Effects of temperature on acid and soluble solids in Satsuma oranges

Annual variations in the acid and soluble solids contents in Satsuma orange fruits were determined from the 8 year′s data in fertilizer and soil experiments which had been carried out over 10 years in Ehime Fruit Tree Experiment Station.The acid content of fruit juice varied with year of production, while the variation of soluble solids content was not so distinctive. In the fertilizer experiment, for example, acid content varied from 0.82 to 1.41g as citric acid per 100ml of juice, and soluble solids varied from 11.23 to 14.51g per 100ml of juice. Hence the acid largely affected on the ratio of solids to acid which varied from 10.0 to 13.7. Such tendency was similarly recognized in 3 different experiments.Summation of available heat above 13°C per month differed considerably from year to year. The diversity was most apparent in September, followed by June and July in order. To know the relations between monthly heat units and the acid or soluble solids content, correlation analysis has been made. Negative relation between the heat units and the acid contents was found in June, July and October, especially significant correlation in June. Similar trend was also shown in the results of experiment that air temperature was slightly raised by the covering of vinyl-cloth on the tree crown of Satsuma orange.Judging from the data obtained herein, acid contents appear to be affected by the temperature more than the fertilizer and soils. However, there was no significant correlation between available heat units and soluble solids or ratio of solids to acid.