The Effects of air Temperature on Growth of Young Tomato Plants in Natural Light Conditions

Abstract

With the aim of obtaining information about light and temperature relationships during the early weeks of growth of young tomato plants, measurements of the weekly dry weight increments were made with plants up to six weeks old. Growth took place in natural light conditions during a number of winter periods (October to March). The daily light-time integrals (foot candle hours) were recorded throughout the investigation. In three experiments, each extending over a whole winter period, plants were grown at one-day temperature, but at three levels of night temperature, namely (a) 4° F. lower than the day, (6) equal with the day, and (c) 4° F. higher than the day. The day temperature was 6o° F. (15 ∙ 5° C.), 64° F. (68°C.) and 68°F. (20°C.) respectively for the three experiments. The results are summarized as follows :1. With each day temperature, growth rates were lowest when night temperature was lower than the day.2. Comparison of the effects of the constant temperature regimes with the high night temperature regimes showed that with the day temperature at 60° F. the growth rate was generally higher when the night temperature was high. With higher day temperatures, however, this was not the case.3. There was little evidence that over this temperature range the temperature inducing maximum growth was related either to the light conditions or to the age of the plant.4. The response to night temperature was small by comparison with response to that of the day.5. The results suggest that in winter highest growth rates will be achieved if the night temperature is not lower than 64° F. and the day not lower than 68° F.The results of an experiment designed to evaluate the separate effects of day and night temperatures showed that, over the temperature range 6o° F. to 68° F., dry weight increased with the night temperature. However, a much larger increase resulted with a comparable temperature rise during the day. Stem length was unaffected by the level of the night temperature but increased markedly with the day temperature.The periods from pricking-out to both initiation and anthesis of the first two inflorescences were recorded for plants growing at 6o° F., 64° F. and 68° F. The temperature effect on the period to initiation was small. The inverse relationship between temperature and the period to anthesis was especially marked in low light conditions.The value of adjusting both the day and night temperatures in accordance with the day-to-day fluctuations of the natural light was assessed by comparison with other temperature regimes having the same mean over each 24 hours. In general, flowering and fruiting was earliest when the day and night temperatures were equal. No evidence was found to justify the technique of adjusting the temperature in accordance with the natural light.