394 
ANNUAL RAINFALL (INCHES) 
Fig. 17. Hypothetical curves showing the relation- 
ship between cane yield and climate in Hawaii. 
dally when the annual rainfall is low. The Ko- 
hala results could be applied to other areas for 
estimating effective rainfall, as the rainfall 
characteristics are more or less similar through- 
out the islands. 
JUICE QUALITY 
The dry matter production of a sugar-cane 
crop can be related in a quantitative manner to 
the solar radiation and the amount of effective 
water applied, if cultural practices remain the 
same. The problem of juice quality is more 
complicated, however, and at present can be 
dealt with only in a rough empirical manner. 
The weather factors that favor high sucrose 
content are: 
PACIFIC SCIENCE, Vol. XVII, October 1963 
1 ) High radiation favors photosynthesis and 
formation of sucrose. 
2) Water supply should be adequate during 
the growing season, but should be followed by 
a dry period of about two months before har- 
vest. High rainfall during the ripening period 
will dilute the juice and cause a part of the 
sucrose to break down into other sugars. 
3) It is generally known that cool weather 
preceding the harvest season improves the su- 
crose content of the cane. Less well known, 
however, is the beneficial effect of large diurnal 
temperature range. Harrington (1923) and 
Morinaga (1926) have shown that alternating 
high and low temperatures hasten the germina- 
tion of seeds and bulbs. If the buds of sugar 
cane react as favorably towards a great range of 
temperature, then earlier suckering could be ex- 
pected, which would mean a greater number of 
mature stalks at harvest and hence a higher 
sucrose content. 
In summary, the ideal weather for high juice 
quality would be abundant sunshine, high tem- 
perature range, adequate water supply during 
the growing season, and dry and cool weather 
during the ripening period. A study of Figures 
7 and 8 would indicate that the Ewa, HC&S, 
Pioneer Mill, and Kekaha plantations have the 
best climate for good juice quality. 
It is true that we cannot modify the climate 
to such an extent as to appreciably improve the 
juice quality. Nevertheless, an understanding of 
0 10 2030 40 50 60 70 80 90 100 
WATER DEFICIT (INCHES) IN 2 YEARS 
Fig. 18. Relationships between annual rainfall and 
effective rainfall in Kohala, assuming varying soil- 
moisture storage capacities of 2, 3, and 4 inches. 
