Effects of nitrogen sources on the top growth, tuber-fomation and its development of sweet potato

Abstract

With four kinds of soil, namely sand, sandy loam, loam and clayey loam, the effects of nitrogen sources on the top growth, tuber-formation and-thickening of sweet potatoes planted in wooden frame were investigated.
1) The plants supplied urea and nitrate ammonium obtained better result than sulfuric ammonium in tuber-formation and-thickening in all kinds of soil. It may be due to the following facts that the plants supplied urea and nitrate ammonium maintained the moderate top growth during the tuberformation period from mid-July to mid-August, and the enhanced top growth during the tuber thickening period.
2) Photosynthetic activity of the plants supplied sulfuric ammonium was comparatively high during the tuber thickening period, however, the yield of tuber, especially that of large tuber, was inferior to the plants supplied nitrate ammonium or urea, owing to the heavy repressed leaf area.
3) From the results of this experiment, it was also confirmed that both tuber-formation and-thickening are closely correlated with the process of top growth, as it was recognized in the previous works.