Studies on the Growth of Tobacco Roots : XII. Depth and velocity of culture solution in relation to roots activity

Abstract

For the purpose of finding the effect of culture condition on the activity of roots and the growth of aerial parts, tobacco plants of MC variety were water cultured using a specially devised hydroponic bed and tank. Dry matter production, amount of absorbed elements, respiratory rate and activity of roots were investigated with reference to the depth and velocity of the stream. The results obtained were as follows: 1. Dry matter production and physiological functions of roots such as the respiratory rate and activity were highest when the tobacco plants were grown on the solution 4 cm in depth. 2. When the speed of the culture solution was within 10.7 cm a minute, dry matter production and respiratory rate and activity of roots decreased proportionally with the decrease of stream velocity. Tobacco plants grown under low stream velocity showed lower absorption of elements than those grown on the high stream velocity. 3. In case of the velocity more than 10 cm a minute, dry weight was not proportional to the increase of stream velocity. Respiratory rate and activity of roots grown under high stream velocity was higher than that grown under low stream velocity. Amount of absorbed element was about the same level over the velocities more than 5 cm a minute. 4. There seemed to exist positive correlations between stream velocity and respiratory activity. The auther concludes from the experiment described above that the optimum depth of the solution is 4 cm and the optimum stream velocity is 10 cm a minute when the hydroponic bed 8 cm in height is used.