Abstract
Effects of planting density on the formation of the root system and the relative growth of the top and root in rice plants were investigated. The four planting densities used were 45, 70, 95 and 120 hills per 3.3m2. The results obtained are follows: (1) The top-root ratio increased with increasing planting density, and thus the relative inferiority of root growth to top growth was amplified. (2) The root weights per unit area showed unimodal type time-course changes, which indicated the maximum weight immediately after the maximum tiller number stage, in the high density plots (95 and 120 hills), whereas in the low density plots (45 and 70 hills) they showed bimodal type time-course changes in which the root weights rose just after the maximum tiller number stage as well as at the heading stage. (3) The root system distributed in the surface soil layer became higher in ratios as the planting density increased. However, the roots in the surface soil layer in the high density plots decreased the weights strikingly in the later growth stages. (4) The total number of crown roots per unit area increased with increasing planting density, while the diameter of crown roots indicated a decreasing tendency.
