I. Effects of nitrogen supplying level and culture condition on the top growth and tubers formation of Ipomoea Batatas.
1) The low level nitrogen (A plot) 3 Milliequivalent per liter of nutrient solution stimulated tuber formation while the high level nitrogen B₁ and B₂ plot) of 10 milliequivalent par liter failed to form tuber though fibrous roots were seen much activated.
The suppressive offset of nitrogen on tuber formation in presumed to result from the direct suppressive effect of nitrogen or a certain biocatalystic effect rather than from any indirect effect though the stimulation to growth of tops of the competition with carbohydrates.
2) The addition of milligram area to murient solution stimulated the growth and increased fresh weight and dry weight of the aerid part while suppressed, a little, plant length.
3) The water culture method, which this experiment newly adopted, stimulated plant growth more than the gravel Culture method. And the treatment of low level nitrogen (A plot) in this water culture also saw a considerable degree of tuber formation, as in the case of gravel culture.
4) The foliar application of growth retardant B-nine suppressed the plant length only, with no other recognizable effect.
II. Effects of urea supplying level on the growth of IPOMOEA BATATAS.
1) The higher level of urea which was abserbed thy roots through nutrient solution suppressed top growth, such as plant length, number of leaves and fresh weight. And this can be attributed to the direct absorption of urea which was not ammonificated.
2) Although the higher level of nitrate nitrogen (B plot) made no tuber formation in previous experiment (Report-1), the higher level of urea nitrogen (A plot) made tuber formation possible in this experiment.
The ratio of tuber to top was, however, less in higher level of urea than in lower level of urea, and the suppressing effect was larger on tuber than on top
3) The foliar application of urea stimulated top growth while the higher level of urea absorbed by roots suppressed it, thought the amounts of urea supplied in two experiments were same.
Ratio of top to roots was larger in foliar application of urea (C plot) and less in root absorption of urea both of higher (B plot) and lower urea levels (A plot).
III. Effects of growth retardant etc. on the growth of IPMOEA BATATAS in relation to urea application.
1) B-nine (N-dinethyl amino-succinamic acid) is recognized as a growth retardant, suppressed the plat length irrespective of urea levels.
The treatment of gibberellin stimulated distinetly plant length, and the combined treatment of gibberellin length, and B-nine recovered completely the plant length which had been suppressed by B-nine.
2) B-nine increased fresh weight, especially, fresh weight of top both in lower and higher level of urea.
The degree of fresh weight increase varied according to concentrations of B-nine, of which the 0.15% of B-nine (B₁ plot) was the effective in higher level of urea. The effect of B-nine for increasing fresh weight was the largest in top next in tuber, and the least in fibrous roots. The ratio of fibrous roots to top was always decreased by B-nine application, which the ratio of tuber to top was contrary increased by B-nine in higher level of urea though decreased in lower level of urea.
3) Gibberellin treatment also increased fresh weight but the combined treatment (B₃+ GA plot) of gibberellin and B-nine was even more effective than any of single treatments.
Gibberellin and B-nine proved to be synergistic with fresh weight while reverse with plant length.
4) Considerable influences were abserved mainly in the length of plants and their fresh weight after B-nine treatment.
So that B-nine may be reguraded as a metabolic controller rather than as an antimetabolite.
5) The surpressed growth of plants cause by higher level of urea was normalized by B-nine treatment.
This fact suggested a further study on the applicability for practical use.
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