Irradiance Distribution and Carbon-dioxide Flux in Forage Grass Canopies

Abstract

A description of the distribution of irradiation within a canopy has been developed from horizontal irradiance distribution data. Particular emphasis has been put on the treatment of diffuse light and the way in which this distribution is influenced by canopy structure. The treatment of diffuse light is based on a description of the total amount of sky subtended at some point in the canopy through gaps in the foliage. The amount of sky subtended is expressed in terms of a basic unit of solid angle and a range of light path ways through the foliage from the most likely to the least likely pathway. The results emphasize the importance of considering diffuse and direct light separately. Diffuse light is more uniformly distributed through the canopy profile and calculations show that diffuse light is utilized more efficiently for CO₂ uptake in the canopy than direct light, except near the top of the canopy. Further more it has been shown that erect canopies have a greater influx of CO₂ than prostrate canopies at all irradiance levels.