SOME EFFECTS OF CO₂, AIR TEMPERATURE AND SUPPLEMENTARY ARTIFICIAL LIGHT ON THE GROWTH OF YOUNG TOMATO PLANTS

During the last three winter seasons, experiments have been carried out with young tomato plants grown at two levels of atmospheric CO₂ (normal and 1000 v.p.m.), two air temperature régimes (national "blue print" temperature and 2.2°C above "blueprint") and two levels of light (natural daylight and daylight supplemented with artificial light), in factorial combination. Supplementary light was the most effective single factor for improving the rate of plant growth, the time to first flower and the early crop.

Significant interactions between air temperature and CO₂ level were obtained which were not consistent from one season to another, and in the second year there was a second-order interaction between all three factors. Generally, however, the effects of higher CO₂ levels were not large enough to be statiscally significant and the effects of increased temperature levels were even smaller.

The results confirm earlier recommendations that supplementary light is an effective way of reducing the propagating time of young tomato seedlings, and is more effective than CO₂ enrichment.

Although in most cases the effects of CO₂ and artificial light were cumulative, the evidence is not strong enough to recommend the use of CO₂ as well as supplementary light in commercial practice. The use of higher temperature levels likewise cannot be recommended.