Wheat
- The largest quantities of best wheat are produced in the areas favored with the cool and moist weather during a fairly long growing period followed by dry and warm weather to enable the grains to ripen properly.
- It is grown near the equator as well as 60oC N and 40oS latitudes
- Minimum, maximum and optimum (cardinal) temperatures for germination of wheat crops are 3-4.5oC, 30-32oC and 25oC respectively.
- A mean daily temperature of 15 to 20oC is optimum for growth and development. Higher temperatures of about 30 to 35oC have detrimental effects on growth. It can survive a temperature of -8 to -10oC in the spring during the early periods of its vegetative growth.
- Prevalence of warm temperature during the early growth wheat may retard heading. Temperature above 32oC prevailing 3 to 4 weeks after flowering may ripen the grain prematurely.
- High temperature coupled with high humidity may encourage the spread of rust causing reduction of yield. It requires approximately 100 frost free days during the growing period.
- Grain filling period is the most important period. High temperature and moisture stress during these periods reduces yield drastically.
- During heading and flowering stages excessively high or low temperature and drought are harmful to wheat. About 14-150C mean temperature is optimum for ripening stage.
- Temperature above 250C during ripening tends to depress grain weight due to energy loss through heavy transpiration.
- The crop is usually classified as long day crop requiring more than 12 hours day light. But the new wheat varieties have wide adoptability and a less photosensitive; rather they are more thermosensitive.
- In moisture stress condition, growth is abnormal; yield is reduced by the reduced number of seeds per plant and weight of the seeds per plant.