Three varieties of lettuce, Tuk-sum, Ja-juk saik, and Great lakes 366 sowed on November 24, 1973 and Betted on January 8, 1974 were grown to study the effect of CO₂ concentration on plant growth. They were treated with 5 different concentrations of CO₂, 300 (control), 1000, 2000, 3000, 6000 ppm for 60 days from January 20 to March 20. Fresh and dry weight of shoots, leaf area and length and width of the largest leaf, total number of leaves, and weight of roots were measured at 20 days intervals after treatment. Total leaf area was also measured at the end of the treatment.
Liquid carbon dioxide, a by-product of fertilizer factory was used as CO₂ source and the concentrations in the polyethylene plastic growth chambers were determined by alkali absorption.
Tuk-sum and Ja-juk saik began to show visible effect in 10 days of treatment, it was particularly true when the 6000 ppm plot was compared with the control. Great lakes 366, which is head type, began to show visible effect on growth in 20 days and to form readily in 35 days of treatment. However, in the highest concentration the effect on shoot growth was negligible for the doubled concentration even though for root weight increased markedly.
The favorable effect of CO₂ treatment on the growth of headed type lettuce was expressed as the increased weight of head leaves with less outer leaves.
|