Abstract
The effects of soil density, fertility and moisture content on the growth and yield of sweet potato plant were observed under field condition on volcanic ash soil. The results indicated that the yields of top were increased under high density, much fertilization and high water content of soil, while the effects of these soil factors on the tuber formation was not entirely equal to that on top growth. Under good soil areation, wet or much fertilized conditions exerted favorable effects on the yield of tubers, on the other hand, under poor soil areation, the yield decreased even at the same moisture content or fertility level as the former. This pointed out that it was essential to keep the soil areation at high level, in order to increase the yield of tubers by applying water or much amount of fertilizer.
