GreenLab Course
Production-Expansion
Eco-physiology reminders
Thermal Time
Temperature controls both organogenesis (organ appearance) and organ growth.
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Thermal Time Tt is measured by calculating the daily accumulations of heat using temperature data.
Thermal time is expressed in Growing Degree Days (GDD).
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Tt = Σd=1,n ( Td - To )
where
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Td is the average daily temperature
To is the developmental threshold or base temperature under which the development rate is zero.
The base temperature varies with plant species: 8 o C for wheat, barley, soybean, up to 10 o C for maize, rice.
It is assumed that Td ≥ To, if not, Td is set to To.
Thermal Time and Development.
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It has been shown that biomass increases are proportional to thermal time.
Normalizing the development time with thermal time (instead of calendar time) allows development comparisons, as illustrated below on root elongations.
This example illustrates the Relative Elongation Rate (Graphs Granier and Tardieu, INRA)
- RER was measured according to calendar time (per day) compared to thermal time
(expressed in oC per day).