ISHS Acta Horticulturae 51: Symposium on Protected Cultivation of Flowers and Vegetables
THE RESPONSE OF THE HEATED GLASSHOUSE LETTUCE CROP TO IN SITU SUPPLEMENTS OF LOW ILLUMINANCE FLUORESCENT LIGHT |
| Authors: | D.J. Dennis, W.M. Dullforce |
| Abstract:
Fluorescent tubes mounted horizontally above the crop provided a light supplement of approximately 1 K lux for winter forcing lettuce of the "Southdown 5B" type during the short days and low solar radiation conditions of the North European winter. Comparisons were made between applications begun at different times of the day and night but given for the same period of time. The supplements were provided for the greater part of the growth period of the crop. The response was measured in terms of changes in dry matter, leaf area, stem length and time to head formation. The standard growth analysis characteristics were derived. The plants responded to the supplements at this low illuminance and statistically significant increases in relative growth rate for dry weight and leaf area and net assimilation rate were found for the period immediately after planting. When given at night these supplements also caused pronounced stem elongation but marketable heads frequently developed before bolting occurred. The supplemented plants produced heads about one week before non-illuminated plants. The practical implications of these results are discussed. | |
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