1. With a view to elucidating the effects of potassium fertilization rates and of the three major elements of fertilizer on the growth, yield, and sweet glycoside (stevioside and rebaudioside A) percentage of kaa he-e (
Stevia rebaudiana Bertoni), the present studies were carried out by field (Latin square method) and pot (one-way classification) experiments both using plants in the first year growth, in 1978.
2. The respective 4 and 9 levels of the field and pot experiments were as follows, in parentheses the amount of fertilizer (unit : g) per plot of 5 m
2 and pot of 1/5000 a, being in order of N, P
2O
5, and K
2O:
K0 (25, 25, 0),
K1 (25, 25, 22. 5),
K2 (25, 25, 45),
K4 (25, 25, 90) ;
F0 (0, 0, 0),
F1 (0. 1, 0. 1, 0),
F2 (0. 1, 0. 1, 0. 045),
F3 (0. 1, 0. 1, 0.09),
F4 (0. 1, 0. 1, 0.18),
F5 (0. 1, 0. 1, 0.36),
F6 (0. 1, 0. 1, 0.72),
F7 (0, 0. 1, 0.09),
F8 (0. 1, 0, 0.09) .
3. Potassium had the smallest effect. Even when potassium was lacking, the plant height, node number, stem thickness, branch number, and root number were not significantly different from those of the control. The decrease in yield due to the lack of potassium was recognized only in the cases of raw leaves and raw stems in the field experiment.
4. The yields of tops, leaves, stems, and roots had a trend towards increase with increasing potassium fertilization rates, whereas those of floral parts had a trend towards decrease.
5. Phosphorus had the greatest effect second to nitrogen.
6. Flowering percentage had a trend towards decrease with increasing potassium fertilization rates.
7. Air dry percentage of tops, leaves, stems, floral parts, and roots had a trend towards increase with decreasing potassium fertilization rates.
8. The rates of leaf and stem yields to the tops had a trend towards increase with increasing potassium fertilization rates, whereas that of floral parts had a trend towards decrease.
9. The rates of tops, leaf, stem, and floral parts yields to the roots were irrespective of the potassium fertilization rates and irrespective of the presence or absence of any one of the three major elements.
10. Quantative analysis of sweet glycosides, stevioside and rebaudioside A, was made by a new method,
i. e. inner standard method using steviolbioside as standard.
11. The percentages of stevioside, rebaudioside A, and total of the former two, were irrespective of potassium fertilization rates and irrespective of the presence or absence of any one of the three major elements.
12. There was no correlation between the percentages of stevioside and rebaudioside A.
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