THE INFLUENCE OF LIGHT, TEMPERATURE, CO2 CONCENTRATION AND COMPOST ON THE DEVELOPMENT OF TOMATO PLANTS IN GROWING-ROOMS
Four growing-rooms were used each containing two units of three-tiered benchwork. Lighting was provided by means of 5' 80 W white fluorescent tubes (Philips TL 33). A 12-hour photoperiod was standard and the period of treatment was 19 to 21 days.
The installed light capacity ranged from 160 to 240 w/yd2 (91.4 cm2) with the latter giving the best results. Low mounting heights (tubes 4" (10 cm) above plant level) were superior to higher mounting heights (11–12"/28–30.5 cm). A 16-hour photoperiod increased dry weight by 40.7% compared with a 12-hour photoperiod. Comparison of an 8-hour and 16-hour photoperiod combined with two light intensities (600 and 1,200 lm/ft2) indicated the tomato behaved as a short-day plant in relation to leaf production and inflorescence initiation.
A series of temperature régimes ranging from 66/62°F (18.9/16.7°C) to 85/85°F (29.4/29.4°C) were investigated. Growth rate increased with temperature up to 80/80°F (26.7/26.7°C). Constant temperatures were superior to differential temperature régimes with the same mean temperature.
Plants responded to CO2 enrichment up to 2,500 ppm, the highest level used in this series of trials. Where low levels of CO2 were used in combination with high temperatures (>80°F=26.7°C), plants developed a browning and constriction of the stem just beneath the cotyledons.
Standard UCEE compost (75% peat, 25% sand) was used for most experiments, but later trials showed that an all-peat compost gave superior results.
The saving in propagation time was up to 43 days and 24 days compared with unlighted and supplementary-lighted plants respectively. The period from sowing to 50% flowers open stage on the first truss was reduced to 53 days.
Flower bud numbers on the first inflorescence increased with temperatures up to 80/80°F (26.7/26.7°C), contrary to the widely-held belief that high temperatures decrease flower bud numbers.
Plant height and leaf numbers to the first truss increased with temperature and the lower the light intensity the greater the increase.