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Measuring light interception in pots

Terry Bolger T.Bolger at pican.pi.csiro.au
Thu Sep 18 08:25:07 EST 1997

 I have a question regarding the appropriate protocol for measuring light
interception in plants growing in small pots (glasshouse experiment) and
treated as "mini-swards".  The pots are 15-cm in diameter, and contain
various densities of different grassland species (in monocultures).  To
reduce edge effects, we have put cylinders of white paper (borders) around
the outside of each pot, and raised it so the top of the paper is at
"average" sward height. 

Our initial thought was to use our line quantum sensor (custom made, 1cm x
1cm x 15 cm, GaAsP photocells) and simply take readings above the pots and
then at the bottom of the canopy (provision has been made for measurement at
ground level). However, we found that the light at ground level of a pot
without plants, fitted with a white cylinder to the average height of the
plants, was only about 50% of the light measured above the pot and cylinder.
Also the borders will be raised differentially over time as the species
grow.  So it appears to me that the appropriate "control" or reference
measurement for determining light interception is the light at ground level
of a pot with no plants and the border raised to the same height as on the
pot with plants for the corresponding measurement.  I would appreciate any
comments or input people would have about this situation or my intended

Terry Bolger
CSIRO Plant Industry
GPO Box 1600
Canberra, ACT  2601
email: terry.bolger at pi.csiro.au
phone: 61-2-6246-5445
fax:     61-2-6246-5399

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