Light Transmission in Field Communities of Sorghum1
- Max D. Clegg,
- William W. Biggs,
- Jerry D. Eastin,
- Jerry W. Maranville and
- Charles Y. Sullivan2
Most plant canopy and solar radiation studies have comprised theoretical considerations, assuming a randomly oriented leaf arrangement. Lacking are field measurements concerning culturally arranged plant canopies in relation to interception of solar radiation. The purpose of this study was to describe the light environment under field conditions below and within grain sorghum (Sorghum bicolor (L.) Moench) canopies.
Visible radiation was measured in sorghum using sensors mounted on a traversing system and having about the same sensitivity to direction and spectrum as does a leaf. As much as 89% more light was transmitted to a sensor when it moved, between rows rather than across them. Therefore, measurement across rows is recommended.
Light transmission profiles of sorghum canopies on clear and cloudy days were similar. Differences between transmission values over a diurnal period were less on cloudy than on clear days indicating more uniform light distribution. Visible radiation transmitted through sorghum canopies of .51-m rows as compared to sorghum canopies of .76- and 1.02-m rows or sorghum, canopies of .76-m rows as compared to sorghum canopies of 1.02-m rows was less. This would indicate more visible radiation would be available for photosynthesis with narrower row spacings.
Extinction coefficients (K) for canopy layers were calculated and for each layer proceeding downward K decreased. Extinction coefficients of sorghum canopies of different row spacings decreased as row spacing increased. Differences between hourly values of K were less on the cloudy day than on the clear day. For all conditions minimum values of K occurred at solar noon. These results agree with theoretical data.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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