抄録
The root system development of rice plants grown in the worked-and the sub-soils was investigated in a farmer's paddy field located in Akita Prefecture. After a soil monolith (10 × 10 cm with a depth of 40 cm, including a hill of rice plants) had been taken, the crown and lateral roots, which appeared in the 10 × 1O cm horizontal quadrate made at every 2.5 cm depth from 7.5 to 30.0 cm from the soil surface, were plotted. It was found that the numbers of crown and lateral roots appcaring in each horizontal quadrate gradually decreased from the depth of 7.5 cm downwards, and that the numbers of roots, especially those of lateral ones decreased markedly in the subsoil. In the compact subsoil demarcated from the worked-soil by a ploughsole (16 cm depth), both crown and lateral roots seemed to grow along the tube-shaped soil pore, and a case was found in which a crown root as well as lateral roots penetrated into other crown root in the same pore. These findings suggest the importance of soil structure in the compact subsoil for the growth of rice roots.
