Abstract
Job’s-tears (Coix lacryma-jobi L. var frumentacea Makino), cv. Hatochikara was sown in an upland field converted from a paddy field at the densities of 2.8, 5.6, 6.3, 8.3, 11.1, 16.0 and 25.0 hill per m2. The dry weights of the stems and leaves and grain yield increased as the planting density increased up to 11.1 hill per m2. As the planting density increased further the dry weights of stems and leaves gradually increased but that of the grains decreased, and thus their sum remained at the same level. The dry weights of stems and leaves highly correlated with the number of stems (r=0.884**) and total number stem nodes (r=0.829**). The number of stems per plant was decreased by dense planting due to the reduced stem emergence and decreased survival rate of the stems. The number of bracts increased as the planting density increased up to 11.1 hill per m2, but slightly decreased at the higher density. The higher the planting density, the smaller the stem diameter, the lower the number of bracts. These results suggested that the number of bracts was reduced by dense planting through the reduced growth of stems. The number of kernels and grain yield highly correlated with the number of bracts, though the sterile kernels slightly increased as the planting density increased. From these results it was suggested that the decrease in grain yield caused by dense planting would be attributable mainly to the suppression of the emergence and growth of stems.
