Working with fused phosphate, we have known that there are some areas in Shizuoka prefecture in which magnesium deficiency appears and crops rospond to magnesium dressing. In these areas, crop plants develop the visual hunger signs, resulting in restricted growth and reduced yield. The manurial effect of magnesium added in the from of magnesium salt or fused phosphate is remarkably excellent in these areas or soils. And so, practising the pot culture tests with magnesium-deficient soil taken from the foot of Mt. Fuji, we have ascertained that this element was very effective for increasing the grain yield acting as a carrier of phosphate in barley plants. At the time of harvest, most of the magnesium absorbed by barley plants was found in the ears, and the amount of phosphate accumulated in the ears of this plants was increased by the application of magnesium.