14.3.1 Day/night temperature differential

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Under normal field conditions mean day temperatures can commonly be 5°C to 10°C higher than mean night temperatures, with a much greater amplitude between maximum and minimum temperatures. The importance of this day/night differential (sometimes designated as thermoperiodicity) has received considerable attention in relation to the growth and yield of glasshouse crops where there is the possibility of some degree of temperature control. However, it is also of interest in field crops in relation to the development of models for use in predicting the effect of weather conditions on crop development.

Total plant growth would be favoured by low night temperatures as this would reduce respiratory losses at a time when the supply of carbohydrate might become limiting. However, dry matter production for a wide range of crops grown under constant but optimal temperature is equal to and often greater than dry matter production by the same crops grown under differential day/night temperatures with the same mean value. Where a day/night temperature differential is imposed, low night temperatures rather than low day temperatures favour growth. The amplitude of the day/night temperature differential is also important and increasing this from 10°C to 20°C can reduce growth.