Abstract
There is a intimate corelation between the absorption amount of potassium and tuber-yield of sweet potato in wide range. However, it had been vain attempted to increase the dosage of potassium application with ordinary procedure for get a very high yield. Then we carried out various experiments on the application method of potassium. In the investigation of root system of the sweet potato, a interesting fact was found out that the roots occurrenced from the stem were located in a shallow soil layer near of surface, but the roots developed from the tauber were located in deep soil layer. Another fact also recognized that abundantly potassium exist in deep soil layer at high-yield-field of sweet potato. Consequently, mineral nutrients were applicated the both layers, shallow and deep, through the plowing before planting. We got a conclusion as a follows; it is very effective in order to tuber-yield increasing to applicate the potassium in deep soil layer, 30 cm or 40 cm depth, at fertile soil, and it is desirable to applicate with together potassium, nitrogen and phosphorus at arid field.
