Abstract: Using fluvo aquic sandy loam soil, adding metsulfuron into soil by diffusion, conserving water content of 35% and cultural temperature of 25℃±1℃, selecting sensitive Keng rice variety and measuring the rice length after six day′s culture could obtain better repeatation for metsulfuron soil bioassay. The residue of metsulfuron had harmful effect on rice seedling′s root growth for rendering rice root of the treatments shorter than that of the controls. The sensitivity of rice varieties to metsulfuron showed the following tendency: Conventional Keng rice (Japanica rice)>Glutionous rice and Hybrid Keng rice>Conventional Hsien rice (Indica rice)>Hybrid Hsien rice. The impact of soil metsulfuron residues on rice seedling′s length reached 0.01 significant level at 0.5μg/kg for almost all rice varieties being tested. 

Key words: metsulfuron, rice, sensitivity, bioassay