Potential intercepted radiation

The fraction of incident solar radiation intercepted by the green canopy (f intG , unitless) is given by:

where Gx (MJ m -2 d -1 ) is the daily incident global solar radiation, PARx (MJ m -2 d -1 ) is the daily incident photosynthetically active solar radiation, ε (unitless) is the crop extinction coefficient of Gx, GLAI (m 2 m -2 ) is the accumulated green leaf area indexto the day before. The coefficient ε depends on the canopy structure and determines the ability of a canopy of a given leaf area index to intercept solar radiation. Its value is about 0.35-0.40 for canopies with vertical tendency, 0.40-0.50 with random (spherical) leaf angle distribution, 0.50-0.60 for heliotropic crops (sunflower).

The amount of daily incident PARx is approximated as a fraction fPARG (around 0.5) of daily incident Gx, thus daily intercepted PARx (IPARd, MJ m -2 d -1 ) is:

The amount of daily incident G x is estimated by setting f PARG = 1.

Such daily rates are accumulated to estimate crop biomass growth.

A total fraction of global solar radiation intercepted by the green canopy f intT (untiless), computed as follows, is used to correct crop development under conditions of water stress:

where the subscript ' indicates the day before.

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