Infrared Energy as a Factor in Controlled Environments

The proportion of visible to infrared radiation varies in different growth chambers. Whether this might affect leaf temperature and plant growth was investigated in chambers with equal visible radiation. In one chamber infrared energy was half the total, while in two chambers it was 75% of the total. Photoperiods were 14 hours and day and night temperatures 25° and 20°C, respectively. Warm weather species tested were Zea mays, Phaseolus vulgaris, Gossypium hirsutum, Glycine max, and Sorghum vulgare. High infrared did not increase the leaf temperatures of Sorghum vulgare, but growth was better than under low infrared. In the other 4 species, slightly higher leaf temperatures were observed, but growth was not significantly increased by high infrared. Of the cool weather species, Pisum sativum L. (Alaska and Wando) and Vicia faba L., grew less; Avena saliva L. grew equally; and Brassica oleracea L. var. capitata grew better in high infrared. Leaf temperatures of these cool weather species were generally below ambient and were not appreciably affected by the proportion of infrared. The CO₂ was uncontrolled in one high infrared chamber and was 400 μl CO₂ liter or more. Except for G. max and P. vulgaris, the growth of the warm weather species was not significantly affected; however, all cool weather species grew best in this chamber. A sparing effect from infrared damage is induced by high CO₂.