抄録
A lot of experimental results indicates that an abundant application of potassium to the sweet potato leads to an increased tuber yield, though it is less effective to the growth of top. Potassium contained in the leaf of sweet potato is quite effective for maintaining photosynthetic activity, thereby contributing to increase the dry weight of the plant. However, it is unknown why potassium promotes the growth of tubers. Therefore, experiments were carried out by gravel culture or by field culture to acquire the information concerning the relationship between potassium and growth of tubers. The sweet potato plants cultured with various cultural solutions showed an intimate relationship between their tuber weight and K2O/N ratio in the tuber. A high K2O/N ratio in the tuber was combined both with a low ratio of water soluble nitrogen to total nitrogen content and with a low total nitrogen concentration in fresh tuber, this in turn, showing an intimate negative correlation with the net assimilation rate (Fig. 4). Also, to increase the potassium/nitrogen ratio in dosage of fertilizer gave a favorable influence upon both the increment of tuber weight and net assimilation rate. In the field experiments where much potassium applied, the effects of potassium were recognized in bigger tuber weight, higher, net assimilation rate and increased water content in tubers. Above mentioned results suggest that potassium participates in either the protein metabolism, or the hydration of tuber tissue or both, which are the most fundamental processes included in the growth of tuber in some way. It is, therefore, highly possible that the promotion of tuber growth by potassium may result in the promotion of photosynthetic activity through the accelerated translocation of photosynthates from leaves to tubers.
