The author studied the solar radiation in Okinawa in an attempt to find whether the irradiation in Okinawa is sufficient for pineapple culture. Results obtained are as follows:
The geographical distribution in the vicinity of Okinawa of global solar radiation estimated from the mean of possible sunshine percentage is shown in Fig. 1. Although Okinawa's annual global radiation is estimated at 130.5k ly/year, one of the largest amounts in Japan, the radiation in spring and winter is as small as in Kyusyu, despite Okinawa is in lower latitudes.
The global radiation calculated from cloud amount data indicates that Okinawa ranks among the small radiation areas of major pineapple growing areas in the world (Table 2).
Based on the light saturation point of 30klux to 50klux for the Smooth Cayenne variety obtained by Nose and others from 24 hourly carbon dioxide exchange experiments with intact plants 5 to 8 months old after planting, an attempt was done to evaluate photosynthetically useful solar radiation available to the variety in pineapple growing areas. Relationship between whole global radiation
R (k ly/month) and the global radiation
RP (k ly/month) integrated up to the radiation intensity equivalent to the illumination of a light saturation point has been obtained from radiation data for Naha, Okinawa,
R
P=a log
10R/b,
where,
a and
b are empirical constants depending on light saturation point.
Assuming that the above formula is applicable for other pineapple growing areas in Taiwan and Hawaii and that
RP is regarded as photosynthetically useful radiation, the radiation available to the Smooth Cayenne variety in Okinawa and the two areas has been calculated as shown in Table 4, using the estimated global solar radiation in Table 1. The result shows that the radiation in Okinawa in spring and winter is considerably smaller than that in the two areas.
It may be concluded from these studies that solar radiation in Okinawa, where the Smooth Cayenne variety is grown most, is not necessarily sufficient for the culture of this variety.
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