This model calculates the incidence of chalky grains as regression on temperature and solar radiation occurred during the whole ripening phase as shown in the following equation (Okada et al., 2009):

Where:

Q (%) is the percentage incidence of milky white grains on the dry mass of kernels;

δ (°C) represents the effective temperature daily accumulated over a fixed damage threshold temperature;

SR (MJ m-2) is the accumulated global solar radiation during the ripening period;

α, β, γ (unitless) are the coefficients of linear regression.

In particular the temperature factor (δ) is calculated as follow:

Where:

fi (unitless) is a daily factor modulating the grain susceptibility to chalkiness during the ripening progress.;

tb (°C) is the average temperature threshold beyond which the damage to grain begins to occurs;

ti (°C) is daily minimum air temperature occurring during the ripening period of rice.

Contrary to the model developed by Nagahata that assumes four fixed values of fi factor during the ripening progress, in this case fi is daily calculated using the following equation:

Where:

b (unitless) is a parameter regulating the duration of maximum grain.

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