Abstract
In a previous paper, authors classified alfalfa varieties (Medicago sativa L.) into five groups according to their growth habits. Our present paper is a report of investigation on the growth habits of each group in its ecological aspect. In the experiment 59 varieties were used for materials. The comparative study of five groups on the multiple correlations among daylength, temperature and plant height throughout various growing periods between cutting dates in the natural environment for three years starting from 1965 was conducted. The results were as follows: 1. The simple correlation between plant height increase per day and daylength was 0.820 and the simple correation between plant height and temperature was 0.590. From this, it is confirmed that alfalfa is affected quite sensitively by daylength, and temperature is a secondary factor. 2. As to the simple correlations between daylength and plant height among the groups, 0.714 (lowest) was for group I and about 0.84 for the group IV and V. The correlations for the group V tended generally to exceed that for group I. Varieties of the group I originating from the low-latitude region were insensitive to daylength. On the other hand, varieties of the group IV and V originating from the high-latitude were very sensitive. 3. The resting period and the critical time for fall harvest were estimated through the photothermograph at the experiment station. As varieties of the group V had three months of dormant period, such group might not be utilized after about Oct.20 for fall harvest. In varieties for the group I, the dormant period was very short and the fall utilization might be possible up to about Nov.20. The utilization period of such group could be longer by one month than the group V. 4. The critical daylength for alfalfa dormancy in winter period was between 9.2 hours for the group I and 10.4 hours for the group V, judging from calculation through the regrssion on plant hegiht and daylength. The limit temperature to the fall dormancy was between 6.9℃ for the group I and 13.6℃ for the group V. From the above results, it is concluded that great emphasis should be placed on photoperiodic factor rather than temperature factor in alfalfa cultivation. Moreover, it is also concluded that varieties of the group I and II with high ecological adaptability to the warm region should be used for cultivation in the south-western warm region in Japan.
