Abstract
Through the analysis of relationship between the change of top-growth and the development of roots during one month from mid-July to mid-August, pot experiments were carried out to make clear the effects of application time of nitrogenous fertilizer on the tuber-formation of sweet potatoes. Two types of soil differing in their clay content, that is, sand and clayey loam were used.
1. The later the application of nitrogen on sandy soil, the greater was the vines elongation from mid-July to mid-August. On the contrary, the sooner the application of nitrogenous fertilizer on clay soil, the more vigorously top-growth during this period was kept.
2. According to the delay of nitrogen application, total number of roots at the stage of mid-July was already smaller on clay soil than on sandy soil, and also the respective number of roots classfied from their diameter was the same. However, no differences was observed among those treatments on sandy soil as to the total number of tuber roots and flat roots next to tuber root, whereas the number of tuber root decreased with the delay of nitrogen.
3. As the results mentioned above, top-growth on sandy soil was kept vigorous during the period from mid-July to mid-August with the delay of nitrogen. The same trend was true on clay soil, too. Therefore, it was comfirmed that regardless of soil it was unfavorable to tuber-formation with the delay of nitrogen, owing to the increase of the distribution of the photosynthesis nutrients for the enhanced vines elongation during this period.
