CO₂ ENRICHMENT AND LIGHT-DEPENDENT TEMPERATURE CONTROL IN GLASSHOUSE TOMATO PRODUCTION

Altogether, five different light-dependent regimes and three steady regimes were used in early heated tomato crops (sown 15 November); one of the steady regimes being repeated in each experiment as the control treatment.

The effects on total monetary returns of light-dependent regimes applied in the pre-planting stage were small and generally without significance. When applied in the post-planting stage (to the end of April) the results varied according to the nature of the light-dependent programme and to the prevailing light conditions. One light-dependent regime gave an impressive result in the first experiment when light conditions were generally above average but a less impressive result in the third experiment when light conditions were, on occasions, below average.

Delaying the onset of ventilation until a higher temperature was reached was beneficial irrespective of the type of temperature control used. It seems likely that this was due to both higher temperatures which increased early yields and to the consequent extension of the CO₂ enrichment periods which probably increased total yields.

In general, the results show that yields and monetary returns were enhanced with increasing temperature whether achieved with light-dependent or steady control.

There was no strong evidence to suggest that short-term temperature variations with light which occurred through the operation of the light-dependent control system affected the yields or monetary values of the crops.

Two further experiments have been carried out involving light-dependent control of night temperature. Temperature treatments were applied in which night temperatures were adjusted according to the level of solar radiation recorded during the previous day period. These were described as "variable", and in the control treatments described as "constant" consisted of unchanging night temperatures of 18°C and 16°C. No significant differences in yields or monetary returns resulted from the application of "variable" treatments in the pre-planting stage, and in the post-planting stage early yields and