Temperature limitation

Since assimilation is an enzymatic process and thus temperature dependent (Downes, 1970), after the calculation of daily total gross CO2 assimilation rate (see topic Daily gross assimilation), WOFOST introduces a correction factor, function of air minimum temperature.

In fact, at night, assimilates produced during daytime are transformed into structural biomass. This process is hampered by low temperature. If these low temperatures prevail for a several days, assimilates accumulate in the plant and the assimilation rate diminishes and ultimately halts.

For accounting this process, firstly there is the calculation of the average minimum air temperature of the last seven days:

where AvTmin is air minimum average temperature of the last seven days (°C) and Tmin,i is air minimum temperature of the day i (°C).

Then, an AFGEN table is applied for deriving a nighttime temperature correction factor, function of air minimum average temperature of the last seven days (AvTmin).

Finally, the daily total gross CO2 assimilation rate is multiplied to this factor with the equation:

where Asstot,T is daily total gross CO2 assimilation rate with temperature limitation (kg ha-1 d-1), , Asstot is daily total gross CO2 assimilation rate (kg ha-1 d-1) and Cnight is nighttime temperature correction factor (unitless).

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