Rice and red rice interference.: I.: Response of red rice (Oryza sativa) to sowing rates of tropical japonica and indica rice cultivars

Field experiments were conducted at the Rice Research and Extension Center at Stuttgart, AR, in 1997 and 1998 to evaluate the growth response of Stuttgart strawhull (Stgstraw) red rice to sowing densities of 0, 50, 100, and 150 kg ha(-1) of 'Kaybonnet,' 'Guichao,' and 'PI 312777' rice cultivars. PI 312777 produced a greater leaf area index and tiller density than Kaybonnet when grown with red rice. In 1997, Stgstraw seed yields were lower when grown with PI 312777 and Guichao than with Kaybonnet. The increased weed population in 1998 did not increase seed yield production of red rice when grown with the three rice cultivars. The Stgstraw red rice seed yield was reduced when grown with 50 kg ha(-1) rice when compared with its yield in monoculture and was reduced further when grown with 100 and 150 kg ha(-1) rice. These results demonstrate that red rice was more competitive when compared with the tropical japonica Kaybonnet than the indica PI 312777. Despite its semidwarf stature, PI 312777 tended to suppress red rice more than did Guichao or Kaybonnet. The mechanisms responsible for this difference could be important keys to the effective use of weed-suppressive cultivars in reduced herbicide input systems.