ワセウンシュウの隔年結果の防止に有効な最適葉果比

抄録

Using early ripening satsuma mandarin 'Miyagawa Wase' trees, yearly fluctuations in yields of each of three trees grown under four different conditions were examined for 20 years: 4-23 years old. The trees were planted at a density of 1, 250 trees/ha (2.8 m × 2.8 m) in volcanic ash soil. The cultural treatments adopted were (A) no pruning + no fruit thinning; (B) pruning + fruit thinning under no plowing + less fertilization condition; (C) no pruning + no fruit thinning and (D) pruning + fruit thinning under deep plowing + standard fertilization condition. The yields in no pruning + no fruit thinning plots (A and C) and in pruning + fruit thinning plots (B and D) increased while the trees were young although there were some yearly fluctuations. However, marked alternate bearing habits started at the 12th year in A and C plots, and at the 15th year in B and D plots. Using the data obtained from the year when alternate bearing started until the year the experiment finished when the trees were 23 years old, relationships between the number of fruits harvested per unit total leaf area on the tree in a given year and that in the following year were determined for each plot. The regression equation revealed that the number of leaves per fruit (leaf: fruit ratio) to attain the same yield the following year (no alternate bearing) was approximately 35 under the no plowing + less fertilization condition; the leaf :fruit ratio was 50 under the deep plowing + standard fertilization condition. Consequently it was concluded that to ameliorate or prevent the alternate bearing tendency of mature trees in plot B, the crop needs severe fruit thinning to reduce the leaf: fruit ratio to 35. Under plot D, the crop load needs to be decreased by fruit thinning to the leaf: fruit ratio 50. One solution to prevent alternate bearing would be to improve light interception by decreasing the tree density by tree removal. Further more, under plot B, fruit thinning to attain the leaf: fruit ratio of 35, the number of new leaves on spring shoots must be adjusted to the number of flower buds in the following year within a range essential for a high sustained yield.