Two cultivars of soybean (Glycine max (L.) Merr. cvs. Essex and Williams 82) were grown from seeds in pots (7.5-L) filled with a mixture of sand and soil (1:2 by volume in 2004 and 3:5 by volume in 2007 and 2008) in the greenhouse at Purdue University, West Lafayette, IN (40.5°N, 87°W). The greenhouse was set to have day/night air temperatures of 26°C/20°C respectively; relative humidity (RH) of
70%, an 18 hour photoperiod with photosynthetic photon flux density (PPFD) measured during solar noon at the seedling top height of at least 180 ^mol m-2 s-1 when only the sodium lamps provided PPFD in the early morning and late afternoon during the winter.
Plants were watered with tap water three to four times a week in 2004 and 2007 and five times a week in 2008. No fertilizer was applied to the soil medium. In 2004, whiteflies infested the greenhouse. Plants were periodically sprayed with Conserve SC (Dow AgroSciences, Indianapolis, IN) to minimize herbivory.
Plants of the two cultivars (Essex and Williams 82 cv.) were planted in 2004 at the Purdue Agronomic Center for Research and Education at West Lafayette, IN (40.5°N, 87°W) with 15 in. spacing in 40 ft long rows, buffered on either side by eight rows of a commercial variety. The plants were allowed to emerge and develop for 14 days prior to the establishment of the filter treatments. Plants used in the experiment were grown near the center of each filtered radiation plot. The plants were watered solely from precipitation.
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