Effects of the application time of nitrogen on the rate of nitrogen absorption as related to top growth, and formation and thickening of tuberous roots in sweet potato

Abstract

Experiments on the application time of nitrogen fertilizer were carried out to clarify the mechanism of the formation and thickening of tuberous roots in sweet potato. Four types of soil classes, that is, sand, sandy loam, loam and clayey loam were used.In sandy soils, the application of nitrogen at about 30 days after planting was unfavorable to tuberous root formation during the one month period, mid-July to mid-August, because the higher rate of nitrogen absorption produced the vines growing vi gorously. However, the marked nitrogen absorption during the period of thickening growth after tube rous root initiation was favorable to the increase of yield of tuberous roots.In clayey soil, the application of nitrogen until 10 days after planting was favorable to both formation and thickening of tuberous roots due to the vigorous growth of vines having the high rates of nitrogen absorption throughout the growing season. Such a nitrogen status caused a higher yield of tuberous roots.