Effects of heavy application of nitrogen and potassium on top growth, tuber-formation and -thickening of sweet potatoes grown on different types of soil

Abstract

Pot experiments were conducted to study the effects of heavy application of fertilizers on top growth, tuber-formation and -thickening of sweet potatoes. Four kinds of soil differing in their clay content were used. Amounts of nitrogen and potassium were applied each at three levels, the ratio of nitrogen to potassium being 1:1. One cutting was planted in each pot.Heavy application of fertilizers maintained the top growth vigorous throughout the growing period in every type of soil. The difference in top growth among the fertilizer levels was significant in the soils having higher clay contents.Though heavy application of fertilizers was unfavorable to tuber formation owing to the vigorous vine growth during the period of tuber formation, it increased tuber yield, especially that of large tubers, as it kept vine growth vigorous during tuber-thickening stage.The higher was the clay content of of soil, the higher was the fertilizer level favoring the highest dry matter content of tubers, with the exception of clay loam, containing the largest amount of clay among the soils used, in which it was rather low.