For each phase in the growth of cultivar, there is a temperature range within which growth and development is optimum. These temperature ranges are called cardinal temperature.
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i. Minimum – below which there is insufficient heat for biological activity.
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ii. Optimum – at which the rate of metabolic processes are at their maximum. 15-30°C
iii. Maximum – above which growth ceases. Cool season crops
Wheat, barley, potato, oats.
i. Grow best in cool weather period and grown in winter season (November to February)
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ii. Temperate crops
iii. Cardinal temperature
a. Maximum 30 – 38°C
b. Minimum 0 – 5°C
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c. Optimum 21 – 30°C
Warm season crops
Rice, sorghum, maize, sugarcane
i. Grown in monsoon season and summer season.
ii. Tropical crops.
iii. Cardinal temperature
a. Maximum 45 – 50°C
b. Minimum 15 – 20°C
c. Optimum 30 – 38°C