The influences of phosphorus on ear and kernel formation in corn was examined in sand culture and field trial. In the sand culture Hewitt's nutrient solution excluding phosphorus was used. Phosphorus levels in the solution were maintained at 0.13mM and 2.66mM of NaH₂PO₄·2H₂O. Corn plants were allowed to grow at the low or high phosphorus level through growing season divided into three periods such as vegetative, reproductive and ripening period (table 1). Plants grown at the low phosphorus level for more than two periods produced barren ears. Barren ears produced in the I₁II₁III₂ treatment receiving the low phosphorus for the periods before silking time were due to depressed vegetative growth limiting assimilates for kernel initiation. On these barren ear a reduction in number of kernels occurred. While barren ears in the I₂II₁III₁ treatment receiving the low phosphorus for the periods after young ear formation were due to impeding flow of assimilate to the kernels. On the barren ears an increase in number of undeveloped kernels occurred. Barren ears in I₁II₁III₁ treatment receiving the low phosphorus throughout the growing periods were due to both limiting and impeding assimilate for kernel initiation and development and resulted in a reduction number of kernels and an increase in numder of undeveloped kernels. In the field trial conducted on the volcanic ash soil (Kuriyagawa soil) indicating low phosphorus availability, 1.5kg and 4.5kg per a in P₂O₅ of fertilizer phosphate were basal-dressed in bands. The heavy phosphorus application resulted in increased yields and reduced number of barren ears. The increase of yields was due partially to the reduction in number of barren ear plants and partially to better kernel development.