Effects of plastic mulch color on upwardly reflected light and on the growth of tomato plants were investigated. Plants grown in sunlight over black polyethylene mulch had fewer axillary shoots (branches) and were taller than plants grown over white polyethylene mulch. The black surface reflected less total light and less blue light, but a higher ratio of far-red (FR) relative to red (R) light. In a controlled environment, tomato plants that were exposed to brief periods of FR at the end of the daily photosynthetic period were taller than those that received brief periods of R. The effect of FR on plant height could be reversed by R and implies phytochrome involvement. Differences in the light spectrum reflected from the plastic, and the similar differential responses to mulch color and light treatments, suggest that tomato plants grown in plastic mulch culture may respond to relatively small changes in light environment induced by the surface color of the mulch.
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