Abstract
For the purpose of clearing up the suitable cultural conditions for the directly planted sweet potato plant, we compared the growth and yield between direct sowing and transplanting cultivation under several cultural conditions. The results were as follows; 1) Water content of soil; the smaller the water content of soil the larger the ratio of yield in top and root of directly sown plants to that of transplanted ones. 2) Kind of soil; we used 4 kinds of soils, that in black coloured volcanic ash soil rich in humus, brown coloured volcanic ash soil, alluvial clayey soil and sandy soil. The yield of roots of directly sown plants were larger than that of control in sandy soil and brown coloured volcanic ash soil, but on the contrary reversed in black coloured volcanic ash soil and aleuvial clayey soil. The former two soils contained much air porosity as compared with latter ones in wet conditions. At the directly sowing cultivation, air porosity of soil had a tendency to be on the decrease as cornpared with control at growing period, because it needed about 40 days before sprouting and soil loosened by ridging became compact at sprouting time. So such a soil which had a tendency to decrease the air porosity at wet conditions was not suitable for directly sowing cultivation. 3) Elevation of the field; the yield of roots of plant sown directly was larger than that of control on higher ground.
