1963 Volume 32 Issue 4 Pages 319-325
In order to make clear the characteristics of transpiration of head forming vegetables such as lettuce, cabbage and chinese cabbage, their transpiration amount was measured by the transpiration chamber method in Taketoyo fields, Aichi prefecture in 1962. This paper deals mainly with the transpiration of lettuce. Varieties used were Great Lakes 659 (head lettuce) and Kakichisha (asparagus lettuce). The results obtained are as follows.
1. Transpiration amout and water requirement of head lettuce were less than those of asparagus lettuce. This tendency was found as well in the other heading vegetables as shown in Table 2. This is due to the fact that either amount of transpiration per unit dry matter weight or per unit leaf area of head lettuce was less than that of asparagus lettuce as shown in Tables 2 and 4.
2. Moisture content of heading lettuce was normally 2-3% higher than that of asparagus lettuce, owing to the higher moisture content of its heading parts as shown in Table 1. So it may be said that heading vegetables require less water than non-he ading ones.
2. The maximum transpiration amount per plant per day (from 6 a. m. to 6 p. m.); 322g in head lettuce and 462g in asparagus lettuce, appeared on May 30 when it was fine all day. The maximum relative transpiration rate appeared on July 8, when the lettuce was in the midst of heading or 15 days after the start of heading, as shown in Table 4. These facts suggest us that the transpiration amount per plant will be highest on a fine day when the lettuce is in the midst of heading.
3. Transpiration amount increased usually with the growth of plant, until the heading stage of head lettuce as shown in Table 4 and Fig. 3. Decrease of the transpiration after head formation might be due to the low transpiring power of old outer-leaves and of heading part in head lettuce. Young leaves transpired more water than old ones as shown in Table 3, when the transpiration was measured by the chamber method as shown in Fig. 2.
4. Among many characters of a plant, leaf area highly correlated with transpiration amount per plant in usual. Particularly, in the case of head lettuce, area of outer old leaves had the highest correlation with transpiration per plant as in Table 5.
5. Among meteorological factors, solar radiation had the highest correlation with transpiration amount as shown in Table 6.