Temperature

Air temperature is the main environmental component influencing vegetative growth, cluster development, fruit setting, fruit development, fruit ripening, and fruit quality The average 24-h temperature is believed to be responsible for the growth rate of the crop-the higher the average air temperature the faster the growth. It is also believed that the larger the variation in day-night air temperature, the taller the plant and the smaller the leaf size. Although maximum growth is known to occur at a day and night temperature of approximately 25°C, maximum fruit production is achieved with a night temperature of 18°C and a day temperature of 20° C. The recommended temperatures that follow are therefore a compromise and are designed for sustained, high fruit productivity combined with modest crop growth throughout the growing season.

Recommended air temperatures

Low light High light

With carbon dioxide

Night minimum 17°C 18°C

Ventilation 21°C 24°C

Note

  • When growing cold-tolerant, cultivars such as Vendor, air temperatures can be l-2°C lower than those indicated. However, when growing vigorous cultivars such as Ohio CR-6, the indicated temperatures are the absolute minimum.
  • During very bright weather, temperatures higher than 26°C do not harm the plants; but, above 29" C, blossoms of most cultivars sustain injury (Ohio CR-6 is an exception).
  • A minimum soil temperature of 14 °C is recommended.

Light is a prerequisite of plant growth. Plant matter is produced by the process of photosynthesis, which takes place only when light is absorbed by the chlorophyll (green pigment) in the green parts of the plant, mostly in the leaves. In the process of photosynthesis the energy of light is used in fixing atmospheric carbon dioxide with water in the plant to produce such carbohydrates as sugars and starch. Generally, the rate ofphotosynthesis is related to light intensity, but not proportionally. The importance of light in tomato production is greatest in the winter, when it is in short supply. In the short dull days of late fall, winter, and early spring, flower bud development is arrested and clusters fail to produce flowers and fruit. This failure is due to the low daily levels of radiant energy, which result in insufficient carbohydrate production. Not only do the poor light conditions limit photosynthetic productivity but the limited carbohydrates produced during the day are expended by the respiring plant so that it can survive through the long nights. A fully grown tomato crop benefits from any increase in natural light intensity, provided the plants are well supplied with water, nutrients, and carbon dioxide, and the air temperature is prevented from becoming too high.

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