Interaction of Light with a Plant Canopy*

The Kubelka–Munk (K–M) theory has been applied to light interaction with leaves stacked in a laboratory spectrophotometer. The theory can also be applied to an actual field plant canopy. The K–M theory is a two-parameter generalization of the one-parameter Bouguer–Lambert, or Beer’s law, relation. The older theory accounts for transmittance of a medium but not for reflectance. The K–M theory, however, yields a theoretical value both for reflectance and transmittance. The K–M theory is applied in this paper to the reflectance and transmittance of stacked mature cotton leaves over the spectral range 0.5–2.5 μ. The standard deviation between theory and experiment, after known biases are calculated and removed from the data, is about 1%—a discrepancy well within experimental error. A procedure is developed to apply the K–M theory to an actual plant canopy. The method involves regression analysis to light flux measurements within a plant canopy. Differential coefficients are derived for use in both stacked-leaf and canopy applications.