Articles
EFFECTS OF SEASON AND ARTIFICIAL LIGHT ON THE GROWTH AND DEVELOPMENT OF YOUNG TOMATO PLANTS
In the first place, changes in the growth resulting from the season between September and December were studied.
Compared with the leaf initiation, there was a steady increase in the time the plants took to reach a fresh weight of 10 g.
The leaf size was reduced gradually.
Compared with leaf initiation, it also took slightly longer before the first truss was initiated.
The reason for this was the slightly larger number of leaves formed below the first truss.
Next, the mid-winter growth of the plants was determined in relation to the differences in light which were of the same magnitude as during the season, but which were brought about by supplementary lighting.
The growth adjustments took place in about the same way as during the season.
In both cases, the differences were less at rather high temperatures than where temperatures had been reduced by 5°C. A row of 400 Watt H.P.I.-lamps, spaced at 80 cm intervals, had an effect on the growth of tomato plants up to a distance of about 7.5 m.
Measured in mid-winter, the changes in the growing period as a result of artificial lighting for 16.5 hours per day amounted to about 10% over the range of 10 to 1 W.m-2. This means that the difference in the growing period was about 1% per 1 W.m-2. It would therefore be difficult to measure the effects of small differences in radiation under glasshouse conditions.