region where it is grown. The irrigation requirement of tobacco crop often depends on the distribution of rainfall, soil moisture status, stage of crop growth. In order to raise a successful crop on light soils it is necessary that correct quality of water is given through timely irrigations. Too much irrigation leaches the nutrients from the soil and produces slick leaf with dirty colour. Insufficient irrigation, on the other hand, restricts crop growth and the curing of leaf becomes difficult.
Topping
It is most important operation for quality of tobacco leaf. It gives a uniform quality product and prevents excessive coarseness in the leaves. It prevents the plants from producing seeds and allows carbohydrates and nutrients to go towards vegetative part instead of reproductive. It causes thickening of the leaves and increase their body. It helps in the increment of sugar and nicotine content especially in the upper leaves.
Desuckering
Because of the topping the dormant buds in the axils of leaves becomes active and develop into shoots known as sucker. Removal of these suckers or lateral branches is called desuckering. Suckers should be removed as soon as they are large enough to be pulled.
Harvesting
In tobacco the leaves do not ripe uniformly. The first to ripe are the lower old leaves then the middle ones follow and after that upper leaves. The ripening process in the tobacco plants consists in the deposition of starch and gradual elimination of green coloring matters. So, when the leaves are ready to harvest they turn into lighter shade of green to slightly yellow colour and become thick and so brittle that when a section of leaf is folded between figures it snaps easily. Usually harvesting starts after 55-60 days of transplanting. Generally 2 methods of harvesting are practiced. They are
1) Priming
2) Stalk cutting
1) Priming: In this method, harvesting starts from the bottom and each time 2- 3 leaves are harvested at weekly interval. The entire harvesting is completed in about 5-6 priming. After harvesting the leaves are strung on bamboo sticks @ of 100 leaves per stick and are loaded in the barn for curing.
2) Stalk cutting: The entire plant is cut close to the ground with sharp sickle and left over night in the field for curing. The stalk is then hung upon a stick. It is done by piercing the stalk near its base with a removable metal placed on the end of the stick. A stick holds 6 to 8 stalks. Plants are allowed to wilt for 4-5 days. Wilted plants are easier to handle without damage. The leaves are not removed from the stalk until curing is finished.
PROCESSING
Curing
It is most important operation in tobacco production. It is done in order to impart the required colour, texture and aroma to the final product. Curing involves the process of drying decomposition of chlorophyll until the green colour disappears from the leaf.
Different types of curing
1) Flue curing: The harvested leaves are strung on bamboo sticks which are then placed on flue cured barn. Flue curing is usually done in brick barns. The green leaves are loaded on the upper half and lighter ones on lower half. Curing process consists of three main stages:
i) Yellowing of the leaf: For yellowing of the leaf, a temperature ranging from 26 to 28.3˚C is kept during the first 12 hours and then raised to 36.6 ˚C for the next 6-7 hours. After that temperature of 36.6 to 37.7 ˚C are used for 12-15 hours when the leaves become yellow. The main objective is to give optimum humidity and retain as moisture as possible to keep the leaves alive for 30-36 hrs.
ii) Fixing the colour: After yellowing the temperature is gradually raised and humidity is lowered by opening ventilation. Temperature is increased from 37.7 to 48.8˚C in order to kill the leaf, destroy the enzymes and dry out the web of the leaf. At this stage the leaves becomes dry but the midrib and the vein still contain some moisture. So fixing is a critical process and should be carried out with great care. About 80% of the moisture should be driven off. It takes about 12 to 24 hrs.
iii) Drying of the leaf: It lasts from 28 to 50hrs. The ventilators are closed and the temperature is raised up to 74˚C in order to dry the veins and midrib. After this process, ventilators are opened to cool down the barn. The leaves are left in barn overnight for absorbing moisture and to come to normal condition for handling and storage.
2. Air curing: This is a natural process and curing is done in a wooden barn under normal atmospheric conditions. The leaf should be yellow before it dries out and after that the rate of drying is gradually increased by increasing ventilation. After this, leaves are placed in a pit for 24 hours and then transferred to 2nd pit for 48 hours and then back to first pit for 24-48 hours. During this process, fermentation of leaves takes place and leaves attain dark brown colour with fruity smell.
3. Fire curing: Leaves are harvested in such a way that a small portion of stem remains attached to leaves. The leaves are allowed to wilt in the field for few hours, the tied into the bundles and then hung in a smoke hut. They are smoked for about 12 hours by burning dried leaves of trees. After this dried leaves are fermented in bulk for 3-4 weeks. The fermented leaves are then treated with salt water.
4. Sun curing: Most commonly adopted method by Nepalese farmers. There are several modifications in sun curing:
a) Curing whole plants on racks.
After initial wilting in the field the plants are strung on bamboo poles and cured in sun. The entire process takes about 15 to 20 days.
b) Curing leaves with pieces of stem on racks.
In this method of curing, racks are not exposed on the direct sun, therefore it takes longer period. (6-8 weeks).
c) Curing whole plant on the ground.
In this curing, leaves are allowed to dry in sun on the ground and are turned over twice a day. This process continues for about a week and then heaps are made which are opened on the next day and reheaped.
This process of heaping, opening of heaps, and spreading and reheaping continues for about 10 to 15 days.
By the end of this period leaves become completely cured.
REFERENCE:
Writer : Manoj Sapkota (College : Gauradaha Agriculture Campus, Jhapa)