The daily insolation on a horizontal surface was 32 MJ $m^{−2}$ on a cloudless summer day.

a. Estimate the fraction τ of this daily energy receipt that would be measured at the bottom of a crop canopy with a leaf area index of 4.0.

b. Hence, estimate the fractional interception of solar radiation by the canopy.

c. Find the leaf area index that would intercept 95% of the daily radiation. (Assume a spherical leaf distribution for all parts of the question.)

Question

The daily insolation on a horizontal surface was 32 MJ [latex]m^{−2}[/latex] on a cloudless summer day.

a. Estimate the fraction τ of this daily energy receipt that would be measured at the bottom of a crop canopy with a leaf area index of 4.0.

b. Hence, estimate the fractional interception of solar radiation by the canopy.

c. Find the leaf area index that would intercept 95% of the daily radiation. (Assume a spherical leaf distribution for all parts of the question.)

Accepted Answer

Treat the radiation as diffuse when observed over a full day. Then Figure 8.3 gives [latex] \mathcal{K} = 0.67. [/latex]
i. [latex] τ = ext{ exp } (−0.67 × 3.0) = 0.13.[/latex]
ii. Interception [latex]= 1 − τ = 0.87.[/latex]
iii. [latex] (1 − 0.95) = ext{ exp } (−0.67 \ L); \ L = 4.5. [/latex]

Question 8.3: The daily insolation on a horizontal surface was 32 MJ m^−2 ...

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