Studies on Corresponded-Relations between Plant Characters and Cultivation Methods : III. Comparison of water balance in plants at transplanting among millets

摘要

Some experiments on transpiration and water absorption were conducted to determine the different rooting ability of millets at the time of transplanting from the viewpoint of water balance in the plant. This report also contains work on the effect of seedling quality on rooting. These experiments were done during the period from 1978 to 1981. The results obtained were as follows: 1. Transpiration rate per leaf arca was the highest in Japanese barnyard millet and the lowest in sorghum under the condition of water culture. Among the seedlings from the nursery bed filled with volcanic soil, however, Italian millet showed the highest transpiration, and the low values were seen in common millet and Japanese barnyard millet (Table 1). 2. The reason why Italian millet was subject to losing water balance in the plant at transplanting time, compared with finger millet were as follows: (1) Water content of the plant organs was lower in Italian millet and its transpiration rate was higher. This might be due to the higher stomata density per leaf area. (2) Top/Root ratio of Italian millet is extremely high and it becomes still higher by unavoidable cutting of roots at the time of transplanting. This results in a considerable decrease in water absorption by roots, although Italian millet has high water absorption rate and high level of bleeding water per root dry matter weight. This decrease in water absorption compared to a higher transpiration rate of leaves may result in losing water balance in Italian millet. On the other hand, finger millet had lower water absorption and also lower bleeding water level per root dry matter weight. But this crop had a high water content in its plant organs and a lower ratio of Top/Root. Therefore, the water balance can be kept in the plant. In the case of sorghum, ablility of water absorption and bleeding was low and the water balance in the plant may be kept with lower water contents because of its lower transpiration rate due to fewer stomata per leaf area. Japanese barnyard millet and common millet showed a similar tendency to finger millet and Italian millet, respectively (Table 2 and 3, Figs. 4-5). 3. To understand the effect of seedling quality on taking root, the rooting ability of seedlings grown at different fertilizer levels was investigated. New roots were more numerous in the seedlings of the standard fertilizer plot than the non-fertilizer application plot. The longest root was found in the seedling of the non-fertilizer plot. In the high fertilizer plot, only finger millet could produce more roots. Two weeks after transplanting, plants from the standard level plot showed greater growth, whereas common millet, Japanese barnyard millet and Italian millet displayed less growth at a higher level of fertilizer than the standard level (Table 4 and 5). From the above results, the higher Top/Root ratio is likely to cause taking root to fail at transplanting mainly due to damage of roots by pulling seedlings from the nursery bed, and the resultant decrease of water absorption by roots and loss of water balance in the plant can be seen. Therefore, especially the direct sowing type plants such as Italian millet and common millet are not suitable for transplanting. As to the effect of seeding quality on taking root, the seedings grown at the standard fertilizer levels generally showed good growth with many newly-emerged roots. But with a higher fertilizer level, all the millets except finger millet could not attain desirable growth.