Effects of application of nitrogenous fertilizer and soil type on the top growth and tuber-formation and-thickening in sweetpotato

Abstract

Pot experiments were conducted on the effects of application of nitrogenous fertilizer and soil type on the top growth and tuber-formation and -thickening in sweetpotato. Four types of soil differing in their clay content were used.Application of whole amount of nitrogenous fertilizer at one time after cuttings were planted was unfavourable to tuber formation owing to the vigorous vine growth during the tuber formation. It was true to the thickening of tubers, too, because top growth was gradually weakened after tubers began to thicken.On the other hand, fractional application of nitrogenous fertilizer was favourable to both tuberformation and -thickening due to the limited growth of vines during tuber formation and also moderately maintained top growth during tuber thickening. Total weight of tubers was heavier in the fractionary application plot than in the basic application plot, though yield of large tubers was less in the former than in the latter.When nitrogen was almost doubled in its amount and was applied fractionally, yield of tubers was increased regardless of the amount of potassium on the sandy soil, while on the caly soil it wa sdecreased unless the amount of potassium was increased.