1966 Volume 35 Issue 1 Pages 8-18
To make clear the cause of alternate bearing of citrus trees from the nutritious point of view, the seasonal change of nitrogen, phosphoric acid and potassium absorption was observed in Kanagawa Prefecture with mature alternate and annual bearing Unshu orange trees on poncirus rootstocks.
1. The ratio of non-fruiting to fruiting shoots by number was 7:1 on the off-year tree, 2:1 on the on-year tree and 2.3:1 on the annual bearer. Number of fruits per tree was the least on the off-year tree, but the percentage of dropped fruits was nearly the same in either tree of the on- or off-year, showing 69.1-66.4%.
2. The growth of current shoots on length and fresh weight ceased at the end of June. The growth rate on fresh weight was the greatest in June on the off-year tree, and in May on both the on-year tree and the annual bearer. The growth of fruit on fresh weight was very active from August to October, its maximum rate being in August. The ratio of fruits to current shoots by fresh weight was 20:1 on the on-year tree, 15:1 on the annual bearer and 3:1 on the off-year tree. Therefore, the total growth of shoots and fruits of a tree based on fresh weight was greatly affected by a load of fruits, its maximum rate being between August and October. But, when observed on dry weight, its maximum rate was greatest in May on the off-year tree, and in later than July on both the on-year tree and the annual bearer.
4. The total amount of nitrogen contained in shoots and fruits of a tree was greatest in June and September, particularly in June on the off-year tree, and in August on the on-year tree. However, on the annual bearer it was greatest in May-August and October, the maximum value being in August. The total amount of phosphoric acid in shoots and fruits of a tree was greatest in May-June, August and October on the on-year tree. In either case, non-fruiting or fruiting, the amount of potassium contained in current shoots decreased in September and October, the decreasing rate having no connection with a fruit load.
The total amounts of nutrients contained in all of shoots and fruits on a tree of different bearing habit are as follows:
Fugures in parentheses indicate the amount contained only in fruits.
