Abstract
Wooden frame experiments were carried out to clarify the suitable combination of nitrogenous dertilizer between the basic fertilizer and the side-fressing upon the tuber-formation and tuber-thickening growth in sweet potato. Four types of soil were used.
1. In spite of the differences of soil used, tuber yield at the plot of NH4NO3+(NH4)2SO4 was the highest among the following three treatments, that is, NH4NO3+(NH4)2SO4, NH4NO3+CO(NH2)2, and NH4•NO3+NH4NO3.
2. In the plot of NH4NO3+(NH4)2SO4, it was more unfavourable to tuber-formation than other treatments owing to the considerable elongation of vines during the tuber-formation stage from the middle of July to the middle of August. On the other hand, yield of tubers at the plot of NH4NO3+(NH4)2SO4 was increased, especially that of large tubers, as it was favourable to the accumulation of assimilation nutrients owing to the vigorous vine growth during the tuber-thickening period.
3. From the results of this investigation, it is evident that dry matter content of tubers at the plot of NH4NO3+(NH4)2SO4 was the highest among these treatments in the light soil, that is, sand to loam, with the exception of clayey loam, in which it was rather low.
