Abstract
Based on the experimental results obtained in previous paper XI, effects of air temperature and radiation on the seasonal dry matter production of orchardgrass sward were analysed in this paper. The results are as follows ; 1. The seasonal changes of air temperature and radiation in each region of Japan were affected by latitude and elevation. Generally, the seasonal changes of air temperature showed the mono peak curves which have a peak in August, but those of radiation varied with changes of latitude and elevation. The regions of higher latitude (Hokkaido districts) and higher elevation (central high land) had a peak of radiation in May or June, but those of lower latitude (south of Tohoku districts) had two peaks in April and August. 2. Calculated values of yearly dry matter production of orchardgrass sward in lower latitude regions were higher than those in higher latitude and higher elevation regions. On the other hand, yealy mean values of crop growth rate (<CGR>^^^) and productive efficiency of radiation (<PER>^^^) in lower latitude regions were lower than those in higher latitude and higher elevation regions. The high values of crop growth rate (<CGR>^^^) and productive efficiency of radiation (<PER>^^^) were obtained in the south-western section of Hokkaido districts, Tohoku districts and central high land. As the reason mentioned above, it may be considered that the most suitable air temperature (16℃) for production of orchardgrass sward was gained in the same season (May or June) of the highest radiation and air temperature in summer season was comparatively low in these regions. The yearly dry matter production, <CGR>^^^ and <PER>^^^ decreased in north-eastern section of Hokkaido districts, because the season (August) of the most suitable air temperature for production of orchardgrass sward did not agreed with the season (May) of the highest radiation and the air temperature during the growth season was comparatively low condition. The yearly dry matter production of south-western section (low latitude) in Japan increased owing to high radiation and long period of growth season, but <CGR>^^^ and <PER>^^^ decreased owing to high air temperatutre in summer season. 3. Changes of CGR of orchardgrass sward during the growth season showed the mono peak curves in the north-eastern section of Hokkaido (peak, August), in the southwestern section of Hokkaido (June) and in central high land (June). The changes of CGR in low latitude regions (south of Tohoku districts) showed two peaks curves which have peaks in spring and autumn season.
