Crop Ecology

• Although tobacco is a tropical crop, it can be grown in a wide range of environments.
• Generally, N. rustica requires cooler climate as compared to N. tabacum.

a. Temperature

• Important factor that determines not only the success of tobacco production, but also the distribution of various species of Nicotiana.
• It can be grown in any latitude or altitude if a mean temperature of 21-31oC prevails for a period of 120 days a year.
• However, availability of 100-120 frost free days with a mean temperature of 26.7oC is a pre-requisite.
• Successfully cultivated in regions with daily mean temperature of 18-20oC for five months.
• For germination, tobacco seeds require minimum of 21°C temperature. Temperatures between 27 to 32°C are desirable for rapid and uniform germination and also control of root-rot disease. At these temperatures, seeds must germinate within 3 days of sowing.
• For better quality smoking tobacco, the leaves must mature in temperature > 20oC.
• However, higher temperature (>35oC) accompanied by bright sunshine and non-irrigated condition can lead to leaf burning.
• Cardinal temperature for germination of tobacco

b. Moisture

• Moisture loving plant with transpiration coefficient of 500-600.
• Considerable amount of water required to maintain leaf turgidity and to overcome the transpiration loss of an enormous leaf area.
• However, water logged condition is sensitive as it obstruct the vigorous root growth due to depletion of O2 from the root zone.
• A good quality tobacco crop requires 1800 mm water per ha but as a rainfed crop, requires at least 50 cm of well-distributed rainfall in crop period.
• In such low rainfall areas, the tobacco leaves are high in Nitrogen, Nicotine, Calcium and Other extracts and Acids, but low in Potash and soluble carbohydrate, thus affecting the tobacco quality.
• Thus, tobacco requires 100-115 cm of annual precipitation for successful production.
• Critical periods are seedling formation, rooting and rapid stem growth.
• Continuous rain during growing season leads to disease and thin, light leaves.
• Rainfall is undesirable at the time of maturation of the crop as gums and resins from the leaves are washed away and moreover, aids spreading of Cercospora.
• Moderate drought during crop period produce thicker, darker leaves with more gums, don’t ferment well, with low fire holding capacity and inferior in taste and aroma.
• In addition, severe drought causes leaf margins to dry up permanently, reducing the yield.
• Moreover, when the drought is broken late in the season, new growth is stimulated in the inner portion of the lamina near the midrib resulting puckering causing rough appearance, delayed ripening and inferior quality.
• This shows that water deficit any stages of crop growth causes considerable losses in yield and quality of tobacco.

Rainfall requirement as per the stages of growth of tobacco

c. Light

• Light is a major climatic factor governing tobacco yield, the plant responding better to good sunshine during the growth period provided that there is no moisture deficiency as the yield is subjected to leaf growth in case of tobacco.
• Tobacco is generally neutral to day length in photoperiodic response, however, some strains like Maryland, Mammoth show short-day response.
• It is a known fact that day length and temperature compensate in their effect to some extent. Photoperiodic responses of many plants including tobacco may be modified by temperature.
• Tobacco that is to be used for cigar wrappers is frequently grown under artificial shade (using coarse burlap), reducing light intensity that favors the development of uniformly thin and uniformly colored leaves.
• Frequently, the plants are clipped to remove flowers, a process that promotes leaf size and quality.
• Higher light intensity during the growth period increases photosynthetic efficiency and better production.

d. Relative Humidity

• As tobacco is grown for its leaf, atmospheric humidity influences the quality and quantity of tobacco and curing of its leaves.
• Humidity that permits the harvested leaves to cure at the proper rate is important, yet the humidity should be sufficiently high at times during the year to make the leaves pliable enough to be handled without breakage.
• Relative humidity may vary from 70-80% in morning and 50-60% at mid-day.
• Drier weather is required for harvesting and ripening of tobacco.
• 85-90% RH is considered as optimum because at this level the leaves are easily used and they do not become very brittle.

e. Wind

• High wind speed at any stage of growth after seedling establishment is detrimental because the leaves splits and reduce the quality when the plants have enormous leaf area exposed to wind.
• However, tobacco is not suited to semi-arid regions not only because of high winds but also because of the low humidity, low summer rainfall and alkaline soils high in nitrogen.
• Tobacco is susceptible to air pollution as well. High concentration of ozone are known to cause a condition known as weather fleck- discolored margins and spots that lower leaf quality.

f. Soil requirements

• Generally, soils with good surface and internal drainage, adequate moisture retention and aeration preferred.
• The roots of tobacco are sensitive to aeration. In saturated soils, tobacco roots begin to die within 6-8 hr, with significant root loss occurring in as little as 12-24 hr..
• Soil requirements, however, vary with class of tobacco grown.
• light soil low soluble minerals due to low water holding capacity   larger leaves, light in color, fine texture, weak in aroma   so preferred for light colored flue-cured and oriental aromatic tobacco (humus <2%).
• Heavier soils (high silt and clay) smaller, dark, heavy leaves with strong aroma   so silty loam and silty clay loam preferred for burley and dark colored tobacco (humus 3-4%).
• pH: grown well on acid (4.5-4.8) to alkaline soils (8.5).
• Can be successfully grown even in heavy soils with more precautions to avoid soil compaction. These soils generally warm up and dry out more slowly in spring, so planting often delayed.