Influence of Environmental Conditions in the Glass Room of the Phytotron on the Uniformity in Growth of Soybean Plants

Abstract

This experiment was performed in the phytotron of the Hokkaido National Agricultural Station to clarify the interrelationships between the distribution of air temperature or wind velocity and the characteristics of soybean plants grown in the natural light room.Seventy two pots, each of which has two plants standing in an east-west direction, were arranged on the twelve trolleys in unf ormity.Horizontal distribution of air temperature in the foliage zone of 70 cm height revealed that there was a thermal difference of 1.5°C between the wall side and the south side with a steady decline in temperature as the distance from the wall was farther. The wind velocity at a height of 70 cm ranged from 20 to 30 cm/sec at the most of measuring points, and it was found that there was negative correlation between wind velocity and stem elongation. Futhermore, it was shown that the distribution pattern of these two environmental factors under plant growing condition in 70 cm height was almost similar to those under an empty condition.The stem length and the fresh weight of soybean plants increased as the plants were grown farther from the wall. Within the pot-trolleys, the average stem length of the inner row is steadily higher than those of the outer. A similar tendency was also observed in the fresh weight measured 57 days after planting. The number of days to flowering from sowing was delayed at the south side as compared with those of the plants at the wall side.From these facts mentioned above, it is clear that increased stem length, fresh weight and delayed flowering time were due to low temperature and high wind velocity. Decreased stem length at the wall side resulted from the elevated temperature near the wall causing by the flux of sensible heat and by the reflection of light from the wall.The coefficient of variation of the stem length was 8.1 per cent and was smaller than that of field grown plants and was greater than that of the plants grown in the glass house having no equipment for thermal controlling, as shown in Table 2. It is desirable to use any adequate methods in order to reduce coefficent variation, in the case of more accurate experiments required in the glass rooms of the phytotron.