Journal of the Japanese Society for Horticultural Science
Online ISSN : 1880-358X
Print ISSN : 0013-7626
ISSN-L : 0013-7626
Investigations on the cause and control of alternate bearing of Satsuma orange (Citrus unshiu MAR.) trees. VIII
Effect of fruit thinning, pruning and fertilizer application
Chisho OGAKIKatsuji FUJITAHideo ITO
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JOURNAL FREE ACCESS

1968 Volume 37 Issue 4 Pages 312-318

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Abstract
1. The trees used for the experiments were Tujimura Unshiu orange of 18-year-old. The trees had been very vigorus and the difference between production in the“on”and“off”years had been quite pronounced.
2. Treatment
(1) Fruit-thinning
Fruits were thinned on July 18th and 19th. The number of fruit left on a tree at thinning was determined by the amount of leaf surface. Fruits were reduced so as to have 20 to 25 leaves to each fruit left.
(2) Fertilizer application
(a) Abundant amount application : Orchard was sod-mulched and nitrogen (18.6kg), phosphorus (16.8kg) and potassium (20.4kg) per 10 are were applied in three applications, at the beginning of spring, summer and fall.
(b) Small amount application : Orchard was non-mulched and nitrogen (13.5kg), phosphorus (11.25kg) and potassium (11.25kg) per 10 are were applied at the beginning of spring.
(3) Pruning
The trees were pruned in March. (Table 3)
(a) Moderate pruning: In the case of the on-year tree in the preceding season, shoots were thinned out moderately and the fruited shoots were cut back. In the case of the off-year tree in the preceding season, spring flush, summer and fall flushes were moderately thinned out.
(b) Heavy pruning : Shoots were rather heavily cut back.
3. Results
Heavy crop caused the depletion of food supply and reduced the storage of carbohydrates and other substances in the plant body. It reduced the growth of all parts of the tree and the formation of flower buds in the succeeding year.
The reduction of the crop had a favorable effect in maintaining annual bearing condition. Fruit thinning changed most effectively alternate bearing habit to annual bearing condition.
The trees which had shown strong alternate bearing tendency in the past several seasons required moderate pruning and abundant application of fertilizer in addition to the fruit thinning to recover.
The fertilizer application promoted the vegetative growth and also fruit growth.
Pruning with a moderate thinning stimulated the flowering shoot growth in the succeeding year.
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