抄録
The mechanism of the excessive vegetative growth of sweet potatoes and the varietal differences were observed from the viewpoints of the soil physical conditions and the ecological charcteristics of roots. The results obtained may be summarized as follows. 1. If the aeration be suppressed owing to the compact soil, it would show a decrease in the weight of tuberous roots and an increase in T/R ratio, thus resulting in the excessive vegetative growth of sweet potatoes. In this case the varietal differences were observed. Norin No. 1 was subject to the excessive vegetative growth more readily than Okinawa No. 100. 2. It was proved that such varietal differences have bearing upon the differences in the distribution and the weight of non-tuberous roots. Namely, the non-tuberous roots of Norin No. 1, as compared with those of Okinawa No. 100, intruded more readily into such soil condition which caused the excessive vegetative growth, thus showing an increased rate of distribution of nonteberous roots in that place. In the case of the variety which is likely to subject to the excessive vegetative growth, it showed such characteristics that the weight of non-tuberous roots was great, and the ratio between the weight of tuberous roots and the weight of non-tuberous ones was low, and it was observed that those characteristics had high correlation with the ratio between the weight of tuberous roots and the total weight of dry matter, and it was proved also that those characteristics have an effect on the distribution of the dry matter. 3. On the other hand, varietal differences were observed also in the thickening of tuberous roots. It was proved that since Norin No. 1 was affected more greatly by the bulk density of soil than in the case of Okinawa No. 100, the thickening of tuberous roots of Norin No. 1 was more liable to have restrictions than the latter owing to the compact soil.
