1970 Volume 39 Issue 2 Pages 107-114
1. In order to clarify the effects of drought and moist soil condition on the acid change of Satsuma orange fruits from mid-summer (after 3 months from blooming) until the harvest, pot experiment carried out with 4- and 5-years-old early Satsuma orange trees.
2. In experiment used much bearing trees, growth of fruits was greatly inhibited under drought soil condition during 20 or 30 days in August and September, and water content in flesh (flavedo) remarkably decreased. Soil drought resulted in higher acid concentration (g as free citric acid per 100ml. of juice), but in lower acid content in flesh (g as free citric acid per fruit) as compared to no drought. When irrigated water was sufficiently supplied during 5 days followed from the end of each drought periods, water content in flesh increased rapidly, and simultaneously acid concentration decreased remarkably, in while acid content of flesh increased. Aboved changes of acid due to soil drought and irrigation, were more conspicuous in the case of drought treatment from early August to early September than in that in middle or late September.
3. Acid concentration in middle August was already in decreasing process, and peak concentration appears to be at late July or early August, depending on the year. Decrease of acid concentration during the period from middle August to middle or late September which enlargement of fruits is most great, was rapid, and gradual after late September. On the other hand, peak content of acid in flesh was found during the period middle to late September. Therefore, change of acid was apparently differentiated into two process as follows; accumulation before middle or late September and decrease (or disappearance) after this time. Disappearance of acid after this time was actual decrease in total amount caused by a change in nutritional metaboliom of fruits. Great difference depending on the time of drought treatment on the decrease of acid concentration and increase of acid content which were occurred by the irrigation followed from the end of drought period, appeared to be associated with accumulation and decrease in process of acid change.
4. In experiment of soil moisture variation during 2 months of September and October usea less bearing trees, fruits grew larger in moist condition than in drought condition, and had lower acid concentration. Compared of acid change in fruits between moist and drought condition during about one month before the harvest, November 5, actual decrease was greater under drought condition. Fruits grown under drought condition had the qualities such as thin peel, deep coloring and high soluble solids concentration.
5. In conclusion, acid concentration of Satsuma orange fruits was affected greatly by the variation of soil moisture in late summer and autumn, especially after middle or late September. Poor fruit quality, watery taste, occurring frequently under rainy condition or excessive irrigation in late summer and autumn, appeared to be closely related with dilution caused by the increase of flesh water.