Abstract
The experiments were carried out from 1967 to 1969 in Malaysia and in 1971 in Japan with the idential conditions and samples as the previous report. The solar radiation was calculated by the modified Budyko's formula. The results are summarized as follows:
1. In the individual plant, the total and daily transpiration increased particularly in the local long term varieties (Table 1) . This was a different trend to the plant population. Thus the transpiration was governed by the combined factors of plant growth and climatic conditions.
2. In the individual plant, the daily dry matter production of the new varieties was larger than that of local long term varieties, though that of IR 8 was not always large (Tables 1 and 2) . In the plant population, the total dry matter production was proportional to the length of growth duration until 140 days after transplanting (Fig. 1) . The panicle weight (yield) was the maximum at about 110 days of the growth duration, because panicle/straw ratio decreased in accordance with the advance of growth duration.
Although the total dry matter production of the new varieties was not large, the daily dry matter production of Bahagia was nearly equal to that of IR 8 and larger than that of Radio Ebos 33, and as to the daily grain production IR 8 was nearly the same as Bahagia and larger than R. Ebos 33 (Fig. 1 and table 3) . In short, though in the individual plant productivity IR 8 and Hoyoku, the varieties of good plant type, was not high as compared with the local varieties, the productivity of plant population of IR 8 was evidently high.
3. In the tropical plant population, according to the calculation based on water requirement, the efficiency of solar energy conversion was 1.4% (1.1-1.6%) for photosynthesis, on the presumption that about 40% of net assimilation was consumed by respiration, and was 0.9% (0.7-1.0%) for dry matter production (Table 3) . The efficiency was particularly lower in the local varieties as compared with that of the temperate rice.
The efficiency of solar energy utilization for evapo-transpiration was about 70% in average.
